Add 'run-as' command implementation as set-uid program.

Typical usage is 'run-as <package-name> <command>' to run <command>
in the data directory, and the user id, of <package-name> if, and only
if <package-name> is the name of an installed and debuggable application.

This relies on the /data/system/packages.list file generated by the
PackageManager service.

BEWARE: This is intended to be available on production devices !

5 files changed, 892 insertions, 0 deletions

diff --git a/run-as/Android.mk b/run-as/Android.mk
new file mode 100644
index 0000000..326f5af
--- /dev/null
+++ b/run-as/Android.mk
@@ -0,0 +1,12 @@
+LOCAL_PATH:= $(call my-dir)
+include $(CLEAR_VARS)
+
+LOCAL_SRC_FILES:= run-as.c package.c
+
+LOCAL_MODULE:= run-as
+
+LOCAL_FORCE_STATIC_EXECUTABLE := true
+
+LOCAL_STATIC_LIBRARIES := libc
+
+include $(BUILD_EXECUTABLE)
diff --git a/run-as/NOTICE b/run-as/NOTICE
new file mode 100644
index 0000000..c5b1efa
--- /dev/null
+++ b/run-as/NOTICE
@@ -0,0 +1,190 @@
+
+   Copyright (c) 2005-2008, The Android Open Source Project
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
+      source, and configuration files.
+
+      "Object" form shall mean any form resulting from mechanical
+      transformation or translation of a Source form, including but
+      not limited to compiled object code, generated documentation,
+      and conversions to other media types.
+
+      "Work" shall mean the work of authorship, whether in Source or
+      Object form, made available under the License, as indicated by a
+      copyright notice that is included in or attached to the work
+      (an example is provided in the Appendix below).
+
+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
+      the Work and Derivative Works thereof.
+
+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
+      or by an individual or Legal Entity authorized to submit on behalf of
+      the copyright owner. For the purposes of this definition, "submitted"
+      means any form of electronic, verbal, or written communication sent
+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
+      designated in writing by the copyright owner as "Not a Contribution."
+
+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
+      subsequently incorporated within the Work.
+
+   2. Grant of Copyright License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      copyright license to reproduce, prepare Derivative Works of,
+      publicly display, publicly perform, sublicense, and distribute the
+      Work and such Derivative Works in Source or Object form.
+
+   3. Grant of Patent License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      (except as stated in this section) patent license to make, have made,
+      use, offer to sell, sell, import, and otherwise transfer the Work,
+      where such license applies only to those patent claims licensable
+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
+      granted to You under this License for that Work shall terminate
+      as of the date such litigation is filed.
+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
+      (c) You must retain, in the Source form of any Derivative Works
+          that You distribute, all copyright, patent, trademark, and
+          attribution notices from the Source form of the Work,
+          excluding those notices that do not pertain to any part of
+          the Derivative Works; and
+
+      (d) If the Work includes a "NOTICE" text file as part of its
+          distribution, then any Derivative Works that You distribute must
+          include a readable copy of the attribution notices contained
+          within such NOTICE file, excluding those notices that do not
+          pertain to any part of the Derivative Works, in at least one
+          of the following places: within a NOTICE text file distributed
+          as part of the Derivative Works; within the Source form or
+          documentation, if provided along with the Derivative Works; or,
+          within a display generated by the Derivative Works, if and
+          wherever such third-party notices normally appear. The contents
+          of the NOTICE file are for informational purposes only and
+          do not modify the License. You may add Your own attribution
+          notices within Derivative Works that You distribute, alongside
+          or as an addendum to the NOTICE text from the Work, provided
+          that such additional attribution notices cannot be construed
+          as modifying the License.
+
+      You may add Your own copyright statement to Your modifications and
+      may provide additional or different license terms and conditions
+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+      implied, including, without limitation, any warranties or conditions
+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
+      incidental, or consequential damages of any character arising as a
+      result of this License or out of the use or inability to use the
+      Work (including but not limited to damages for loss of goodwill,
+      work stoppage, computer failure or malfunction, or any and all
+      other commercial damages or losses), even if such Contributor
+      has been advised of the possibility of such damages.
