FAILED: patch "[PATCH] net/packet: fix TOCTOU race on mmap'd vnet_hdr in" failed to apply to 5.15-stable tree

PATCH New [email protected] 2 participants 2 messages Apr 24 – Apr 25

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[email protected]

author maintainer

2026-04-24 09:50 UTC #0 lore raw

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 2c054e17d9d41f1020376806c7f750834ced4dc5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026042433-handpick-copy-d2e1@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2c054e17d9d41f1020376806c7f750834ced4dc5 Mon Sep 17 00:00:00 2001
From: Bingquan Chen <[email protected]>
Date: Sat, 18 Apr 2026 19:20:06 +0800
Subject: [PATCH] net/packet: fix TOCTOU race on mmap'd vnet_hdr in
tpacket_snd()

In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points directly into the mmap'd TX ring buffer shared with userspace. The kernel validates the header via __packet_snd_vnet_parse() but then re-reads all fields later in virtio_net_hdr_to_skb(). A concurrent userspace thread can modify the vnet_hdr fields between validation and use, bypassing all safety checks.

The non-TPACKET path (packet_snd()) already correctly copies vnet_hdr to a stack-local variable. All other vnet_hdr consumers in the kernel (tun.c, tap.c, virtio_net.c) also use stack copies. The TPACKET TX path is the only caller of virtio_net_hdr_to_skb() that reads directly from user-controlled shared memory.

Fix this by copying vnet_hdr from the mmap'd ring buffer to a stack-local variable before validation and use, consistent with the approach used in packet_snd() and all other callers.

Fixes 1d036d25e560 ("packet: tpacket_snd gso and checksum offload")

Signed-off-by Bingquan Chen <[email protected]>

Reviewed-by Willem de Bruijn <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

net/packet/af_packet.c +13 -8

index 4b043241fd56..8e6f3a734ba0 100644
@@ -2718,7 +2718,8 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 {
 	struct sk_buff *skb = NULL;
 	struct net_device *dev;
-	struct virtio_net_hdr *vnet_hdr = NULL;
+	struct virtio_net_hdr vnet_hdr;
+	bool has_vnet_hdr = false;
 	struct sockcm_cookie sockc;
 	__be16 proto;
 	int err, reserve = 0;

@@ -2819,16 +2820,20 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 		hlen = LL_RESERVED_SPACE(dev);
 		tlen = dev->needed_tailroom;
 		if (vnet_hdr_sz) {
-			vnet_hdr = data;
 			data += vnet_hdr_sz;
 			tp_len -= vnet_hdr_sz;
-			if (tp_len < 0 ||
-			    __packet_snd_vnet_parse(vnet_hdr, tp_len)) {
+			if (tp_len < 0) {
+				tp_len = -EINVAL;
+				goto tpacket_error;
+			}
+			memcpy(&vnet_hdr, data - vnet_hdr_sz, sizeof(vnet_hdr));
+			if (__packet_snd_vnet_parse(&vnet_hdr, tp_len)) {
 				tp_len = -EINVAL;
 				goto tpacket_error;
 			}
 			copylen = __virtio16_to_cpu(vio_le(),
-						    vnet_hdr->hdr_len);
+						    vnet_hdr.hdr_len);
+			has_vnet_hdr = true;
 		}
 		copylen = max_t(int, copylen, dev->hard_header_len);
 		skb = sock_alloc_send_skb(&po->sk,

@@ -2865,12 +2870,12 @@ tpacket_error:
 			}
 		}
 
-		if (vnet_hdr_sz) {
-			if (virtio_net_hdr_to_skb(skb, vnet_hdr, vio_le())) {
+		if (has_vnet_hdr) {
+			if (virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le())) {
 				tp_len = -EINVAL;
 				goto tpacket_error;
 			}
-			virtio_net_hdr_set_proto(skb, vnet_hdr);
+			virtio_net_hdr_set_proto(skb, &vnet_hdr);
 		}
 
 		skb->destructor = tpacket_destruct_skb;

Sasha Levin

maintainer

2026-04-25 10:01 UTC #1 lore raw

PATCH 1/1 net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd()

From: Bingquan Chen <[email protected]>

[ Upstream commit 2c054e17d9d41f1020376806c7f750834ced4dc5 ]

Fix this by copying vnet_hdr from the mmap'd ring buffer to a stack-local variable before validation and use, consistent with the approach used in packet_snd() and all other callers.

Fixes 1d036d25e560 ("packet: tpacket_snd gso and checksum offload")

Signed-off-by Bingquan Chen <[email protected]>

Reviewed-by Willem de Bruijn <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Jakub Kicinski <[email protected]>

[ replaced `vnet_hdr_sz` with `sizeof(vnet_hdr)` and `if (vnet_hdr_sz)` with `if (po->has_vnet_hdr)` ]

Signed-off-by Sasha Levin <[email protected]>

---
 net/packet/af_packet.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

net/packet/af_packet.c +15 ~~-10~~

index d1ad069271f8b..e0ea02e86b38e 100644
@@ -2729,7 +2729,8 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 {
 	struct sk_buff *skb = NULL;
 	struct net_device *dev;
-	struct virtio_net_hdr *vnet_hdr = NULL;
+	struct virtio_net_hdr vnet_hdr;
+	bool has_vnet_hdr = false;
 	struct sockcm_cookie sockc;
 	__be16 proto;
 	int err, reserve = 0;

@@ -2829,16 +2830,20 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 		hlen = LL_RESERVED_SPACE(dev);
 		tlen = dev->needed_tailroom;
 		if (po->has_vnet_hdr) {
-			vnet_hdr = data;
-			data += sizeof(*vnet_hdr);
-			tp_len -= sizeof(*vnet_hdr);
-			if (tp_len < 0 ||
-			    __packet_snd_vnet_parse(vnet_hdr, tp_len)) {
+			data += sizeof(vnet_hdr);
+			tp_len -= sizeof(vnet_hdr);
+			if (tp_len < 0) {
+				tp_len = -EINVAL;
+				goto tpacket_error;
+			}
+			memcpy(&vnet_hdr, data - sizeof(vnet_hdr), sizeof(vnet_hdr));
+			if (__packet_snd_vnet_parse(&vnet_hdr, tp_len)) {
 				tp_len = -EINVAL;
 				goto tpacket_error;
 			}
 			copylen = __virtio16_to_cpu(vio_le(),
-						    vnet_hdr->hdr_len);
+						    vnet_hdr.hdr_len);
+			has_vnet_hdr = true;
 		}
 		copylen = max_t(int, copylen, dev->hard_header_len);
 		skb = sock_alloc_send_skb(&po->sk,

@@ -2875,12 +2880,12 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 			}
 		}
 
-		if (po->has_vnet_hdr) {
-			if (virtio_net_hdr_to_skb(skb, vnet_hdr, vio_le())) {
+		if (has_vnet_hdr) {
+			if (virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le())) {
 				tp_len = -EINVAL;
 				goto tpacket_error;
 			}
-			virtio_net_hdr_set_proto(skb, vnet_hdr);
+			virtio_net_hdr_set_proto(skb, &vnet_hdr);
 		}
 
 		skb->destructor = tpacket_destruct_skb;

Signature · 1 line

2.53.0