CVE-2026-53175

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

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

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

flushes every fragment queue that is not yet complete using

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

fragment queue but does not set INETFRAGCOMPLETE, and leaves

q->fragmentstail and q->lastrun_head pointing at the freed skbs.

The queue itself stays in the rhashtable.

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

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

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

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

it passes the INETFRAGCOMPLETE check and then dereferences the freed

fragmentstail. inetfragqueueinsert() reads FRAG_CB() and ->len of

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

slab use-after-free. IPv6, nfconntrackreasm6 and 6lowpan reassembly

share the same flush path and are affected as well.

Reset rbfragments, fragmentstail and lastrunhead in

inetfragqueue_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 fragmentstail. ipfrag_reinit() already

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

code there.