+
+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
diff --git a/run-as/package.c b/run-as/package.c
new file mode 100644
index 0000000..46f8239
--- /dev/null
+++ b/run-as/package.c
@@ -0,0 +1,471 @@
+/*
+**
+** Copyright 2010, The Android Open Source Project
+**
+** Licensed under the Apache License, Version 2.0 (the "License");
+** you may not use this file except in compliance with the License.
+** You may obtain a copy of the License at
+**
+**     http://www.apache.org/licenses/LICENSE-2.0
+**
+** Unless required by applicable law or agreed to in writing, software
+** distributed under the License is distributed on an "AS IS" BASIS,
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+** See the License for the specific language governing permissions and
+** limitations under the License.
+*/
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <private/android_filesystem_config.h>
+#include "package.h"
+
+/*
+ *  WARNING WARNING WARNING WARNING
+ *
+ *  The following code runs as root on production devices, before
+ *  the run-as command has dropped the uid/gid. Hence be very
+ *  conservative and keep in mind the following:
+ *
+ *  - Performance does not matter here, clarity and safety of the code
+ *    does however. Documentation is a must.
+ *
+ *  - Avoid calling C library functions with complex implementations
+ *    like malloc() and printf(). You want to depend on simple system
+ *    calls instead, which behaviour is not going to be altered in
+ *    unpredictible ways by environment variables or system properties.
+ *
+ *  - Do not trust user input and/or the filesystem whenever possible.
+ *
+ */
+
+/* The file containing the list of installed packages on the system */
+#define PACKAGES_LIST_FILE  "/data/system/packages.list"
+
+/* This should be large enough to hold the content of the package database file */
+#define PACKAGES_LIST_BUFFER_SIZE  8192
+
+/* Copy 'srclen' string bytes from 'src' into buffer 'dst' of size 'dstlen'
+ * This function always zero-terminate the destination buffer unless
+ * 'dstlen' is 0, even in case of overflow.
+ */
+static void
+string_copy(char* dst, size_t dstlen, const char* src, size_t srclen)
+{
+    const char* srcend = src + srclen;
+    const char* dstend = dst + dstlen;
+
+    if (dstlen == 0)
+        return;
+
+    dstend--; /* make room for terminating zero */
+
+    while (dst < dstend && src < srcend && *src != '\0')
+        *dst++ = *src++;
+
+    *dst = '\0'; /* zero-terminate result */
+}
+
+/* Read up to 'buffsize' bytes into 'buff' from the file
+ * named 'filename'. Return byte length on success, or -1
+ * on error.
+ */
+static int
+read_file(const char* filename, char* buff, size_t buffsize)
+{
+    int  fd, len, old_errno;
+
+    /* check the input buffer size */
+    if (buffsize >= INT_MAX) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    /* open the file for reading */
+    do {
+        fd = open(filename, O_RDONLY);
+    } while (fd < 0 && errno == EINTR);
+
+    if (fd < 0)
+        return -1;
+
+    /* read the content */
+    do {
+        len = read(fd, buff, buffsize);
+    } while (len < 0 && errno == EINTR);
+
+    /* close the file, preserve old errno for better diagnostics */
+    old_errno = errno;
+    close(fd);
+    errno = old_errno;
+
+    return len;
+}
+
+/* Check that a given directory:
+ * - exists
+ * - is owned by a given uid/gid
+ * - is a real directory, not a symlink
+ * - isn't readable or writable by others
+ *
+ * Return 0 on success, or -1 on error.
+ * errno is set to EINVAL in case of failed check.
+ */
+static int
+check_directory_ownership(const char* path, uid_t uid)
+{
+    int ret;
+    struct stat st;
+
+    do {
+        ret = lstat(path, &st);
+    } while (ret < 0 && errno == EINTR);
+
+    if (ret < 0)
+        return -1;
+
+    /* must be a real directory, not a symlink */
+    if (!S_ISDIR(st.st_mode))
+        goto BAD;
+
+    /* must be owned by specific uid/gid */
+    if (st.st_uid != uid || st.st_gid != uid)
+        goto BAD;
+
+    /* must not be readable or writable by others */
+    if ((st.st_mode & (S_IROTH|S_IWOTH)) != 0)
+        goto BAD;
+
+    /* everything ok */
+    return 0;
+
+BAD:
+    errno = EINVAL;
+    return -1;
+}
+
+/* This function is used to check the data directory path for safety.
