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

block, bfq: fix uaf for accessing waker_bfqq after splitting

After commit 42c306ed7233 ("block, bfq: don't break merge chain in
bfq_split_bfqq()"), if the current procress is the last holder of bfqq,
the bfqq can be freed after bfq_split_bfqq(). Hence recored the bfqq and
then access bfqq->waker_bfqq may trigger UAF. What's more, the waker_bfqq
may in the merge chain of bfqq, hence just recored waker_bfqq is still
not safe.

Fix the problem by adding a helper bfq_waker_bfqq() to check if
bfqq->waker_bfqq is in the merge chain, and current procress is the only
holder.

kernel.org https://git.kernel.org/stable/c/0780451f03bf518bc032a7c584de8f92e2d39d7f [No types assigned]

kernel.org https://git.kernel.org/stable/c/0b8bda0ff17156cd3f60944527c9d8c9f99f1583 [No types assigned]

kernel.org https://git.kernel.org/stable/c/1ba0403ac6447f2d63914fb760c44a3b19c44eaf [No types assigned]

kernel.org https://git.kernel.org/stable/c/63a07379fdb6c72450cb05294461c6016b8b7726 [No types assigned]

kernel.org https://git.kernel.org/stable/c/cae58d19121a70329cf971359e2518c93fec04fe [No types assigned]

kernel.org https://git.kernel.org/stable/c/de0456460f2abf921e356ed2bd8da87a376680bd [No types assigned]