pep_get_sb() doesn't consider that pskb_may_pull() might have relocated the skb data, and continue to access the older pointer, causing UAF. Reproduced under KASAN: BUG: KASAN: slab-use-after-free in pep_get_sb+0x234/0x3b0 Read of size 1 at addr ff11000105510f50 by task repro/157 pep_get_sb+0x234/0x3b0 pipe_handler_do_rcv+0x5f7/0xa10 pep_do_rcv+0x203/0x410 __sk_receive_skb+0x471/0x4a0 phonet_rcv+0x5b3/0x6c0 __netif_receive_skb+0xcc/0x1d0 Refetch the header with skb_header_pointer() after pskb_may_pull(), so the possibly stale pointer is no longer dereferenced. There are better ways to solve this, but, this is the less instrusive one. Fixes: 9641458d3ec4 ("Phonet: Pipe End Point for Phonet Pipes protocol") Cc: stable@vger.kernel.org Signed-off-by: Breno Leitao --- This showed up in sashiko report, when I've sent my other patchset https://lore.kernel.org/all/20260720-getsockopt_phase4-v2-0-8a08fcfa0d72@debian.org/ --- net/phonet/pep.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/phonet/pep.c b/net/phonet/pep.c index 7069271393933..31b29e3ca7bc6 100644 --- a/net/phonet/pep.c +++ b/net/phonet/pep.c @@ -55,6 +55,8 @@ static unsigned char *pep_get_sb(struct sk_buff *skb, u8 *ptype, u8 *plen, ph = skb_header_pointer(skb, 0, 2, &h); if (ph == NULL || ph->sb_len < 2 || !pskb_may_pull(skb, ph->sb_len)) return NULL; + /* pskb_may_pull() may have reallocated the head; refetch ph. */ + ph = skb_header_pointer(skb, 0, 2, &h); ph->sb_len -= 2; *ptype = ph->sb_type; *plen = ph->sb_len; --- base-commit: 1c975de3343cdef506f2eecc833cc1f14b0401c4 change-id: 20260720-phonet_get_sb_uaf-8745e9d9d62c Best regards, -- Breno Leitao