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binfmt_misc.c: avoid potential kernel stack overflow

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This can be triggered with root help only, but...

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.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Pavel Emelyanov 2008-04-29 00:59:24 -07:00 • committed by Linus Torvalds
parent cbd9b67bd3
commit 3a2e7f47d7
4 changed files with 10 additions and 3 deletions
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6
fs/binfmt_misc.c
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@ -115,6 +115,12 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
if (!enabled)
goto _ret;
retval = -ENOEXEC;
if (bprm->misc_bang)
goto _ret;
bprm->misc_bang = 1;
/* to keep locking time low, we copy the interpreter string */
read_lock(&entries_lock);
fmt = check_file(bprm);