* [PATCH] net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() [not found] <CAHOBGNBvZOXGzzMDuHWw1RrRvbg4TZVH34jVDhc1nkHbW_URXA@mail.gmail.com> @ 2026-04-17 6:07 ` Zero Mark 2026-04-17 8:15 ` Willem de Bruijn 0 siblings, 1 reply; 6+ messages in thread From: Zero Mark @ 2026-04-17 6:07 UTC (permalink / raw) To: Willem de Bruijn Cc: security, David S . Miller, Jakub Kicinski, Eric Dumazet, netdev, Zero Mark 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 (gso_type, gso_size, flags, csum_start, csum_offset) between validation and use, bypassing all safety checks. This can lead to: - Out-of-bounds checksum writes via crafted csum_start/csum_offset - Malicious GSO segmentation parameters - Kernel memory corruption and potential local privilege escalation 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. Exploitation requires CAP_NET_RAW, which can be obtained without special privileges via user namespaces. Confirmed with a PoC on Linux 6.8.0 (Ubuntu): kprobe tracing on skb_partial_csum_set captured 77 race wins in 500,000 iterations. Affects all kernels since PACKET_VNET_HDR support was added to the TPACKET TX path (~v3.14). Fixes: 9ed988e5 ("packet: add vnet_hdr support for tpacket_snd") Signed-off-by: Zero Mark <patzilla007@gmail.com> --- net/packet/af_packet.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index abcdef012345..fedcba654321 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -2725,7 +2725,8 @@ static int tpacket_parse_header(struct packet_sock *po, void *frame, 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; @@ -2828,16 +2829,17 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) if (po->has_vnet_hdr) { - vnet_hdr = data; - data += sizeof(*vnet_hdr); - tp_len -= sizeof(*vnet_hdr); + memcpy(&vnet_hdr, data, sizeof(vnet_hdr)); + data += sizeof(vnet_hdr); + tp_len -= sizeof(vnet_hdr); if (tp_len < 0 || - __packet_snd_vnet_parse(vnet_hdr, tp_len)) { + __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, @@ -2875,11 +2877,11 @@ 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; -- 2.43.0 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() 2026-04-17 6:07 ` [PATCH] net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() Zero Mark @ 2026-04-17 8:15 ` Willem de Bruijn 2026-04-17 13:36 ` [PATCH net] " Zero Mark 0 siblings, 1 reply; 6+ messages in thread From: Willem de Bruijn @ 2026-04-17 8:15 UTC (permalink / raw) To: Zero Mark, Willem de Bruijn Cc: security, David S . Miller, Jakub Kicinski, Eric Dumazet, netdev, Zero Mark Zero Mark wrote: > 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 (gso_type, gso_size, > flags, csum_start, csum_offset) between validation and use, bypassing > all safety checks. > > This can lead to: > - Out-of-bounds checksum writes via crafted csum_start/csum_offset > - Malicious GSO segmentation parameters > - Kernel memory corruption and potential local privilege escalation > > 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. > > Exploitation requires CAP_NET_RAW, which can be obtained without > special privileges via user namespaces. > > Confirmed with a PoC on Linux 6.8.0 (Ubuntu): kprobe tracing on > skb_partial_csum_set captured 77 race wins in 500,000 iterations. No need to add such details on exploitability of bugs. > Affects all kernels since PACKET_VNET_HDR support was added to the > TPACKET TX path (~v3.14). > > Fixes: 9ed988e5 ("packet: add vnet_hdr support for tpacket_snd") This patch does not exist. Also 12-char SHA1. I think this should be Fixes: 1d036d25e560 ("packet: tpacket_snd gso and checksum offload") > Signed-off-by: Zero Mark <patzilla007@gmail.com> Thanks for the fix! Only it does not apply cleanly. Please mark fixes [PATCH net] and ensure that they apply to current netdev-net/main https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html > --- > net/packet/af_packet.c | 14 ++++++++------ > 1 file changed, 8 insertions(+), 6 deletions(-) > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > index abcdef012345..fedcba654321 100644 > --- a/net/packet/af_packet.c > +++ b/net/packet/af_packet.c > @@ -2725,7 +2725,8 @@ static int tpacket_parse_header(struct packet_sock *po, void *frame, > 