sideload without holding the whole package in RAM

Implement a new method of sideloading over ADB that does not require
the entire package to be held in RAM (useful for low-RAM devices and
devices using block OTA where we'd rather have more RAM available for
binary patching).

We communicate with the host using a new adb service called
"sideload-host", which makes the host act as a server, sending us
different parts of the package file on request.

We create a FUSE filesystem that creates a virtual file
"/sideload/package.zip" that is backed by the ADB connection -- users
see a normal file, but when they read from the file we're actually
fetching the data from the adb host.  This file is then passed to the
verification and installation systems like any other.

To prevent a malicious adb host implementation from serving different
data to the verification and installation phases of sideloading, the
FUSE filesystem verifies that the contents of the file don't change
between reads -- every time we fetch a block from the host we compare
its hash to the previous hash for that block (if it was read before)
and cause the read to fail if it changes.

One necessary change is that the minadbd started by recovery in
sideload mode no longer drops its root privileges (they're needed to
mount the FUSE filesystem).  We rely on SELinux enforcement to
restrict the set of things that can be accessed.

Change-Id: Ida7dbd3b04c1d4e27a2779d88c1da0c7c81fb114

6 files changed, 557 insertions, 48 deletions

diff --git a/minadbd/Android.mk b/minadbd/Android.mk
index 5a4de68..b5fb844 100644
--- a/minadbd/Android.mk
+++ b/minadbd/Android.mk
@@ -13,6 +13,7 @@ include $(CLEAR_VARS)
 LOCAL_SRC_FILES := \
 	adb.c \
 	fdevent.c \
+	fuse_sideload.c \
 	transport.c \
 	transport_usb.c \
 	sockets.c \
@@ -25,8 +26,5 @@ LOCAL_CFLAGS += -D_XOPEN_SOURCE -D_GNU_SOURCE
 
 LOCAL_MODULE := libminadbd
 
-LOCAL_STATIC_LIBRARIES := libcutils libc
+LOCAL_STATIC_LIBRARIES := libcutils libc libmincrypt
 include $(BUILD_STATIC_LIBRARY)
-
-
-
diff --git a/minadbd/adb.c b/minadbd/adb.c
index 7291b4b..127d072 100644
--- a/minadbd/adb.c
+++ b/minadbd/adb.c
@@ -392,16 +392,6 @@ int adb_main()
         usb_init();
     }
 
-    if (setgid(AID_SHELL) != 0) {
-        fprintf(stderr, "failed to setgid to shell\n");
-        exit(1);
-    }
-    if (setuid(AID_SHELL) != 0) {
-        fprintf(stderr, "failed to setuid to shell\n");
-        exit(1);
-    }
-    fprintf(stderr, "userid is %d\n", getuid());
-
     D("Event loop starting\n");
 
     fdevent_loop();
diff --git a/minadbd/adb.h b/minadbd/adb.h
index d389165..770f34d 100644
--- a/minadbd/adb.h
+++ b/minadbd/adb.h
@@ -400,6 +400,7 @@ int connection_state(atransport *t);
 #define CS_RECOVERY   4
 #define CS_NOPERM     5 /* Insufficient permissions to communicate with the device */
 #define CS_SIDELOAD   6
+#define CS_UNAUTHORIZED 7
 
 extern int HOST;
 extern int SHELL_EXIT_NOTIFY_FD;
@@ -420,6 +421,11 @@ extern int SHELL_EXIT_NOTIFY_FD;
 int sendfailmsg(int fd, const char *reason);
 int handle_host_request(char *service, transport_type ttype, char* serial, int reply_fd, asocket *s);
 
-#define ADB_SIDELOAD_FILENAME "/tmp/update.zip"
+// define the filenames created by the sideload-host FUSE filesystem
+#define ADB_SIDELOAD_HOST_MOUNTPOINT "/sideload"
+#define ADB_SIDELOAD_HOST_FILENAME "package.zip"
+#define ADB_SIDELOAD_HOST_PATHNAME (ADB_SIDELOAD_HOST_MOUNTPOINT "/" ADB_SIDELOAD_HOST_FILENAME)
+#define ADB_SIDELOAD_HOST_EXIT_FLAG "exit"
+#define ADB_SIDELOAD_HOST_EXIT_PATHNAME (ADB_SIDELOAD_HOST_MOUNTPOINT "/" ADB_SIDELOAD_HOST_EXIT_FLAG)
 
