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macsec: fix replay protection at XPN lower-PN wrap

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In macsec_post_decrypt(), when pn is U32_MAX, pn + 1 overflows u32 to 0
and the first branch never fires. If next_pn_halves.lower is also in the
upper half, pn_same_half(pn, lower) is true and the XPN else-if does not
fire either, leaving next_pn_halves unchanged. An attacker that captures
the legitimate frame carrying pn == 0xFFFFFFFF on an XPN association
can then replay it indefinitely, since lowest_pn never rises above
the captured pn and macsec_decrypt() reconstructs the same IV.

Extend the XPN else-if to also fire when pn + 1 wraps to 0, so receipt
of pn == U32_MAX advances next_pn_halves to (upper + 1, 0).

Fixes: a21ecf0e03 ("macsec: Support XPN frame handling - IEEE 802.1AEbw")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Link: https://patch.msgid.link/SYBPR01MB78813FD49E58F253B989F197AF012@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Junrui Luo 2026-05-20 11:47:55 +08:00 committed by Jakub Kicinski
parent d47548a366
commit e68842b335
1 changed files with 2 additions and 1 deletions
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3
drivers/net/macsec.c
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@ -808,7 +808,8 @@ static bool macsec_post_decrypt(struct sk_buff *skb, struct macsec_secy *secy, u
if (pn + 1 > rx_sa->next_pn_halves.lower) {
rx_sa->next_pn_halves.lower = pn + 1;
} else if (secy->xpn &&
!pn_same_half(pn, rx_sa->next_pn_halves.lower)) {
(pn + 1 == 0 ||
!pn_same_half(pn, rx_sa->next_pn_halves.lower))) {
rx_sa->next_pn_halves.upper++;
rx_sa->next_pn_halves.lower = pn + 1;
}