CVE-2023-53728

/// Technical description

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

posix-timers: Ensure timer ID search-loop limit is valid

posix_timer_add() tries to allocate a posix timer ID by starting from the

cached ID which was stored by the last successful allocation.

This is done in a loop searching the ID space for a free slot one by

one. The loop has to terminate when the search wrapped around to the

starting point.

But that's racy vs. establishing the starting point. That is read out

lockless, which leads to the following problem:

CPU0 CPU1

posix_timer_add()

start = sig->posix_timer_id;

lock(hash_lock);

... posix_timer_add()

if (++sig->posix_timer_id < 0)

start = sig->posix_timer_id;

sig->posix_timer_id = 0;

So CPU1 can observe a negative start value, i.e. -1, and the loop break

never happens because the condition can never be true:

if (sig->posix_timer_id == start)

break;

While this is unlikely to ever turn into an

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References