 #endif
diff --git a/minadbd/fuse_sideload.c b/minadbd/fuse_sideload.c
new file mode 100644
index 0000000..def068e
--- /dev/null
+++ b/minadbd/fuse_sideload.c
@@ -0,0 +1,508 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+// This module creates a special filesystem containing two files.
+//
+// "/sideload/package.zip" appears to be a normal file, but reading
+// from it causes data to be fetched from the adb host.  We can use
+// this to sideload packages over an adb connection without having to
+// store the entire package in RAM on the device.
+//
+// Because we may not trust the adb host, this filesystem maintains
+// the following invariant: each read of a given position returns the
+// same data as the first read at that position.  That is, once a
+// section of the file is read, future reads of that section return
+// the same data.  (Otherwise, a malicious adb host process could
+// return one set of bits when the package is read for signature
+// verification, and then different bits for when the package is
+// accessed by the installer.)  If the adb host returns something
+// different than it did on the first read, the reader of the file
+// will see their read fail with EINVAL.
+//
+// The other file, "/sideload/exit", is used to control the subprocess
+// that creates this filesystem.  Calling stat() on the exit file
+// causes the filesystem to be unmounted and the adb process on the
+// device shut down.
+//
+// Note that only the minimal set of file operations needed for these
+// two files is implemented.  In particular, you can't opendir() or
+// readdir() on the "/sideload" directory; ls on it won't work.
+
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <linux/fuse.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/inotify.h>
+#include <sys/mount.h>
+#include <sys/resource.h>
+#include <sys/stat.h>
+#include <sys/statfs.h>
+#include <sys/time.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+#include "transport.h"
+#include "adb.h"
+#include "mincrypt/sha256.h"
+
+#define PACKAGE_FILE_ID   (FUSE_ROOT_ID+1)
+#define EXIT_FLAG_ID      (FUSE_ROOT_ID+2)
+
+#define NO_STATUS         1
+#define NO_STATUS_EXIT    2
+
+struct fuse_data {
+    int ffd;   // file descriptor for the fuse socket
+    int sfd;   // file descriptor for the adb channel
+
+    uint64_t file_size;     // bytes
+
+    uint32_t block_size;    // block size that the adb host is using to send the file to us
+    uint32_t file_blocks;   // file size in block_size blocks
+
+    uid_t uid;
+    gid_t gid;
+
+    uint32_t curr_block;    // cache the block most recently read from the host
+    uint8_t* block_data;
+
+    uint8_t* extra_block;   // another block of storage for reads that
+                            // span two blocks
+
+    uint8_t* hashes;        // SHA-256 hash of each block (all zeros
+                            // if block hasn't been read yet)
+};
+
+static void fuse_reply(struct fuse_data* fd, __u64 unique, const void *data, size_t len)
+{
+    struct fuse_out_header hdr;
+    struct iovec vec[2];
+    int res;
+
+    hdr.len = len + sizeof(hdr);
+    hdr.error = 0;
+    hdr.unique = unique;
+
+    vec[0].iov_base = &hdr;
+    vec[0].iov_len = sizeof(hdr);
+    vec[1].iov_base = data;
+    vec[1].iov_len = len;
+
+    res = writev(fd->ffd, vec, 2);
+    if (res < 0) {
+        printf("*** REPLY FAILED *** %d\n", errno);
+    }
+}
+
+static int handle_init(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
+    const struct fuse_init_in* req = data;
+    struct fuse_init_out out;
+
+    out.major = FUSE_KERNEL_VERSION;
+    out.minor = FUSE_KERNEL_MINOR_VERSION;
+    out.max_readahead = req->max_readahead;
+    out.flags = 0;
+    out.max_background = 32;
+    out.congestion_threshold = 32;
+    out.max_write = 4096;
+    fuse_reply(fd, hdr->unique, &out, sizeof(out));
+
+    return NO_STATUS;
+}
+
+static void fill_attr(struct fuse_attr* attr, struct fuse_data* fd,
+                      uint64_t nodeid, uint64_t size, uint32_t mode) {
+    memset(attr, 0, sizeof(*attr));
+    attr->nlink = 1;
+    attr->uid = fd->uid;
+    attr->gid = fd->gid;
+    attr->blksize = 4096;
+
+    attr->ino = nodeid;
+    attr->size = size;
