5.4-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
[ Upstream commit d45cf1e7d7180256e17c9ce88e32e8061a7887fe ]
syzbot was able to craft a packet with very long IPv6 extension headers leading to an overflow of skb->transport_header.
This 16bit field has a limited range.
Add skb_reset_transport_header_careful() helper and use it from ipv6_gso_segment()
WARNING: CPU: 0 PID: 5871 at ./include/linux/skbuff.h:3032 skb_reset_transport_header include/linux/skbuff.h:3032 [inline] WARNING: CPU: 0 PID: 5871 at ./include/linux/skbuff.h:3032 ipv6_gso_segment+0x15e2/0x21e0 net/ipv6/ip6_offload.c:151 Modules linked in: CPU: 0 UID: 0 PID: 5871 Comm: syz-executor211 Not tainted 6.16.0-rc6-syzkaller-g7abc678e3084 #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:skb_reset_transport_header include/linux/skbuff.h:3032 [inline] RIP: 0010:ipv6_gso_segment+0x15e2/0x21e0 net/ipv6/ip6_offload.c:151 Call Trace: <TASK> skb_mac_gso_segment+0x31c/0x640 net/core/gso.c:53 nsh_gso_segment+0x54a/0xe10 net/nsh/nsh.c:110 skb_mac_gso_segment+0x31c/0x640 net/core/gso.c:53 __skb_gso_segment+0x342/0x510 net/core/gso.c:124 skb_gso_segment include/net/gso.h:83 [inline] validate_xmit_skb+0x857/0x11b0 net/core/dev.c:3950 validate_xmit_skb_list+0x84/0x120 net/core/dev.c:4000 sch_direct_xmit+0xd3/0x4b0 net/sched/sch_generic.c:329 __dev_xmit_skb net/core/dev.c:4102 [inline] __dev_queue_xmit+0x17b6/0x3a70 net/core/dev.c:4679
Fixes: d1da932ed4ec ("ipv6: Separate ipv6 offload support") Reported-by: syzbot+af43e647fd835acc02df@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/688a1a05.050a0220.5d226.0008.GAE@google.com/T... Signed-off-by: Eric Dumazet edumazet@google.com Reviewed-by: Dawid Osuchowski dawid.osuchowski@linux.intel.com Reviewed-by: Willem de Bruijn willemb@google.com Link: https://patch.msgid.link/20250730131738.3385939-1-edumazet@google.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/skbuff.h | 23 +++++++++++++++++++++++ net/ipv6/ip6_offload.c | 4 +++- 2 files changed, 26 insertions(+), 1 deletion(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 4edce28fb454..d9abd9e6833e 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2493,6 +2493,29 @@ static inline void skb_reset_transport_header(struct sk_buff *skb) skb->transport_header = skb->data - skb->head; }
+/** + * skb_reset_transport_header_careful - conditionally reset transport header + * @skb: buffer to alter + * + * Hardened version of skb_reset_transport_header(). + * + * Returns: true if the operation was a success. + */ +static inline bool __must_check +skb_reset_transport_header_careful(struct sk_buff *skb) +{ + long offset = skb->data - skb->head; + + if (unlikely(offset != (typeof(skb->transport_header))offset)) + return false; + + if (unlikely(offset == (typeof(skb->transport_header))~0U)) + return false; + + skb->transport_header = offset; + return true; +} + static inline void skb_set_transport_header(struct sk_buff *skb, const int offset) { diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c index b7b4ba68f3a2..0d9d11902b1b 100644 --- a/net/ipv6/ip6_offload.c +++ b/net/ipv6/ip6_offload.c @@ -109,7 +109,9 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
ops = rcu_dereference(inet6_offloads[proto]); if (likely(ops && ops->callbacks.gso_segment)) { - skb_reset_transport_header(skb); + if (!skb_reset_transport_header_careful(skb)) + goto out; + segs = ops->callbacks.gso_segment(skb, features); if (!segs) skb->network_header = skb_mac_header(skb) + nhoff - skb->head;