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Miller" , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , netdev@vger.kernel.org, edumazet@kernel.org, Willem de Bruijn , Steffen Klassert , Tom Herbert , Cen Zhang , AutonomousCodeSecurity@microsoft.com, stable@vger.kernel.org, Taesoo Kim Subject: [PATCH net v2 2/2] net: gro: invalidate frag0 after a pull Date: Fri, 30 Oct 2026 13:59:55 +0100 Message-ID: <20261030125955.3107383-3-edumazet@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261030125955.3107383-1-edumazet@kernel.org> References: <20261030125955.3107383-1-edumazet@kernel.org> X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Since commit bd56a29c7a4e ("net: gro: change skb_gro_network_header()"), skb_gro_header_slow() no longer invalidates NAPI_GRO_CB(skb)->frag0 after pskb_may_pull(). skb_gro_may_pull() keeps comparing against the frag0_len value set in skb_gro_reset_offset(), assuming that after a slow pull, all later accesses are beyond frag0_len. This is not true: - udp4_gro_receive() and udp6_gro_receive() read the network header with skb_gro_network_header() after udp_gro_udphdr() pulled the UDP header. - vxlan_gro_receive() calls skb_gro_remcsum_cleanup() at a lower offset after the inner handlers pulled their headers. - skb_gro_remcsum_process() can pull beyond the inner Ethernet header before eth_gro_receive() reads it. - napi_frags_skb() calls __skb_pull(skb, ETH_HLEN) after a slow pull, so frag0 still points to the Ethernet header. If the pull consumed the first page fragment, __skb_pull_tail() released it. If the head had to grow, pskb_expand_head() freed the old one. These reads, and the 2-byte write in skb_gro_remcsum_cleanup(), then access memory the skb no longer holds a reference on. esp4_gro_receive(), esp6_gro_receive(), skb_gro_receive_list() and udp_gro_receive_segment() also pull directly and never invalidated frag0. Add skb_gro_frag0_invalidate(), which only clears frag0_len, and call it before each of these pulls. This is a single store in the slow path, and frag0 stays non NULL, so skb_gro_network_header() does not need a NULL test. frag0 must be invalidated even if the pull fails: __pskb_pull_tail() can return NULL after pskb_expand_head() freed the old head, for instance if a frag_list member has to be cloned or pulled. Fixes: bd56a29c7a4e ("net: gro: change skb_gro_network_header()") Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.") Cc: stable@vger.kernel.org Reported-by: Taesoo Kim Reported-by: Cen Zhang Tested-by: Cen Zhang Signed-off-by: Eric Dumazet --- include/net/gro.h | 10 ++++++++++ net/core/gro.c | 1 + net/ipv4/esp4_offload.c | 1 + net/ipv4/udp_offload.c | 1 + net/ipv6/esp6_offload.c | 1 + 5 files changed, 14 insertions(+) diff --git a/include/net/gro.h b/include/net/gro.h index 00b49b6b9e74..6f6affc8ab91 100644 --- a/include/net/gro.h +++ b/include/net/gro.h @@ -160,9 +160,19 @@ static inline bool skb_gro_may_pull(const struct sk_buff *skb, return likely(hlen <= NAPI_GRO_CB(skb)->frag0_len); } +/* A pull can release the page fragment frag0 points to, or reallocate + * skb->head, even if it fails. Call this before the pull, to make sure later + * skb_gro_header() and skb_gro_network_header() calls no longer use frag0. + */ +static inline void skb_gro_frag0_invalidate(struct sk_buff *skb) +{ + NAPI_GRO_CB(skb)->frag0_len = 0; +} + static inline void *skb_gro_header_slow(struct sk_buff *skb, unsigned int hlen, unsigned int offset) { + skb_gro_frag0_invalidate(skb); if (!pskb_may_pull(skb, hlen)) return NULL; diff --git a/net/core/gro.c b/net/core/gro.c index 1b033855a20d..bc88652e353a 100644 --- a/net/core/gro.c +++ b/net/core/gro.c @@ -238,6 +238,7 @@ int skb_gro_receive_list(struct sk_buff *p, struct sk_buff *skb) NAPI_GRO_CB(skb)->flush)) return -E2BIG; + skb_gro_frag0_invalidate(skb); if (!pskb_may_pull(skb, skb_gro_offset(skb))) { NAPI_GRO_CB(skb)->flush = 1; return -ENOMEM; diff --git a/net/ipv4/esp4_offload.c b/net/ipv4/esp4_offload.c index abd77162f5e7..2309468cfc3d 100644 --- a/net/ipv4/esp4_offload.c +++ b/net/ipv4/esp4_offload.c @@ -37,6 +37,7 @@ static struct sk_buff *esp4_gro_receive(struct list_head *head, __be32 seq; __be32 spi; + skb_gro_frag0_invalidate(skb); if (!pskb_pull(skb, offset)) return NULL; diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c index cf07c3c6611a..cd9d7426b227 100644 --- a/net/ipv4/udp_offload.c +++ b/net/ipv4/udp_offload.c @@ -743,6 +743,7 @@ static struct sk_buff *udp_gro_receive_segment(struct list_head *head, pp = p; } else { if (NAPI_GRO_CB(skb)->is_flist) { + skb_gro_frag0_invalidate(skb); if (!pskb_may_pull(skb, skb_gro_offset(skb))) { NAPI_GRO_CB(skb)->flush = 1; return NULL; diff --git a/net/ipv6/esp6_offload.c b/net/ipv6/esp6_offload.c index 22895521a57d..ca947cb94fb7 100644 --- a/net/ipv6/esp6_offload.c +++ b/net/ipv6/esp6_offload.c @@ -64,6 +64,7 @@ static struct sk_buff *esp6_gro_receive(struct list_head *head, if (NAPI_GRO_CB(skb)->proto == IPPROTO_UDP) encap_type = UDP_ENCAP_ESPINUDP; + skb_gro_frag0_invalidate(skb); if (!pskb_pull(skb, offset)) return NULL; -- 2.53.0