+    attr->blocks = (size == 0) ? 0 : (((size-1) / attr->blksize) + 1);
+    attr->mode = mode;
+}
+
+static int handle_getattr(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
+    const struct fuse_getattr_in* req = data;
+    struct fuse_attr_out out;
+    memset(&out, 0, sizeof(out));
+    out.attr_valid = 10;
+
+    if (hdr->nodeid == FUSE_ROOT_ID) {
+        fill_attr(&(out.attr), fd, hdr->nodeid, 4096, S_IFDIR | 0555);
+    } else if (hdr->nodeid == PACKAGE_FILE_ID) {
+        fill_attr(&(out.attr), fd, PACKAGE_FILE_ID, fd->file_size, S_IFREG | 0444);
+    } else if (hdr->nodeid == EXIT_FLAG_ID) {
+        fill_attr(&(out.attr), fd, EXIT_FLAG_ID, 0, S_IFREG | 0);
+    } else {
+        return -ENOENT;
+    }
+
+    fuse_reply(fd, hdr->unique, &out, sizeof(out));
+    return (hdr->nodeid == EXIT_FLAG_ID) ? NO_STATUS_EXIT : NO_STATUS;
+}
+
+static int handle_lookup(void* data, struct fuse_data* fd,
+                         const struct fuse_in_header* hdr) {
+    struct fuse_entry_out out;
+    memset(&out, 0, sizeof(out));
+    out.entry_valid = 10;
+    out.attr_valid = 10;
+
+    if (strncmp(ADB_SIDELOAD_HOST_FILENAME, data,
+                sizeof(ADB_SIDELOAD_HOST_FILENAME)) == 0) {
+        out.nodeid = PACKAGE_FILE_ID;
+        out.generation = PACKAGE_FILE_ID;
+        fill_attr(&(out.attr), fd, PACKAGE_FILE_ID, fd->file_size, S_IFREG | 0444);
+    } else if (strncmp(ADB_SIDELOAD_HOST_EXIT_FLAG, data,
+                       sizeof(ADB_SIDELOAD_HOST_EXIT_FLAG)) == 0) {
+        out.nodeid = EXIT_FLAG_ID;
+        out.generation = EXIT_FLAG_ID;
+        fill_attr(&(out.attr), fd, EXIT_FLAG_ID, 0, S_IFREG | 0);
+    } else {
+        return -ENOENT;
+    }
+
+    fuse_reply(fd, hdr->unique, &out, sizeof(out));
+    return (out.nodeid == EXIT_FLAG_ID) ? NO_STATUS_EXIT : NO_STATUS;
+}
+
+static int handle_open(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
+    const struct fuse_open_in* req = data;
+
+    if (hdr->nodeid == EXIT_FLAG_ID) return -EPERM;
+    if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT;
+
+    struct fuse_open_out out;
+    memset(&out, 0, sizeof(out));
+    out.fh = 10;  // an arbitrary number; we always use the same handle
+    fuse_reply(fd, hdr->unique, &out, sizeof(out));
+    return NO_STATUS;
+}
+
+static int handle_flush(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
+    return 0;
+}
+
+static int handle_release(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
+    return 0;
+}
+
+// Fetch a block from the host into fd->curr_block and fd->block_data.
+// Returns 0 on successful fetch, negative otherwise.
+static int fetch_block(struct fuse_data* fd, uint32_t block) {
+    if (block == fd->curr_block) {
+        return 0;
+    }
+
+    if (block >= fd->file_blocks) {
+        memset(fd->block_data, 0, fd->block_size);
+        fd->curr_block = block;
+        return 0;
+    }
+
+    size_t fetch_size = fd->block_size;
+    if (block * fd->block_size + fetch_size > fd->file_size) {
+        // If we're reading the last (partial) block of the file,
+        // expect a shorter response from the host, and pad the rest
+        // of the block with zeroes.
+        fetch_size = fd->file_size - (block * fd->block_size);
+        memset(fd->block_data + fetch_size, 0, fd->block_size - fetch_size);
+    }
+
+    char buf[10];
+    snprintf(buf, sizeof(buf), "%08u", block);
+    if (writex(fd->sfd, buf, 8) < 0) {
+        fprintf(stderr, "failed to write to adb host: %s\n", strerror(errno));
+        return -EIO;
+    }
+
+    if (readx(fd->sfd, fd->block_data, fetch_size) < 0) {
+        fprintf(stderr, "failed to read from adb host: %s\n", strerror(errno));
+        return -EIO;
+    }
+
+    fd->curr_block = block;
+
+    // Verify the hash of the block we just got from the host.
+    //
+    // - If the hash of the just-received data matches the stored hash
+    //   for the block, accept it.
+    // - If the stored hash is all zeroes, store the new hash and
+    //   accept the block (this is the first time we've read this
+    //   block).
+    // - Otherwise, return -EINVAL for the read.
+
+    uint8_t hash[SHA256_DIGEST_SIZE];
+    SHA256_hash(fd->block_data, fd->block_size, hash);