+ * We check that every sub-directory is owned by the 'system' user
+ * and exists and is not a symlink. We also check that the full directory
+ * path is properly owned by the user ID.
+ *
+ * Return 0 on success, -1 on error.
+ */
+int
+check_data_path(const char* dataPath, uid_t  uid)
+{
+    int  nn;
+
+    /* the path should be absolute */
+    if (dataPath[0] != '/') {
+        errno = EINVAL;
+        return -1;
+    }
+
+    /* look for all sub-paths, we do that by finding
+     * directory separators in the input path and
+     * checking each sub-path independently
+     */
+    for (nn = 1; dataPath[nn] != '\0'; nn++)
+    {
+        char subpath[PATH_MAX];
+
+        /* skip non-separator characters */
+        if (dataPath[nn] != '/')
+            continue;
+
+        /* handle trailing separator case */
+        if (dataPath[nn+1] == '\0') {
+            break;
+        }
+
+        /* found a separator, check that dataPath is not too long. */
+        if (nn >= (int)(sizeof subpath)) {
+            errno = EINVAL;
+            return -1;
+        }
+
+        /* reject any '..' subpath */
+        if (nn >= 3               &&
+            dataPath[nn-3] == '/' &&
+            dataPath[nn-2] == '.' &&
+            dataPath[nn-1] == '.') {
+            errno = EINVAL;
+            return -1;
+        }
+
+        /* copy to 'subpath', then check ownership */
+        memcpy(subpath, dataPath, nn);
+        subpath[nn] = '\0';
+
+        if (check_directory_ownership(subpath, AID_SYSTEM) < 0)
+            return -1;
+    }
+
+    /* All sub-paths were checked, now verify that the full data
+     * directory is owned by the application uid
+     */
+    if (check_directory_ownership(dataPath, uid) < 0)
+        return -1;
+
+    /* all clear */
+    return 0;
+}
+
+/* Return TRUE iff a character is a space or tab */
+static inline int
+is_space(char c)
+{
+    return (c == ' ' || c == '\t');
+}
+
+/* Skip any space or tab character from 'p' until 'end' is reached.
+ * Return new position.
+ */
+static const char*
+skip_spaces(const char*  p, const char*  end)
+{
+    while (p < end && is_space(*p))
+        p++;
+
+    return p;
+}
+
+/* Skip any non-space and non-tab character from 'p' until 'end'.
+ * Return new position.
+ */
+static const char*
+skip_non_spaces(const char* p, const char* end)
+{
+    while (p < end && !is_space(*p))
+        p++;
+
+    return p;
+}
+
+/* Find the first occurence of 'ch' between 'p' and 'end'
+ * Return its position, or 'end' if none is found.
+ */
+static const char*
+find_first(const char* p, const char* end, char ch)
+{
+    while (p < end && *p != ch)
+        p++;
+
+    return p;
+}
+
+/* Check that the non-space string starting at 'p' and eventually
+ * ending at 'end' equals 'name'. Return new position (after name)
+ * on success, or NULL on failure.
+ *
+ * This function fails is 'name' is NULL, empty or contains any space.
+ */
+static const char*
+compare_name(const char* p, const char* end, const char* name)
+{
+    /* 'name' must not be NULL or empty */
+    if (name == NULL || name[0] == '\0' || p == end)
+        return NULL;
+
+    /* compare characters to those in 'name', excluding spaces */
+    while (*name) {
+        /* note, we don't check for *p == '\0' since
+         * it will be caught in the next conditional.
