Re: [PATCH ipsec v2 2/7] xfrm: esp4: use the current sequence number for the IV

[sashiko-bot@kernel.org]

> When a GSO packet is split in software for IPv4 ESP,
> validate_xmit_xfrm() calls esp_xmit() for each segment. These
> segments have XFRM_GSO_SEGMENT set, but after the split, skb_is_gso()
> returns false for each skb, so each call increments xo->seq.low by one
> after writing the ESP sequence number.
> 
> The low bits are saved in seq before the increment, but esp.seqno is
> set afterwards, using the saved low bits and the high bits from
> xo->seq.hi.
> 
> When encryption is done in software with ESN enabled, the segment at
> (H, 0xffffffff) uses (H+1, 0xffffffff) to generate the AES-GCM IV
> because xo->seq.hi has already been incremented when the low bits
> wrapped. One full 32-bit cycle later, if the packet at
> (H+1, 0xffffffff) on the same SA is non-GSO, it generates the same IV.
> 
> Move the assignment to esp.seqno before xo->seq is advanced. This
> saves H before the wrap increments xo->seq.hi to H+1, so the segment
> at (H, 0xffffffff) generates its IV from (H, 0xffffffff).
> 
> Fixes: 4b549ccce941 ("xfrm: replay: Fix ESN wrap around for GSO")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jérémy Jean <Jeremy.Jean@oss.cyber.gouv.fr>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261108142652.1330952-1-Jeremy.Jean@oss.cyber.gouv.fr?part=2