+    uint8_t* blockhash = fd->hashes + block * SHA256_DIGEST_SIZE;
+    if (memcmp(hash, blockhash, SHA256_DIGEST_SIZE) == 0) {
+        return 0;
+    }
+
+    int i;
+    for (i = 0; i < SHA256_DIGEST_SIZE; ++i) {
+        if (blockhash[i] != 0) {
+            fd->curr_block = -1;
+            return -EIO;
+        }
+    }
+
+    memcpy(blockhash, hash, SHA256_DIGEST_SIZE);
+    return 0;
+}
+
+static int handle_read(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) {
+    const struct fuse_read_in* req = data;
+    struct fuse_out_header outhdr;
+    struct iovec vec[3];
+    int vec_used;
+    int result;
+
+    if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT;
+
+    uint64_t offset = req->offset;
+    uint32_t size = req->size;
+
+    // The docs on the fuse kernel interface are vague about what to
+    // do when a read request extends past the end of the file.  We
+    // can return a short read -- the return structure does include a
+    // length field -- but in testing that caused the program using
+    // the file to segfault.  (I speculate that this is due to the
+    // reading program accessing it via mmap; maybe mmap dislikes when
+    // you return something short of a whole page?)  To fix this we
+    // zero-pad reads that extend past the end of the file so we're
+    // always returning exactly as many bytes as were requested.
+    // (Users of the mapped file have to know its real length anyway.)
+
+    outhdr.len = sizeof(outhdr) + size;
+    outhdr.error = 0;
+    outhdr.unique = hdr->unique;
+    vec[0].iov_base = &outhdr;
+    vec[0].iov_len = sizeof(outhdr);
+
+    uint32_t block = offset / fd->block_size;
+    result = fetch_block(fd, block);
+    if (result != 0) return result;
+
+    // Two cases:
+    //
+    //   - the read request is entirely within this block.  In this
+    //     case we can reply immediately.
+    //
+    //   - the read request goes over into the next block.  Note that
+    //     since we mount the filesystem with max_read=block_size, a
+    //     read can never span more than two blocks.  In this case we
+    //     copy the block to extra_block and issue a fetch for the
+    //     following block.
+
+    uint32_t block_offset = offset - (block * fd->block_size);
+
+    if (size + block_offset <= fd->block_size) {
+        // First case: the read fits entirely in the first block.
+
+        vec[1].iov_base = fd->block_data + block_offset;
+        vec[1].iov_len = size;
+        vec_used = 2;
+    } else {
+        // Second case: the read spills over into the next block.
+
+        memcpy(fd->extra_block, fd->block_data + block_offset,
+               fd->block_size - block_offset);
+        vec[1].iov_base = fd->extra_block;
+        vec[1].iov_len = fd->block_size - block_offset;
+
+        result = fetch_block(fd, block+1);
+        if (result != 0) return result;
+        vec[2].iov_base = fd->block_data;
+        vec[2].iov_len = size - vec[1].iov_len;
+        vec_used = 3;
+    }
+
+    if (writev(fd->ffd, vec, vec_used) < 0) {
+        printf("*** READ REPLY FAILED: %s ***\n", strerror(errno));
+    }
+    return NO_STATUS;
+}
+
+int run_fuse(int sfd, uint64_t file_size, uint32_t block_size)
+{
+    int result;
+
+    // If something's already mounted on our mountpoint, try to remove
+    // it.  (Mostly in case of a previous abnormal exit.)
+    umount2(ADB_SIDELOAD_HOST_MOUNTPOINT, MNT_FORCE);
+
+    if (block_size < 1024) {
+        fprintf(stderr, "block size (%u) is too small\n", block_size);
+        return -1;
+    }
+    if (block_size > (1<<22)) {   // 4 MiB
+        fprintf(stderr, "block size (%u) is too large\n", block_size);
+        return -1;
+    }
+
+    struct fuse_data fd;
+    memset(&fd, 0, sizeof(fd));
+    fd.sfd = sfd;
+    fd.file_size = file_size;
+    fd.block_size = block_size;
+    fd.file_blocks = (file_size == 0) ? 0 : (((file_size-1) / block_size) + 1);
+
+    if (fd.file_blocks > (1<<18)) {
+        fprintf(stderr, "file has too many blocks (%u)\n", fd.file_blocks);
+        result = -1;
+        goto done;
+    }
+
+    fd.hashes = (uint8_t*)calloc(fd.file_blocks, SHA256_DIGEST_SIZE);
+    if (fd.hashes == NULL) {
+        fprintf(stderr, "failed to allocate %d bites for hashes\n",
