[PATCH 42/88] exec: use -ELOOP for max recursion depth

[Ben Hutchings]

On Thu, 2013-03-14 at 10:35 +0000, Luis Henriques wrote:
> 3.5.7.8 -stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Kees Cook <keescook at chromium.org>
> 
> commit d740269867021faf4ce38a449353d2b986c34a67 upstream.
> 
> To avoid an explosion of request_module calls on a chain of abusive
> scripts, fail maximum recursion with -ELOOP instead of -ENOEXEC. As soon
> as maximum recursion depth is hit, the error will fail all the way back
> up the chain, aborting immediately.
> 
> This also has the side-effect of stopping the user's shell from attempting
> to reexecute the top-level file as a shell script. As seen in the
> dash source:
> 
>         if (cmd != path_bshell && errno == ENOEXEC) {
>                 *argv-- = cmd;
>                 *argv = cmd = path_bshell;
>                 goto repeat;
>         }
> 
> The above logic was designed for running scripts automatically that lacked
> the "#!" header, not to re-try failed recursion. On a legitimate -ENOEXEC,
> things continue to behave as the shell expects.
> 
> Additionally, when tracking recursion, the binfmt handlers should not be
> involved. The recursion being tracked is the depth of calls through
> search_binary_handler(), so that function should be exclusively responsible
> for tracking the depth.
> 
> Signed-off-by: Kees Cook <keescook at chromium.org>
> Cc: halfdog <me at halfdog.net>
> Cc: P J P <ppandit at redhat.com>
> Cc: Alexander Viro <viro at zeniv.linux.org.uk>
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> [ luis: backport to 3.5 ]
> Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
[...]

Greg, I also included this in 3.2.y (commit 511d07b) but it is missing
from 3.0.y and 3.4.y.  I hope one or other of these backports will be
suitable for them (it was just a context fix for 3.2.y).

Ben.

-- 
Ben Hutchings
When you say `I wrote a program that crashed Windows', people just stare ...
and say `Hey, I got those with the system, *for free*'. - Linus Torvalds
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