CVE-2026-53175

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

inet: frags: fix use-after-free caused by the fqdir_pre_exit() flush

On netns teardown, fqdir_pre_exit() walks the fqdir rhashtable and

flushes every fragment queue that is not yet complete using

inet_frag_queue_flush(). That helper frees all the skbs queued on the

fragment queue but does not set INET_FRAG_COMPLETE, and leaves

q->fragments_tail and q->last_run_head pointing at the freed skbs.

The queue itself stays in the rhashtable.

fqdir_pre_exit() first lowers high_thresh to 0 to stop new queue lookups,

but it cannot stop a fragment that already obtained the queue through

inet_frag_find() earlier and stalled just before taking the queue lock.

Once that fragment resumes after the flush and takes the queue lock,

it passes the INET_FRAG_COMPLETE check and then dereferences the freed

fragments_tail. inet_frag_queue_insert() reads FRAG_CB() and ->len of

that pointer and, on the append path, writes ->next_frag, causing a

slab use-after-free. IPv6, nf_conntrack_reasm6 and 6lowpan reassembly

share the same flush path and are affected as well.

Reset rb_fragments, fragments_tail and last_run_head in

inet_frag_queue_flush() so a flushed queue no longer points at the

freed skbs. A fragment that resumes after the flush and takes the

queue lock then finds an empty queue and starts a new run instead of

dereferencing the freed fragments_tail. ip_frag_reinit() already

performed this reset after its own flush, so drop the now duplicate

code there.