From: Petr Wozniak Date: Sun, 21 Jun 2026 10:03:27 +0000 (+0200) Subject: xfrm: fix stale skb->prev after async crypto steals a GSO segment X-Git-Tag: v7.2-rc4~17^2~14^2~8 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3f4c3919baf0944ad96580467c302bc6c7758b00;p=thirdparty%2Fkernel%2Flinux.git xfrm: fix stale skb->prev after async crypto steals a GSO segment skb_gso_segment() leaves the segment list head with ->prev pointing at the last segment, an invariant validate_xmit_skb_list() relies on when it sets its tail pointer (tail = skb->prev). When validate_xmit_xfrm() walks a GSO list and some segments are stolen by async crypto (->xmit() returns -EINPROGRESS), those segments are unlinked from the list but the head ->prev is never updated. If the last segment is the one stolen, the returned head still has ->prev pointing at it, even though it is now owned by the crypto engine and may be freed. validate_xmit_skb_list() later does tail->next = skb, writing through that stale pointer -- a use-after-free. Repoint skb->prev at the last retained segment before returning. Fixes: f53c723902d1 ("net: Add asynchronous callbacks for xfrm on layer 2.") Signed-off-by: Petr Wozniak Signed-off-by: Steffen Klassert --- diff --git a/net/xfrm/xfrm_device.c b/net/xfrm/xfrm_device.c index 19c77f09acc9..aec1e1184a71 100644 --- a/net/xfrm/xfrm_device.c +++ b/net/xfrm/xfrm_device.c @@ -224,6 +224,14 @@ struct sk_buff *validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t featur pskb = skb2; } + /* skb_gso_segment() set skb->prev to the last segment, but async + * crypto may have stolen it above without updating ->prev. Repoint + * it at the last retained segment so validate_xmit_skb_list() does + * not chain onto a segment now owned by the crypto engine. + */ + if (skb) + skb->prev = pskb; + return skb ? skb : ERR_PTR(-EINPROGRESS); } EXPORT_SYMBOL_GPL(validate_xmit_xfrm);