6.12-stable review patch. If anyone has any objections, please let me know.
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From: Martin KaFai Lau martin.lau@kernel.org
[ Upstream commit d946f3c98328171fa50ddb908593cf833587f725 ]
The bpf_skb_check_mtu helper needs to use skb->transport_header when the BPF_MTU_CHK_SEGS flag is used:
bpf_skb_check_mtu(skb, ifindex, &mtu_len, 0, BPF_MTU_CHK_SEGS)
The transport_header is not always set. There is a WARN_ON_ONCE report when CONFIG_DEBUG_NET is enabled + skb->gso_size is set + bpf_prog_test_run is used:
WARNING: CPU: 1 PID: 2216 at ./include/linux/skbuff.h:3071 skb_gso_validate_network_len bpf_skb_check_mtu bpf_prog_3920e25740a41171_tc_chk_segs_flag # A test in the next patch bpf_test_run bpf_prog_test_run_skb
For a normal ingress skb (not test_run), skb_reset_transport_header is performed but there is plan to avoid setting it as described in commit 2170a1f09148 ("net: no longer reset transport_header in __netif_receive_skb_core()").
This patch fixes the bpf helper by checking skb_transport_header_was_set(). The check is done just before skb->transport_header is used, to avoid breaking the existing bpf prog. The WARN_ON_ONCE is limited to bpf_prog_test_run, so targeting bpf-next.
Fixes: 34b2021cc616 ("bpf: Add BPF-helper for MTU checking") Cc: Jesper Dangaard Brouer hawk@kernel.org Reported-by: Kaiyan Mei M202472210@hust.edu.cn Reported-by: Yinhao Hu dddddd@hust.edu.cn Signed-off-by: Martin KaFai Lau martin.lau@kernel.org Link: https://lore.kernel.org/r/20251112232331.1566074-1-martin.lau@linux.dev Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/filter.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c index 89ed625e14744..0d1f93f944f24 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -6353,9 +6353,12 @@ BPF_CALL_5(bpf_skb_check_mtu, struct sk_buff *, skb, */ if (skb_is_gso(skb)) { ret = BPF_MTU_CHK_RET_SUCCESS; - if (flags & BPF_MTU_CHK_SEGS && - !skb_gso_validate_network_len(skb, mtu)) - ret = BPF_MTU_CHK_RET_SEGS_TOOBIG; + if (flags & BPF_MTU_CHK_SEGS) { + if (!skb_transport_header_was_set(skb)) + return -EINVAL; + if (!skb_gso_validate_network_len(skb, mtu)) + ret = BPF_MTU_CHK_RET_SEGS_TOOBIG; + } } out: *mtu_len = mtu;