From: Michael Bommarito Date: Mon, 22 Jun 2026 12:47:22 +0000 (-0400) Subject: um: vector: fix use-after-free in vector_mmsg_rx() X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=af421e9aed3920c7ac88c24daa48606c7112feca;p=thirdparty%2Flinux.git 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. Fixes: 49da7e64f33e ("High Performance UML Vector Network Driver") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Michael Bommarito Signed-off-by: Richard Weinberger --- diff --git a/arch/um/drivers/vector_kern.c b/arch/um/drivers/vector_kern.c index 2cc90055499a..8a70b3a62553 100644 --- a/arch/um/drivers/vector_kern.c +++ b/arch/um/drivers/vector_kern.c @@ -995,6 +995,9 @@ static int vector_mmsg_rx(struct vector_private *vp, int budget) */ dev_kfree_skb_irq(skb); vp->estats.rx_encaps_errors++; + (*skbuff_vector) = NULL; + mmsg_vector++; + skbuff_vector++; continue; } if (header_check > 0) {