Bug 459471 - kernel: binfmt_misc.c: avoid potential kernel stack overflow [rhel-2.1]
kernel: binfmt_misc.c: avoid potential kernel stack overflow [rhel-2.1]
Product: Red Hat Enterprise Linux 2.1
Classification: Red Hat
Component: kernel (Show other bugs)
i386 Linux
medium Severity medium
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Assigned To: Don Howard
Martin Jenner
Depends On: 459462
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Reported: 2008-08-19 03:57 EDT by Eugene Teo (Security Response)
Modified: 2008-08-20 12:19 EDT (History)
2 users (show)

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Last Closed: 2008-08-20 12:19:02 EDT
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Description Eugene Teo (Security Response) 2008-08-19 03:57:47 EDT
+++ This bug was initially created as a clone of Bug #459462 +++

Description of problem:
Register the ":text:E::txt::/root/cat.txt:' rule in binfmt_misc (by root) and try launching the cat.txt file (by anyone) :) The result is - the endless recursion in the load_misc_binary -> open_exec -> load_misc_binary chain and stack overflow.

There's a similar problem with binfmt_script, and there's a sh_bang memner on linux_binprm structure to handle this, but simply raising this in binfmt_misc may break some setups when the interpreter of some misc binaries is a script.

So the proposal is to turn sh_bang into a bit, add a new one (the misc_bang) and raise it in load_misc_binary.  After this, even if we set up the misc -> script -> misc loop for binfmts one of them will step on its own bang and exit.

Note that this can be triggered with root help only.


--- Additional comment from eteo@redhat.com on 2008-08-19 03:17:02 EDT ---

Proposed upstream patch:

--- Additional comment from eteo@redhat.com on 2008-08-19 03:17:35 EDT ---

(In reply to comment #1)
> Proposed upstream patch:
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=3a2e7f47d71e1df86acc1dda6826890b6546a4e1

Note that there is a regression. See http://lkml.org/lkml/2008/8/18/544. The patch is not in upstream yet AFAIK.

--- Additional comment from eteo@redhat.com on 2008-08-19 03:46:16 EDT ---

Steps to Reproduce:
1. as root user, run echo ":text:E::txt::/cat.txt:" > /proc/sys/fs/binfmt_misc/register; touch /cat.txt; chmod +x /cat.txt
2) as normal user, run /cat.txt
Comment 2 Don Howard 2008-08-20 12:19:02 EDT
I can confirm that this reproducible on 2.1.

However, it doesn't rise to the level of critical bugfix, given that root-owned files must be mis-configured.

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