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tun: use pskb_may_pull_reason() and remove SKB_DROP_REASON_HDR_TRUNC

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tun_get_user() is the only user of SKB_DROP_REASON_HDR_TRUNC. It sets
it when pskb_may_pull() fails to pull the Ethernet header of a frame
written to a TAP device.

pskb_may_pull_reason() reports why the pull failed: PKT_TOO_SMALL if
the packet is shorter than requested, NOMEM if pulling the data into
the linear area fails. Use it for both header pulls in tun_get_user(),
on TAP and on TUN devices, and remove the now unused
SKB_DROP_REASON_HDR_TRUNC. The pull of the IP version byte on a TUN
device with IFF_NO_PI was reported as NOT_SPECIFIED and now reports
PKT_TOO_SMALL, for example when only the virtio-net header is written.

After a successful pull drop_reason is SKB_NOT_DROPPED_YET. The later
error paths without a reason of their own, the unknown IP version on
TUN, the virtio-net header conversion and the path that finds the
queue detached, relied on the SKB_DROP_REASON_NOT_SPECIFIED
initializer. Fall back to SKB_DROP_REASON_NOT_SPECIFIED at the free_skb
label, as vxlan_rcv() does, so that these paths, and any later one
without a reason of its own, keep reporting it.

The errors returned to user space do not change.

Suggested-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/netdev/20260923145931.GA2859441@shredder/
Assisted-by: LLM
Signed-off-by: Anton Danilov <littlesmilingcloud@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20261014054615.1656074-1-littlesmilingcloud@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Anton Danilov 2026-10-14 08:46:15 +03:00 committed by Paolo Abeni
parent f34e7e8875
commit 47b393b997
2 changed files with 5 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/net/tun.c
View File

@ -1903,7 +1903,8 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
if (tun->flags & IFF_NO_PI) {
u8 ip_version;
if (!pskb_may_pull(skb, 1)) {
drop_reason = pskb_may_pull_reason(skb, 1);
if (drop_reason) {
err = -EINVAL;
goto drop;
}
@ -1926,9 +1927,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
skb->protocol = pi.proto;
break;
case IFF_TAP:
if (!pskb_may_pull(skb, ETH_HLEN)) {
drop_reason = pskb_may_pull_reason(skb, ETH_HLEN);
if (drop_reason) {
err = -ENOMEM;
drop_reason = SKB_DROP_REASON_HDR_TRUNC;
goto drop;
}
skb_set_network_header(skb, ETH_HLEN);
@ -2065,6 +2066,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
dev_core_stats_rx_dropped_inc(tun->dev);
free_skb:
drop_reason = drop_reason ?: SKB_DROP_REASON_NOT_SPECIFIED;
if (!IS_ERR_OR_NULL(skb))
kfree_skb_reason(skb, drop_reason);

7
include/net/dropreason-core.h
View File

@ -82,7 +82,6 @@
FN(DEV_READY) \
FN(FULL_RING) \
FN(NOMEM) \
FN(HDR_TRUNC) \
FN(TAP_FILTER) \
FN(TAP_TXFILTER) \
FN(ICMP_CSUM) \
@ -427,12 +426,6 @@ enum skb_drop_reason {
SKB_DROP_REASON_FULL_RING,
/** @SKB_DROP_REASON_NOMEM: error due to OOM */
SKB_DROP_REASON_NOMEM,
/**
* @SKB_DROP_REASON_HDR_TRUNC: failed to trunc/extract the header from
* networking data, e.g., failed to pull the protocol header from
* frags via pskb_may_pull()
*/
SKB_DROP_REASON_HDR_TRUNC,
/**
* @SKB_DROP_REASON_TAP_FILTER: dropped by (ebpf) filter directly attached
* to tun/tap, e.g., via TUNSETFILTEREBPF