+         */
+        if (p >= end || is_space(*p))
+            goto BAD;
+
+        if (*p != *name)
+            goto BAD;
+
+        p++;
+        name++;
+    }
+
+    /* must be followed by end of line or space */
+    if (p < end && !is_space(*p))
+        goto BAD;
+
+    return p;
+
+BAD:
+    return NULL;
+}
+
+/* Parse one or more whitespace characters starting from '*pp'
+ * until 'end' is reached. Updates '*pp' on exit.
+ *
+ * Return 0 on success, -1 on failure.
+ */
+static int
+parse_spaces(const char** pp, const char* end)
+{
+    const char* p = *pp;
+
+    if (p >= end || !is_space(*p)) {
+        errno = EINVAL;
+        return -1;
+    }
+    p   = skip_spaces(p, end);
+    *pp = p;
+    return 0;
+}
+
+/* Parse a positive decimal number starting from '*pp' until 'end'
+ * is reached. Adjust '*pp' on exit. Return decimal value or -1
+ * in case of error.
+ *
+ * If the value is larger than INT_MAX, -1 will be returned,
+ * and errno set to EOVERFLOW.
+ *
+ * If '*pp' does not start with a decimal digit, -1 is returned
+ * and errno set to EINVAL.
+ */
+static int
+parse_positive_decimal(const char** pp, const char* end)
+{
+    const char* p = *pp;
+    int value = 0;
+    int overflow = 0;
+
+    if (p >= end || *p < '0' || *p > '9') {
+        errno = EINVAL;
+        return -1;
+    }
+
+    while (p < end) {
+        int      ch = *p;
+        unsigned d  = (unsigned)(ch - '0');
+        int      val2;
+
+        if (d >= 10U) /* d is unsigned, no lower bound check */
+            break;
+
+        val2 = value*10 + (int)d;
+        if (val2 < value)
+            overflow = 1;
+        value = val2;
+        p++;
+    }
+    *pp = p;
+
+    if (overflow) {
+        errno = EOVERFLOW;
+        value = -1;
+    }
+    return value;
+
+BAD:
+    *pp = p;
+    return -1;
+}
+
+/* Read the system's package database and extract information about
+ * 'pkgname'. Return 0 in case of success, or -1 in case of error.
+ *
+ * If the package is unknown, return -1 and set errno to ENOENT
+ * If the package database is corrupted, return -1 and set errno to EINVAL
+ */
+int
+get_package_info(const char* pkgName, PackageInfo *info)
+{
+    static char  buffer[PACKAGES_LIST_BUFFER_SIZE];
+    int          buffer_len;
+    const char*  p;
+    const char*  buffer_end;
+    int          result;
+
+    info->uid          = 0;
+    info->isDebuggable = 0;
+    info->dataDir[0]   = '\0';
+
+    buffer_len = read_file(PACKAGES_LIST_FILE, buffer, sizeof buffer);
+    if (buffer_len < 0)
+        return -1;
+
+    p          = buffer;
+    buffer_end = buffer + buffer_len;
+
+    /* expect the following format on each line of the control file:
+     *
+     *  <pkgName> <uid> <debugFlag> <dataDir>
+     *
+     * where:
+     *  <pkgName>    is the package's name
+     *  <uid>        is the application-specific user Id (decimal)
+     *  <debugFlag>  is 1 if the package is debuggable, or 0 otherwise
+     *  <dataDir>    is the path to the package's data directory (e.g. /data/data/com.example.foo)
+     *
+     * The file is generated in com.android.server.PackageManagerService.Settings.writeLP()
+     */
+
+    while (p < buffer_end) {
+        /* find end of current line and start of next one */
+        const char*  end  = find_first(p, buffer_end, '\n');
+        const char*  next = (end < buffer_end) ? end + 1 : buffer_end;
+        const char*  q;
+        int          uid, debugFlag;
+
+        /* first field is the package name */
+        p = compare_name(p, end, pkgName);
+        if (p == NULL)
+            goto NEXT_LINE;
+
+        /* skip spaces */
+        if (parse_spaces(&p, end) < 0)
+            goto BAD_FORMAT;
+
+        /* second field is the pid */
+        uid = parse_positive_decimal(&p, end);
+        if (uid < 0)
+            return -1;
+
+        info->uid = (uid_t) uid;
+
+        /* skip spaces */
+        if (parse_spaces(&p, end) < 0)
+            goto BAD_FORMAT;
+
+        /* third field is debug flag (0 or 1) */
+        debugFlag = parse_positive_decimal(&p, end);
+        switch (debugFlag) {
+        case 0:
+            info->isDebuggable = 0;
+            break;
+        case 1:
+            info->isDebuggable = 1;
+            break;
+        default:
+            goto BAD_FORMAT;
+        }
+
+        /* skip spaces */
+        if (parse_spaces(&p, end) < 0)
+            goto BAD_FORMAT;
+
+        /* fourth field is data directory path and must not contain
+         * spaces.