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; > @@ -2828,16 +2829,17 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) > if (po->has_vnet_hdr) { > - vnet_hdr = data; > - data += sizeof(*vnet_hdr); > - tp_len -= sizeof(*vnet_hdr); > + memcpy(&vnet_hdr, data, sizeof(vnet_hdr)); Move the tp_len < 0 check before memcpy > + data += sizeof(vnet_hdr); > + tp_len -= sizeof(vnet_hdr); > if (tp_len < 0 || > - __packet_snd_vnet_parse(vnet_hdr, tp_len)) { > + __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, > @@ -2875,11 +2877,11 @@ 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; > -- > 2.43.0 > ^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH net] net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() 2026-04-17 8:15 ` Willem de Bruijn @ 2026-04-17 13:36 ` Zero Mark 2026-04-17 20:01 ` Willem de Bruijn 0 siblings, 1 reply; 6+ messages in thread From: Zero Mark @ 2026-04-17 13:36 UTC (permalink / raw) To: Willem de Bruijn Cc: security, David S . Miller, Jakub Kicinski, Eric Dumazet, netdev, Zero Mark 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: Zero Mark <patzilla007@gmail.com> --- net/packet/af_packet.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 4b043241fd56..8e6f3a734ba0 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -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 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) } } - 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; -- 2.53.0 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH net] net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() 2026-04-17 13:36 ` [PATCH net] " Zero Mark @ 2026-04-17 20:01 ` Willem de Bruijn 0 siblings, 0 replies; 6+ messages in thread From: Willem de Bruijn @ 2026-04-17 20:01 UTC (permalink / raw) To: Zero Mark, Willem de Bruijn Cc: security, David S . Miller, Jakub Kicinski, Eric Dumazet, netdev, Zero Mark Zero Mark wrote: > 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: Zero Mark <patzilla007@gmail.com> Reviewed-by: Willem de Bruijn <willemb@google.com> ^ permalink raw reply [flat|nested] 6+ messages in thread
[parent not found: <2026041858-estimator-shower-0f16@gregkh>]
* [PATCH net] net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() [not found] <2026041858-estimator-shower-0f16@gregkh> @ 2026-04-18 11:20 ` Bingquan Chen 2026-04-18 20:17 ` Willem de Bruijn 0 siblings, 1 reply; 6+ messages in thread From: Bingquan Chen @ 2026-04-18 11:20 UTC (permalink / raw) To: Willem de Bruijn, Greg KH Cc: Stephen Hemminger, security, David S . Miller, Jakub Kicinski, Eric Dumazet, netdev, Bingquan Chen 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 <patzilla007@gmail.com> --- net/packet/af_packet.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 4b043241fd56..8e6f3a734ba0 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -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 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) } } - 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; -- 2.53.0 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH net] net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() 2026-04-18 11:20 ` Bingquan Chen @ 2026-04-18 20:17 ` Willem de Bruijn 0 siblings, 0 replies; 6+ messages in thread From: Willem de Bruijn @ 2026-04-18 20:17 UTC (permalink / raw) To: Bingquan Chen, Willem de Bruijn, Greg KH Cc: Stephen Hemminger, security, David S . Miller, Jakub Kicinski, Eric Dumazet, netdev, Bingquan Chen Bingquan Chen wrote: > 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 <patzilla007@gmail.com> Reviewed-by: Willem de Bruijn <willemb@google.com> ^ permalink raw reply [flat|nested] 6+ messages in thread
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[not found] <CAHOBGNBvZOXGzzMDuHWw1RrRvbg4TZVH34jVDhc1nkHbW_URXA@mail.gmail.com>
2026-04-17 6:07 ` [PATCH] net/packet: fix TOCTOU race on mmap'd vnet_hdr in tpacket_snd() Zero Mark
2026-04-17 8:15 ` Willem de Bruijn
2026-04-17 13:36 ` [PATCH net] " Zero Mark
2026-04-17 20:01 ` Willem de Bruijn
[not found] <2026041858-estimator-shower-0f16@gregkh>
2026-04-18 11:20 ` Bingquan Chen
2026-04-18 20:17 ` Willem de Bruijn
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