CVE-2023-53698

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

xsk: fix refcount underflow in error path

Fix a refcount underflow problem reported by syzbot that can happen when a system is running out of memory. If xp_alloc_tx_descs() fails, and it can only fail due to not having enough memory, then the error path is triggered. In this error path, the refcount of the pool is decremented as it has incremented before. However, the reference to the pool in the socket was not nulled. This means that when the socket is closed later, the socket teardown logic will think that there is a pool attached to the socket and try to decrease the refcount again, leading to a refcount underflow.

I chose this fix as it involved adding just a single line. Another option would have been to move xp_get_pool() and the assignment of xs->pool to after the if-statement and using xs_umem->pool instead of xs->pool in the whole if-statement resulting in somewhat simpler code, but this would have led to much more churn in the code base perhaps making it harder to backport.

In xsk_bind(), if xp_alloc_tx_descs() fails (OOM), the error path decremented the pool’s refcount via xp_put_pool(xs->pool) but did not null out xs->pool. On socket teardown, the code would attempt another put, causing a refcount underflow and potential kernel BUG or use-after-free. The fix sets xs->pool = NULL after the first put, preventing the double decrement. Practical triggering typically requires privileged ability to create/bind AF_XDP sockets and induce low-memory conditions.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.