+         */
+        q = skip_non_spaces(p, end);
+        if (q == p)
+            goto BAD_FORMAT;
+
+        string_copy(info->dataDir, sizeof info->dataDir, p, q - p);
+
+        /* Ignore the rest */
+        return 0;
+
+    NEXT_LINE:
+        p = next;
+    }
+
+    /* the package is unknown */
+    errno = ENOENT;
+    return -1;
+
+BAD_FORMAT:
+    errno = EINVAL;
+    return -1;
+}
diff --git a/run-as/package.h b/run-as/package.h
new file mode 100644
index 0000000..852af06
--- /dev/null
+++ b/run-as/package.h
@@ -0,0 +1,41 @@
+/*
+**
+** Copyright 2010, The Android Open Source Project
+**
+** Licensed under the Apache License, Version 2.0 (the "License");
+** you may not use this file except in compliance with the License.
+** You may obtain a copy of the License at
+**
+**     http://www.apache.org/licenses/LICENSE-2.0
+**
+** Unless required by applicable law or agreed to in writing, software
+** distributed under the License is distributed on an "AS IS" BASIS,
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+** See the License for the specific language governing permissions and
+** limitations under the License.
+*/
+#ifndef RUN_AS_PACKAGE_H
+#define RUN_AS_PACKAGE_H
+
+#include <limits.h>
+#include <sys/types.h>
+
+typedef enum {
+    PACKAGE_IS_DEBUGGABLE = 0,
+    PACKAGE_IS_NOT_DEBUGGABLE,
+    PACKAGE_IS_UNKNOWN,
+} PackageStatus;
+
+typedef struct {
+    uid_t  uid;
+    char   isDebuggable;
+    char   dataDir[PATH_MAX];
+} PackageInfo;
+
+/* see documentation in package.c for these functiosn */
+
+extern int  get_package_info(const char* packageName, PackageInfo*  info);
+
+extern int  check_data_path(const char* dataDir, uid_t uid);
+
+#endif /* RUN_AS_PACKAGE_H */
diff --git a/run-as/run-as.c b/run-as/run-as.c
new file mode 100644
index 0000000..d2a44e1
--- /dev/null
+++ b/run-as/run-as.c
@@ -0,0 +1,178 @@
+/*
+**
+** Copyright 2010, The Android Open Source Project
+**
+** Licensed under the Apache License, Version 2.0 (the "License");
+** you may not use this file except in compliance with the License.
+** You may obtain a copy of the License at
+**
+**     http://www.apache.org/licenses/LICENSE-2.0
+**
+** Unless required by applicable law or agreed to in writing, software
+** distributed under the License is distributed on an "AS IS" BASIS,
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+** See the License for the specific language governing permissions and
+** limitations under the License.
+*/
+
+#define PROGNAME  "run-as"
+#define LOG_TAG   PROGNAME
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <dirent.h>
+#include <errno.h>
+#include <unistd.h>
+#include <time.h>
+#include <stdarg.h>
+
+#include <private/android_filesystem_config.h>
+#include "package.h"
+
+/*
+ *  WARNING WARNING WARNING WARNING
+ *
+ *  This program runs as set-uid root on Android production devices.
