core_pattern: ignore RLIMIT_CORE if core_pattern is a pipe

For some time /proc/sys/kernel/core_pattern has been able to set its output
destination as a pipe, allowing a user space helper to receive and
intellegently process a core.  This infrastructure however has some
shortcommings which can be enhanced.  Specifically:

1) The coredump code in the kernel should ignore RLIMIT_CORE limitation
   when core_pattern is a pipe, since file system resources are not being
   consumed in this case, unless the user application wishes to save the core,
   at which point the app is restricted by usual file system limits and
   restrictions.

2) The core_pattern code should be able to parse and pass options to the
   user space helper as an argv array.  The real core limit of the uid of the
   crashing proces should also be passable to the user space helper (since it
   is overridden to zero when called).

3) Some miscellaneous bugs need to be cleaned up (specifically the
   recognition of a recursive core dump, should the user mode helper itself
   crash.  Also, the core dump code in the kernel should not wait for the user
   mode helper to exit, since the same context is responsible for writing to
   the pipe, and a read of the pipe by the user mode helper will result in a
   deadlock.

This patch:

Remove the check of RLIMIT_CORE if core_pattern is a pipe.  In the event that
core_pattern is a pipe, the entire core will be fed to the user mode helper.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Cc: <martin.pitt@ubuntu.com>
Cc: <wwoods@redhat.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

6 files changed, 28 insertions, 23 deletions

diff --git a/fs/binfmt_aout.c b/fs/binfmt_aout.c
index 813a887..e176d19 100644
--- a/fs/binfmt_aout.c
+++ b/fs/binfmt_aout.c
@@ -31,7 +31,7 @@
 
 static int load_aout_binary(struct linux_binprm *, struct pt_regs * regs);
 static int load_aout_library(struct file*);
-static int aout_core_dump(long signr, struct pt_regs * regs, struct file *file);
+static int aout_core_dump(long signr, struct pt_regs *regs, struct file *file, unsigned long limit);
 
 static struct linux_binfmt aout_format = {
 	.module		= THIS_MODULE,
@@ -88,7 +88,7 @@ if (file->f_op->llseek) { \
  * dumping of the process results in another error..
  */
 
-static int aout_core_dump(long signr, struct pt_regs * regs, struct file *file)
+static int aout_core_dump(long signr, struct pt_regs *regs, struct file *file, unsigned long limit)
 {
 	mm_segment_t fs;
 	int has_dumped = 0;
@@ -123,23 +123,19 @@ static int aout_core_dump(long signr, struct pt_regs * regs, struct file *file)
 /* If the size of the dump file exceeds the rlimit, then see what would happen
    if we wrote the stack, but not the data area.  */
 #ifdef __sparc__
-	if ((dump.u_dsize+dump.u_ssize) >
-	    current->signal->rlim[RLIMIT_CORE].rlim_cur)
+	if ((dump.u_dsize + dump.u_ssize) > limit)
 		dump.u_dsize = 0;
 #else
-	if ((dump.u_dsize+dump.u_ssize+1) * PAGE_SIZE >
-	    current->signal->rlim[RLIMIT_CORE].rlim_cur)
+	if ((dump.u_dsize + dump.u_ssize+1) * PAGE_SIZE > limit)
 		dump.u_dsize = 0;
 #endif
 
 /* Make sure we have enough room to write the stack and data areas. */
 #ifdef __sparc__
-	if ((dump.u_ssize) >
-	    current->signal->rlim[RLIMIT_CORE].rlim_cur)
+	if (dump.u_ssize > limit)
 		dump.u_ssize = 0;
 #else
-	if ((dump.u_ssize+1) * PAGE_SIZE >
-	    current->signal->rlim[RLIMIT_CORE].rlim_cur)
+	if ((dump.u_ssize + 1) * PAGE_SIZE > limit)
 		dump.u_ssize = 0;
 #endif
 
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 2f31c4c..3dc6a12 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -52,7 +52,7 @@ static unsigned long elf_map (struct file *, unsigned long, struct elf_phdr *, i
  * don't even try.
  */
 #if defined(USE_ELF_CORE_DUMP) && defined(CONFIG_ELF_CORE)
-static int elf_core_dump(long signr, struct pt_regs *regs, struct file *file);
+static int elf_core_dump(long signr, struct pt_regs *regs, struct file *file, unsigned long limit);
 #else
 #define elf_core_dump	NULL
 #endif
@@ -1488,7 +1488,7 @@ static struct vm_area_struct *next_vma(struct vm_area_struct *this_vma,
  * and then they are actually written out.  If we run out of core limit
  * we just truncate.
  */
-static int elf_core_dump(long signr, struct pt_regs *regs, struct file *file)
+static int elf_core_dump(long signr, struct pt_regs *regs, struct file *file, unsigned long limit)
 {
 #define	NUM_NOTES	6
 	int has_dumped = 0;
@@ -1499,7 +1499,6 @@ static int elf_core_dump(long signr, struct pt_regs *regs, struct file *file)
 	struct vm_area_struct *vma, *gate_vma;
 	struct elfhdr *elf = NULL;
 	loff_t offset = 0, dataoff, foffset;
-	unsigned long limit = current->signal->rlim[RLIMIT_CORE].rlim_cur;
 	int numnote;
 	struct memelfnote *notes = NULL;
 	struct elf_prstatus *prstatus = NULL;	/* NT_PRSTATUS */
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index faae021..033861c 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -75,7 +75,7 @@ static int elf_fdpic_map_file_by_direct_mmap(struct elf_fdpic_params *,
 					     struct file *, struct mm_struct *);
 