+                fd.file_blocks * SHA256_DIGEST_SIZE);
+        result = -1;
+        goto done;
+    }
+
+    fd.uid = getuid();
+    fd.gid = getgid();
+
+    fd.curr_block = -1;
+    fd.block_data = (uint8_t*)malloc(block_size);
+    if (fd.block_data == NULL) {
+        fprintf(stderr, "failed to allocate %d bites for block_data\n", block_size);
+        result = -1;
+        goto done;
+    }
+    fd.extra_block = (uint8_t*)malloc(block_size);
+    if (fd.extra_block == NULL) {
+        fprintf(stderr, "failed to allocate %d bites for extra_block\n", block_size);
+        result = -1;
+        goto done;
+    }
+
+    fd.ffd = open("/dev/fuse", O_RDWR);
+    if (fd.ffd < 0) {
+        perror("open /dev/fuse");
+        result = -1;
+        goto done;
+    }
+
+    char opts[256];
+    snprintf(opts, sizeof(opts),
+             ("fd=%d,user_id=%d,group_id=%d,max_read=%zu,"
+              "allow_other,rootmode=040000"),
+             fd.ffd, fd.uid, fd.gid, block_size);
+
+    result = mount("/dev/fuse", ADB_SIDELOAD_HOST_MOUNTPOINT,
+                   "fuse", MS_NOSUID | MS_NODEV | MS_RDONLY | MS_NOEXEC, opts);
+    if (result < 0) {
+        perror("mount");
+        goto done;
+    }
+    uint8_t request_buffer[sizeof(struct fuse_in_header) + PATH_MAX*8];
+    for (;;) {
+        ssize_t len = read(fd.ffd, request_buffer, sizeof(request_buffer));
+        if (len < 0) {
+            if (errno != EINTR) {
+                perror("read request");
+                if (errno == ENODEV) {
+                    result = -1;
+                    break;
+                }
+            }
+            continue;
+        }
+
+        if ((size_t)len < sizeof(struct fuse_in_header)) {
+            fprintf(stderr, "request too short: len=%zu\n", (size_t)len);
+            continue;
+        }
+
+        struct fuse_in_header* hdr = (struct fuse_in_header*) request_buffer;
+        void* data = request_buffer + sizeof(struct fuse_in_header);
+
+        result = -ENOSYS;
+
+        switch (hdr->opcode) {
+             case FUSE_INIT:
+                result = handle_init(data, &fd, hdr);
+                break;
+
+             case FUSE_LOOKUP:
+                result = handle_lookup(data, &fd, hdr);
+                break;
+
+            case FUSE_GETATTR:
+                result = handle_getattr(data, &fd, hdr);
+                break;
+
+            case FUSE_OPEN:
+                result = handle_open(data, &fd, hdr);
+                break;
+
+            case FUSE_READ:
+                result = handle_read(data, &fd, hdr);
+                break;
+
+            case FUSE_FLUSH:
+                result = handle_flush(data, &fd, hdr);
+                break;
+
+            case FUSE_RELEASE:
+                result = handle_release(data, &fd, hdr);
+                break;
+
+            default:
+                fprintf(stderr, "unknown fuse request opcode %d\n", hdr->opcode);
+                break;
+        }
+
+        if (result == NO_STATUS_EXIT) {
+            result = 0;
+            break;
+        }
+
+        if (result != NO_STATUS) {
+            struct fuse_out_header outhdr;
+            outhdr.len = sizeof(outhdr);
+            outhdr.error = result;
+            outhdr.unique = hdr->unique;
+            write(fd.ffd, &outhdr, sizeof(outhdr));
+        }
+    }
+
+  done:
+    writex(sfd, "DONEDONE", 8);
+    result = umount2(ADB_SIDELOAD_HOST_MOUNTPOINT, MNT_DETACH);
+    if (result < 0) {
+        printf("fuse_sideload umount failed: %s\n", strerror(errno));
+    }
+
+    if (fd.ffd) close(fd.ffd);
+    free(fd.hashes);
+    free(fd.block_data);
+    free(fd.extra_block);
+
+    return result;
+}
diff --git a/minadbd/fuse_sideload.h b/minadbd/fuse_sideload.h
new file mode 100644
index 0000000..caeeec7
--- /dev/null
+++ b/minadbd/fuse_sideload.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2014 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 __FUSE_SIDELOAD_H
+#define __FUSE_SIDELOAD_H
+
+int run_fuse(int sfd, uint64_t file_size, uint32_t block_size);
+
+#endif
diff --git a/minadbd/services.c b/minadbd/services.c
index 752b33e..bf57dc3 100644
--- a/minadbd/services.c
+++ b/minadbd/services.c
@@ -22,6 +22,7 @@
 
