Re: [PATCH v2] sanitize task->comm to avoid leaking escape codes

From: KOSAKI Motohiro
Date: Thu Jun 24 2010 - 19:56:37 EST

> Through get_task_comm() and many direct uses of task->comm in the kernel,
> it is possible for escape codes and other non-printables to leak into
> dmesg, syslog, etc. In the worst case, these strings could be used to
> attack administrators using vulnerable terminal emulators, and at least
> cause confusion through the injection of \r characters.
> This patch sanitizes task->comm to only contain printable characters
> when it is set. Additionally, it redefines get_task_comm so that it is
> more obvious when misused by callers (presently nothing was incorrectly
> calling get_task_comm's unsafe use of strncpy).
> Signed-off-by: Kees Cook <kees.cook@xxxxxxxxxxxxx>

I've reviewed this patch briefly, Here is my personal concern...

On Linux, non-printable leaking is fundamental, only fixing task->comm
doesn't solve syslog exploit issue. Probably all /proc/kmsg user should
have escaping non-pritables code.

However, task->comm is one of most easy injection data of kernel, because
we have prctl(PR_SET_NAME), attacker don't need root privilege. So,
conservative assumption seems guard from crappy fault. Plus, this patch
is very small and our small TASK_COMM_LEN lead that we don't need
big performance concern.

So, I don't find demerit in this proposal. but I'm not security specialist,
it's only personal thinking.

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