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phonet: pep: fix use-after-free in pep_get_sb()

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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: 9641458d3e ("Phonet: Pipe End Point for Phonet Pipes protocol")
Cc: stable@vger.kernel.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260721-phonet_get_sb_uaf-v1-1-95fd7881cc4e@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Breno Leitao 2026-07-21 01:58:45 -07:00 committed by Jakub Kicinski
parent b9e558976b
commit 0f71f852a9
1 changed files with 2 additions and 0 deletions
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2
net/phonet/pep.c
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@ -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;