CVE-2026-74478um: vector: fix use-after-free in vector_mmsg_rx()

Official description

In the Linux kernel, the following vulnerability has been resolved: um: vector: fix use-after-free in vector_mmsg_rx() When vector_mmsg_rx() discards a packet whose overlay header fails verify_header(), it frees the skb and continues the loop: if (header_check < 0) { dev_kfree_skb_irq(skb); vp->estats.rx_encaps_errors++; continue; } The normal and short-packet paths fall through to the bottom of the loop body, which clears the consumed slot and advances the cursors: (*skbuff_vector) = NULL; mmsg_vector++; skbuff_vector++; The verify_header() < 0 path skips that via continue, so the freed skb is left in skbuff_vector[] and the cursors do not advance. The next iteration reads the same slot, gets the freed skb, and frees it again, producing a refcount underflow / use-after-free in the RX path. Discard the slot the same way the other paths do before continuing. Only transports whose verify_header() can return negative are affected: GRE and L2TPv3 do so on a cookie/session-id mismatch (raw/tap do not), so any peer on such a transport can trigger it without authentication.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/967c779c9853d2a1cc9cd8e61d300250c348f3d9
• https://git.kernel.org/stable/c/a7bc015bb798c525e7a82dd14225c6aeb994274b
• https://git.kernel.org/stable/c/7dc9781e320d664c9bdd50003c9acfddf363d1e1
• https://git.kernel.org/stable/c/4b9601595e8b6b5d18878cac0aeabc687d241111
• https://git.kernel.org/stable/c/67d58ab4f2ccf7145f3da07e025735a09c79de1b
• https://git.kernel.org/stable/c/180ff4c81faf01ec4e06082c9daa7c40518ead89
• https://git.kernel.org/stable/c/804b681002ead233abf49a3efd681f5468a835f9
• https://git.kernel.org/stable/c/af421e9aed3920c7ac88c24daa48606c7112feca