Vulnerability CVE-2024-26883
Published: 2024-04-17

Description:
In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix stackmap overflow check on 32-bit arches

The stackmap code relies on roundup_pow_of_two() to compute the number
of hash buckets, and contains an overflow check by checking if the
resulting value is 0. However, on 32-bit arches, the roundup code itself
can overflow by doing a 32-bit left-shift of an unsigned long value,
which is undefined behaviour, so it is not guaranteed to truncate
neatly. This was triggered by syzbot on the DEVMAP_HASH type, which
contains the same check, copied from the hashtab code.

The commit in the fixes tag actually attempted to fix this, but the fix
did not account for the UB, so the fix only works on CPUs where an
overflow does result in a neat truncation to zero, which is not
guaranteed. Checking the value before rounding does not have this
problem.

 References:
https://git.kernel.org/stable/c/d0e214acc59145ce25113f617311aa79dda39cb3
https://git.kernel.org/stable/c/21e5fa4688e1a4d3db6b72216231b24232f75c1d
https://git.kernel.org/stable/c/15641007df0f0d35fa28742b25c2a7db9dcd6895
https://git.kernel.org/stable/c/ca1f06e72dec41ae4f76e7b1a8a97265447b46ae
https://git.kernel.org/stable/c/f06899582ccee09bd85d0696290e3eaca9aa042d
https://git.kernel.org/stable/c/7070b274c7866a4c5036f8d54fcaf315c64ac33a
https://git.kernel.org/stable/c/43f798b9036491fb014b55dd61c4c5c3193267d0
https://git.kernel.org/stable/c/0971126c8164abe2004b8536b49690a0d6005b0a
https://git.kernel.org/stable/c/7a4b21250bf79eef26543d35bd390448646c536b
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