 #if defined(USE_ELF_CORE_DUMP) && defined(CONFIG_ELF_CORE)
-static int elf_fdpic_core_dump(long, struct pt_regs *, struct file *);
+static int elf_fdpic_core_dump(long, struct pt_regs *, struct file *, unsigned long limit);
 #endif
 
 static struct linux_binfmt elf_fdpic_format = {
@@ -1552,7 +1552,7 @@ static int elf_fdpic_dump_segments(struct file *file, size_t *size,
  * we just truncate.
  */
 static int elf_fdpic_core_dump(long signr, struct pt_regs *regs,
-			       struct file *file)
+			       struct file *file, unsigned long limit)
 {
 #define	NUM_NOTES	6
 	int has_dumped = 0;
@@ -1563,7 +1563,6 @@ static int elf_fdpic_core_dump(long signr, struct pt_regs *regs,
 	struct vm_area_struct *vma;
 	struct elfhdr *elf = NULL;
 	loff_t offset = 0, dataoff;
-	unsigned long limit = current->signal->rlim[RLIMIT_CORE].rlim_cur;
 	int numnote;
 	struct memelfnote *notes = NULL;
 	struct elf_prstatus *prstatus = NULL;	/* NT_PRSTATUS */
diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
index fcb3405..265fac8 100644
--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -75,7 +75,7 @@ static int load_flat_shared_library(int id, struct lib_info *p);
 #endif
 
 static int load_flat_binary(struct linux_binprm *, struct pt_regs * regs);
-static int flat_core_dump(long signr, struct pt_regs * regs, struct file *file);
+static int flat_core_dump(long signr, struct pt_regs *regs, struct file *file, unsigned long limit);
 
 static struct linux_binfmt flat_format = {
 	.module		= THIS_MODULE,
@@ -90,7 +90,7 @@ static struct linux_binfmt flat_format = {
  * Currently only a stub-function.
  */
 
-static int flat_core_dump(long signr, struct pt_regs * regs, struct file *file)
+static int flat_core_dump(long signr, struct pt_regs *regs, struct file *file, unsigned long limit)
 {
 	printk("Process %s:%d received signr %d and should have core dumped\n",
 			current->comm, current->pid, (int) signr);
diff --git a/fs/binfmt_som.c b/fs/binfmt_som.c
index 5bcdaaf..9208c41 100644
--- a/fs/binfmt_som.c
+++ b/fs/binfmt_som.c
@@ -44,7 +44,7 @@ static int load_som_library(struct file *);
  * don't even try.
  */
 #if 0
-static int som_core_dump(long signr, struct pt_regs * regs);
+static int som_core_dump(long signr, struct pt_regs *regs, unsigned long limit);
 #else
 #define som_core_dump	NULL
 #endif
diff --git a/fs/exec.c b/fs/exec.c
index 550ae9b..86c4554 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1697,6 +1697,7 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
 	int fsuid = current->fsuid;
 	int flag = 0;
 	int ispipe = 0;
+	unsigned long core_limit = current->signal->rlim[RLIMIT_CORE].rlim_cur;
 
 	audit_core_dumps(signr);
 
@@ -1730,9 +1731,6 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
 	 */
 	clear_thread_flag(TIF_SIGPENDING);
 
-	if (current->signal->rlim[RLIMIT_CORE].rlim_cur < binfmt->min_coredump)
-		goto fail_unlock;
-
 	/*
 	 * lock_kernel() because format_corename() is controlled by sysctl, which
 	 * uses lock_kernel()
@@ -1740,7 +1738,20 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
  	lock_kernel();
 	ispipe = format_corename(corename, core_pattern, signr);
 	unlock_kernel();
+	/*
+	 * Don't bother to check the RLIMIT_CORE value if core_pattern points
+	 * to a pipe.  Since we're not writing directly to the filesystem
+	 * RLIMIT_CORE doesn't really apply, as no actual core file will be
+	 * created unless the pipe reader choses to write out the core file
+	 * at which point file size limits and permissions will be imposed
+	 * as it does with any other process
+	 */
+	if ((!ispipe) &&
+	   (core_limit < binfmt->min_coredump))
+		goto fail_unlock;
+
  	if (ispipe) {
+		core_limit = RLIM_INFINITY;
 		/* SIGPIPE can happen, but it's just never processed */
  		if(call_usermodehelper_pipe(corename+1, NULL, NULL, &file)) {
  			printk(KERN_INFO "Core dump to %s pipe failed\n",
@@ -1770,7 +1781,7 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
 	if (!ispipe && do_truncate(file->f_path.dentry, 0, 0, file) != 0)
 		goto close_fail;
 
-	retval = binfmt->core_dump(signr, regs, file);
+	retval = binfmt->core_dump(signr, regs, file, core_limit);
 
 	if (retval)
 		current->signal->group_exit_code |= 0x80;