+ *  Be very conservative when modifying it to avoid any serious
+ *  security issue. Keep in mind the following:
+ *
+ *  - This program should only run for the 'root' or 'shell' users
+ *
+ *  - Statically link against the C library, and avoid anything that
+ *    is more complex than simple system calls until the uid/gid has
+ *    been dropped to that of a normal user or you are sure to exit.
+ *
+ *    This avoids depending on environment variables, system properties
+ *    and other external factors that may affect the C library in
+ *    unpredictable ways.
+ *
+ *  - Do not trust user input and/or the filesystem whenever possible.
+ *
+ *  Read README.TXT for more details.
+ *
+ *
+ *
+ * The purpose of this program is to run a command as a specific
+ * application user-id. Typical usage is:
+ *
+ *   run-as <package-name> <command> <args>
+ *
+ *  The 'run-as' binary is setuid, but will check the following:
+ *
+ *  - that it is invoked from the 'shell' or 'root' user (abort otherwise)
+ *  - that '<package-name>' is the name of an installed and debuggable package
+ *  - that the package's data directory is well-formed (see package.c)
+ *
+ *  If so, it will cd to the package's data directory, drop to the application's
+ *  user id / group id then run the command there.
+ *
+ *  This can be useful for a number of different things on production devices:
+ *
+ *  - Allow application developers to look at their own applicative data
+ *    during development.
+ *
+ *  - Run the 'gdbserver' binary executable to allow native debugging
+ */
+
+static void
+usage(void)
+{
+    const char*  str = "Usage: " PROGNAME " <package-name> <command> [<args>]\n\n";
+    write(1, str, strlen(str));
+    exit(1);
+}
+
+
+static void
+panic(const char* format, ...)
+{
+    va_list args;
+
+    fprintf(stderr, "%s: ", PROGNAME);
+    va_start(args, format);
+    vfprintf(stderr, format, args);
+    va_end(args);
+    exit(1);
+}
+
+
+int main(int argc, char **argv)
+{
+    const char* pkgname;
+    int myuid, uid, gid;
+    PackageInfo info;
+
+    /* check arguments */
+    if (argc < 2)
+        usage();
+
+    /* check userid of caller - must be 'shell' or 'root' */
+    myuid = getuid();
+    if (myuid != AID_SHELL && myuid != AID_ROOT) {
+        panic("only 'shell' or 'root' users can run this program\n");
+    }
+
+    /* retrieve package information from system */
+    pkgname = argv[1];
+    if (get_package_info(pkgname, &info) < 0) {
+        panic("Package '%s' is unknown\n", pkgname);
+        return 1;
+    }
+
+    /* reject system packages */
+    if (info.uid < AID_APP) {
+        panic("Package '%s' is not an application\n", pkgname);
+        return 1;
+    }
+
+    /* reject any non-debuggable package */
+    if (!info.isDebuggable) {
+        panic("Package '%s' is not debuggable\n", pkgname);
+        return 1;
+    }
+
+    /* check that the data directory path is valid */
+    if (check_data_path(info.dataDir, info.uid) < 0) {
+        panic("Package '%s' has corrupt installation\n", pkgname);
+        return 1;
+    }
+
+    /* then move to it */
+    {
+        int ret;
+        do {
+            ret = chdir(info.dataDir);
+        } while (ret < 0 && errno == EINTR);
+
+        if (ret < 0) {
+            panic("Could not cd to package's data directory: %s\n", strerror(errno));
+            return 1;
+        }
+    }
+
+    /* Ensure that we change all real/effective/saved IDs at the
+     * same time to avoid nasty surprises.
+     */
+    uid = gid = info.uid;
+    if(setresgid(gid,gid,gid) || setresuid(uid,uid,uid)) {
+        panic("Permission denied\n");
+        return 1;
+    }
+
+    /* User specified command for exec. */
+    if (argc >= 3 ) {
+        if (execvp(argv[2], argv+2) < 0) {
+            panic("exec failed for %s Error:%s\n", argv[2], strerror(errno));
+            return -errno;
+        }
+    }
+
+    /* Default exec shell. */
+    execlp("/system/bin/sh", "sh", NULL);
+
+    panic("exec failed\n");
+    return 1;
+}