linux-kernel - Re: [PATCH 1/3] exec: Make do_coredump more resilient to recursive crashes (v9)

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Message-ID: <20090720162714.GA9060@hmsreliant.think-freely.org>
Date:	Mon, 20 Jul 2009 12:27:14 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, earl_chew@...lent.com,
	alan@...rguk.ukuu.org.uk, andi@...stfloor.org, oleg@...hat.com
Subject: Re: [PATCH 1/3] exec: Make do_coredump more resilient to recursive
	crashes (v9)

core_pattern: Change how we detect recursive dumps with core_pattern pipes

Change how we detect recursive dumps.  Currently we have a mechanism by which
we try to compare pathnames of the crashing process to the core_pattern path.
This is broken for a dozen reasons, and just doesn't work in any sort of robust
way.  I'm replacing it with the use of a 0 RLIMIT_CORE value.  Since helper
apps set RLIMIT_CORE to zero, we don't write out core files for any process with
that particular limit set.  It the core_pattern is a pipe, any non-zero limit is
translated to RLIM_INFINITY.  This allows complete dumps to be captured, but
prevents infinite recursion in the event that the core_pattern process itself
crashes.

Signed-off-by: Neil Horman <nhorman@...driver.com>
Reported-by: Earl Chew <earl_chew@...lent.com>


 exec.c |   43 +++++++++++++++++++++----------------------
 1 file changed, 21 insertions(+), 22 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 76ed4f6..21d2686 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1788,38 +1788,37 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
  	lock_kernel();
 	ispipe = format_corename(corename, 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) {
+		if (core_limit == 0) {
+			 /*
+			  * Normally core limits are irrelevant to pipes, since
+			  * we're not writing to the file system, but we use
+			  * core_limit of 0 here as a speacial value. Any
+			  * non-zero limit gets set to RLIM_INFINITY below, but
+			  * a limit of 0 skips the dump.  This is a consistent
+			  * way to catch recursive crashes.  We can still crash
+			  * if the core_pattern binary sets RLIM_CORE =  !0
+			  * but it runs as root, and can do lots of stupid things
+			  * Note that we use task_tgid_vnr here to grab the pid of the
+			  * process group leader.  That way we get the right pid if a thread
+			  * in a multi-threaded core_pattern process dies.
+			  */
+			printk(KERN_WARNING "Process %d(%s) has RLIMIT_CORE set to 0\n",
+			       task_tgid_vnr(current), current->comm);
+			printk(KERN_WARNING "Aborting core\n");
+			goto fail_unlock;
+		}
+ 
 		helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc);
 		if (!helper_argv) {
 			printk(KERN_WARNING "%s failed to allocate memory\n",
 			       __func__);
 			goto fail_unlock;
 		}
-		/* Terminate the string before the first option */
-		delimit = strchr(corename, ' ');
-		if (delimit)
-			*delimit = '\0';
-		delimit = strrchr(helper_argv[0], '/');
-		if (delimit)
-			delimit++;
-		else
-			delimit = helper_argv[0];
-		if (!strcmp(delimit, current->comm)) {
-			printk(KERN_NOTICE "Recursive core dump detected, "
-					"aborting\n");
-			goto fail_unlock;
-		}
 
 		core_limit = RLIM_INFINITY;
 
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