 #include "sysdeps.h"
 #include "fdevent.h"
+#include "fuse_sideload.h"
 
 #define  TRACE_TAG  TRACE_SERVICES
 #include "adb.h"
@@ -43,44 +44,23 @@ void *service_bootstrap_func(void *x)
     return 0;
 }
 
-static void sideload_service(int s, void *cookie)
+static void sideload_host_service(int sfd, void* cookie)
 {
-    unsigned char buf[4096];
-    unsigned count = (unsigned)(uintptr_t)cookie;
-    int fd;
-
-    fprintf(stderr, "sideload_service invoked\n");
-
-    fd = adb_creat(ADB_SIDELOAD_FILENAME, 0644);
-    if(fd < 0) {
-        fprintf(stderr, "failed to create %s\n", ADB_SIDELOAD_FILENAME);
-        adb_close(s);
-        exit(1);
-    }
+    char* saveptr;
+    const char* s = strtok_r(cookie, ":", &saveptr);
+    uint64_t file_size = strtoull(s, NULL, 10);
+    s = strtok_r(NULL, ":", &saveptr);
+    uint32_t block_size = strtoul(s, NULL, 10);
 
-    while(count > 0) {
-        unsigned xfer = (count > 4096) ? 4096 : count;
-        if(readx(s, buf, xfer)) break;
-        if(writex(fd, buf, xfer)) break;
-        count -= xfer;
-    }
+    printf("sideload-host file size %llu block size %lu\n", file_size, block_size);
 
-    if(count == 0) {
-        writex(s, "OKAY", 4);
-    } else {
-        writex(s, "FAIL", 4);
-    }
-    adb_close(fd);
-    adb_close(s);
+    int result = run_fuse(sfd, file_size, block_size);
 
-    if (count == 0) {
-        fprintf(stderr, "adbd exiting after successful sideload\n");
-        sleep(1);
-        exit(0);
-    }
+    printf("sideload_host finished\n");
+    sleep(1);
+    exit(result == 0 ? 0 : 1);
 }
 
-
 #if 0
 static void echo_service(int fd, void *cookie)
 {
@@ -149,7 +129,12 @@ int service_to_fd(const char *name)
     int ret = -1;
 
     if (!strncmp(name, "sideload:", 9)) {
-        ret = create_service_thread(sideload_service, (void*)(uintptr_t)atoi(name + 9));
+        // this exit status causes recovery to print a special error
+        // message saying to use a newer adb (that supports
+        // sideload-host).
+        exit(3);
+    } else if (!strncmp(name, "sideload-host:", 14)) {
+        ret = create_service_thread(sideload_host_service, (void*)(name + 14));
 #if 0
     } else if(!strncmp(name, "echo:", 5)){
         ret = create_service_thread(echo_service, 0);