Description
In the Linux kernel, the following vulnerability has been resolved:
net: always dissect GSO packets in __virtio_net_hdr_to_skb()
Commit 9e8db5913264 ("net: avoid false positives in untrusted gso
validation") added a '&& skb->network_header' check before flow-dissecting
GSO packets without VIRTIO_NET_HDR_F_NEEDS_CSUM in
__virtio_net_hdr_to_skb(), because some callers (such as tun_get_user(),
tun_xdp_one(), virtnet_receive_done(), and raw_verify_header()) called
virtio_net_hdr_*_to_skb() before initializing skb->network_header and
skb->dev.
Because __alloc_skb() and __build_skb_around() zero-initialize
skb->network_header to 0 (unlike mac_header and transport_header which
are initialized to ~0U), those four callers always had
skb->network_header == 0 and bypassed flow dissection in
__virtio_net_hdr_to_skb(). More generally, skb->network_header is an
offset from skb->head (where 0 is also a valid offset whenever
skb_headroom(skb) is 0), not a boolean flag.
Whenever the 'if (gso_type && skb->network_header)' branch was skipped,
the fallback 'else if (gso_type)' only pulled nh_min_len + thlen (40 bytes
for TCPv4) without dissecting the packet, without validating ip_proto or
n_proto, and without setting skb->transport_header.
If the packet has a malformed network header, it is not rejected and a
subsequent skb_probe_transport_header() also fails, leaving
skb->transport_header at ~0U (0xffff). Similarly, if an IPv4 packet
carries IP options (ihl > 5) or an IPv6 packet carries extension headers,
pulling only nh_min_len + thlen can leave the TCP header outside
skb->head. In both cases, tcp_hdrlen(skb) in skb_gso_transport_seglen()
reads out-of-bounds:
BUG: KASAN: slab-out-of-bounds in skb_gso_transport_seglen
Read of size 2 by task poc/133
skb_gso_transport_seglen (net/core/gso.c:155)
skb_gso_validate_mac_len (net/core/gso.c:270)
tbf_enqueue (net/sched/sch_tbf.c:260)
dev_qdisc_enqueue (net/core/dev.c:4227)
__dev_queue_xmit (net/core/dev.c:4884)
In addition, checking virtio_net_hdr_match_proto() only inside
'if (!skb->protocol)' before flow dissection both skipped validation when
skb->protocol was pre-set by the caller and rejected VLAN-tagged frames
whose outer L2 protocol is ETH_P_8021Q or ETH_P_8021AD.
Fix this by:
1. Initializing skb->dev and skb->network_header (plus skb->protocol for
IFF_TUN) before virtio_net_hdr_*_to_skb() in tun_get_user(),
tun_xdp_one(), virtnet_receive_done(), and raw_verify_header(). In
tun_get_user(), drop the redundant skb_reset_mac_header(skb) in the
IFF_TUN case since __virtio_net_hdr_to_skb() unconditionally resets
mac_header.
2. Removing '&& skb->network_header' and the unvalidated
'else if (gso_type)' fallback in __virtio_net_hdr_to_skb() so all GSO
packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are flow-dissected, have
their transport header pulled into linear data, and have
skb->transport_header set.
3. Moving the virtio_net_hdr_match_proto() check to after
skb_flow_dissect_flow_keys_basic(), validating keys.basic.n_proto
against hdr_gso_type.
net: always dissect GSO packets in __virtio_net_hdr_to_skb()
Commit 9e8db5913264 ("net: avoid false positives in untrusted gso
validation") added a '&& skb->network_header' check before flow-dissecting
GSO packets without VIRTIO_NET_HDR_F_NEEDS_CSUM in
__virtio_net_hdr_to_skb(), because some callers (such as tun_get_user(),
tun_xdp_one(), virtnet_receive_done(), and raw_verify_header()) called
virtio_net_hdr_*_to_skb() before initializing skb->network_header and
skb->dev.
Because __alloc_skb() and __build_skb_around() zero-initialize
skb->network_header to 0 (unlike mac_header and transport_header which
are initialized to ~0U), those four callers always had
skb->network_header == 0 and bypassed flow dissection in
__virtio_net_hdr_to_skb(). More generally, skb->network_header is an
offset from skb->head (where 0 is also a valid offset whenever
skb_headroom(skb) is 0), not a boolean flag.
Whenever the 'if (gso_type && skb->network_header)' branch was skipped,
the fallback 'else if (gso_type)' only pulled nh_min_len + thlen (40 bytes
for TCPv4) without dissecting the packet, without validating ip_proto or
n_proto, and without setting skb->transport_header.
