Handling argc==0 in the kernel [LWN.net]

Handling argc==0 in the kernel

Posted Jan 28, 2022 20:24 UTC (Fri) by khim (subscriber, #9252)
In reply to: Handling argc==0 in the kernel by dskoll
Parent article: Handling argc==0 in the kernel

Nope. It couldn't. Since that one, too, may be /proc/self/exe (and, indeed there are one case where pattern exec("/proc/self/exe", NULL, NULL); is used).

So it's not bullet-proof and, I think, few examples where this Linux-only misfeature is exploited are not worth inventing crazy schemes.

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Handling argc==0 in the kernel

Posted Jan 28, 2022 21:07 UTC (Fri) by dskoll (subscriber, #1630) [Link] (3 responses)

But if execve("/proc/self/exe", NULL, NULL); succeeds, under what circumstances could /proc/self/exe not be relied on in the execed program?

Handling argc==0 in the kernel

Posted Jan 28, 2022 21:15 UTC (Fri) by khim (subscriber, #9252) [Link] (2 responses)

When someone would call `realpath` on it? That never happened in real-world usecase so yeah, you are right, that may a way out.

Of course this would also break most tests anyway thus it's not clear if couple of real programs are worth that complexity.

Kernel config option looks more and more sensible: we know such programs are rare, but how rare exactly?

Handling argc==0 in the kernel

Posted Jan 28, 2022 21:26 UTC (Fri) by dskoll (subscriber, #1630) [Link] (1 responses)

realpath is an executable; I think you meant readlink(2). But my point is this: If the original execve call succeeds, then "/proc/self/exe" must still be valid in the exec'd program. if /proc/self/exe were not valid, then the execve call would fail.

Handling argc==0 in the kernel

Posted Jan 29, 2022 2:48 UTC (Sat) by comex (subscriber, #71521) [Link]

Not to get lost in the weeds, but realpath is also the name of a function; see `man 3 realpath`.