Red Hat Bugzilla – Bug 459471
kernel: binfmt_misc.c: avoid potential kernel stack overflow [rhel-2.1]
Last modified: 2008-08-20 12:19:02 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 email@example.com on 2008-08-19 03:17:02 EDT ---
Proposed upstream patch:
--- Additional comment from firstname.lastname@example.org on 2008-08-19 03:17:35 EDT ---
(In reply to comment #1)
> Proposed upstream patch:
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 email@example.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
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.