If the packet has a malformed network header, it is not rejected and a
subsequent skb_probe_transport_header() also fails, leaving
skb->transport_header at ~0U (0xffff). Similarly, if an IPv4 packet
carries IP options (ihl > 5) or an IPv6 packet carries extension headers,
pulling only nh_min_len + thlen can leave the TCP header outside
skb->head. In both cases, tcp_hdrlen(skb) in skb_gso_transport_seglen()
reads out-of-bounds:
BUG: KASAN: slab-out-of-bounds in skb_gso_transport_seglen
Read of size 2 by task poc/133
skb_gso_transport_seglen (net/core/gso.c:155)
skb_gso_validate_mac_len (net/core/gso.c:270)
tbf_enqueue (net/sched/sch_tbf.c:260)
dev_qdisc_enqueue (net/core/dev.c:4227)
__dev_queue_xmit (net/core/dev.c:4884)
In addition, checking virtio_net_hdr_match_proto() only inside
'if (!skb->protocol)' before flow dissection both skipped validation when
skb->protocol was pre-set by the caller and rejected VLAN-tagged frames
whose outer L2 protocol is ETH_P_8021Q or ETH_P_8021AD.
Fix this by:
1. Initializing skb->dev and skb->network_header (plus skb->protocol for
IFF_TUN) before virtio_net_hdr_*_to_skb() in tun_get_user(),
tun_xdp_one(), virtnet_receive_done(), and raw_verify_header(). In
tun_get_user(), drop the redundant skb_reset_mac_header(skb) in the
IFF_TUN case since __virtio_net_hdr_to_skb() unconditionally resets
mac_header.
2. Removing '&& skb->network_header' and the unvalidated
'else if (gso_type)' fallback in __virtio_net_hdr_to_skb() so all GSO
packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are flow-dissected, have
their transport header pulled into linear data, and have
skb->transport_header set.
3. Moving the virtio_net_hdr_match_proto() check to after
skb_flow_dissect_flow_keys_basic(), validating keys.basic.n_proto
against hdr_gso_type.
Published:
2026-10-23
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
No analysis available yet.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
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| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No remediation available yet.
Tracking
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Advisories
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References
History
Fri, 23 Oct 2026 12:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: net: always dissect GSO packets in __virtio_net_hdr_to_skb() Commit 9e8db5913264 ("net: avoid false positives in untrusted gso validation") added a '&& skb->network_header' check before flow-dissecting GSO packets without VIRTIO_NET_HDR_F_NEEDS_CSUM in __virtio_net_hdr_to_skb(), because some callers (such as tun_get_user(), tun_xdp_one(), virtnet_receive_done(), and raw_verify_header()) called virtio_net_hdr_*_to_skb() before initializing skb->network_header and skb->dev. Because __alloc_skb() and __build_skb_around() zero-initialize skb->network_header to 0 (unlike mac_header and transport_header which are initialized to ~0U), those four callers always had skb->network_header == 0 and bypassed flow dissection in __virtio_net_hdr_to_skb(). More generally, skb->network_header is an offset from skb->head (where 0 is also a valid offset whenever skb_headroom(skb) is 0), not a boolean flag. Whenever the 'if (gso_type && skb->network_header)' branch was skipped, the fallback 'else if (gso_type)' only pulled nh_min_len + thlen (40 bytes for TCPv4) without dissecting the packet, without validating ip_proto or n_proto, and without setting skb->transport_header. If the packet has a malformed network header, it is not rejected and a subsequent skb_probe_transport_header() also fails, leaving skb->transport_header at ~0U (0xffff). Similarly, if an IPv4 packet carries IP options (ihl > 5) or an IPv6 packet carries extension headers, pulling only nh_min_len + thlen can leave the TCP header outside skb->head. In both cases, tcp_hdrlen(skb) in skb_gso_transport_seglen() reads out-of-bounds: BUG: KASAN: slab-out-of-bounds in skb_gso_transport_seglen Read of size 2 by task poc/133 skb_gso_transport_seglen (net/core/gso.c:155) skb_gso_validate_mac_len (net/core/gso.c:270) tbf_enqueue (net/sched/sch_tbf.c:260) dev_qdisc_enqueue (net/core/dev.c:4227) __dev_queue_xmit (net/core/dev.c:4884) In addition, checking virtio_net_hdr_match_proto() only inside 'if (!skb->protocol)' before flow dissection both skipped validation when skb->protocol was pre-set by the caller and rejected VLAN-tagged frames whose outer L2 protocol is ETH_P_8021Q or ETH_P_8021AD. Fix this by: 1. Initializing skb->dev and skb->network_header (plus skb->protocol for IFF_TUN) before virtio_net_hdr_*_to_skb() in tun_get_user(), tun_xdp_one(), virtnet_receive_done(), and raw_verify_header(). In tun_get_user(), drop the redundant skb_reset_mac_header(skb) in the IFF_TUN case since __virtio_net_hdr_to_skb() unconditionally resets mac_header. 2. Removing '&& skb->network_header' and the unvalidated 'else if (gso_type)' fallback in __virtio_net_hdr_to_skb() so all GSO packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are flow-dissected, have their transport header pulled into linear data, and have skb->transport_header set. 3. Moving the virtio_net_hdr_match_proto() check to after skb_flow_dissect_flow_keys_basic(), validating keys.basic.n_proto against hdr_gso_type. | |
| Title | net: always dissect GSO packets in __virtio_net_hdr_to_skb() | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-23T12:19:13.873Z
Reserved: 2026-09-25T10:25:14.382Z
Link: CVE-2026-98954
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.