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net: icmp: avoid invalid transport header access in icmp_send tracepoint

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syzbot reported a WARNING triggered by DEBUG_NET_WARN_ON_ONCE():

 WARNING: at skb_transport_header include/linux/skbuff.h:3087 [inline]
 WARNING: at udp_hdr include/linux/udp.h:23 [inline]
 WARNING: at do_trace_event_raw_event_icmp_send include/trace/events/icmp.h:30 [inline]
 WARNING: at trace_event_raw_event_icmp_send+0x48c/0x6ec include/trace/events/icmp.h:11
 Call trace:
  skb_transport_header include/linux/skbuff.h:3087 [inline]
  udp_hdr include/linux/udp.h:23 [inline]
  do_trace_event_raw_event_icmp_send include/trace/events/icmp.h:30 [inline]
  trace_event_raw_event_icmp_send+0x48c/0x6ec include/trace/events/icmp.h:11
  __traceiter_icmp_send include/trace/events/icmp.h:11 [inline]
  __do_trace_icmp_send include/trace/events/icmp.h:11 [inline]
  trace_icmp_send+0x320/0x49c include/trace/events/icmp.h:11
  __icmp_send+0xcfc/0x11d8 net/ipv4/icmp.c:1013
  ipv4_send_dest_unreach net/ipv4/route.c:1280 [inline]
  ipv4_link_failure+0x57c/0x8dc net/ipv4/route.c:1287
  dst_link_failure include/net/dst.h:438 [inline]
  vti_tunnel_xmit+0xe40/0x17a4 net/ipv4/ip_vti.c:307

TP_fast_assign() unconditionally calls udp_hdr(skb) before checking
whether the packet is UDP. Furthermore, __icmp_send() can be invoked
from paths (e.g., link failures, ARP errors, forwarding, AF_PACKET)
where skb->transport_header was never initialized (~0U).

Under CONFIG_DEBUG_NET=y, calling skb_transport_header(skb) triggers
DEBUG_NET_WARN_ON_ONCE(!skb_transport_header_was_set(skb)).

Fix this by:
1. Only parsing transport info when iph->protocol == IPPROTO_UDP.
2. Using skb_header_pointer() at skb_network_offset(skb) + (iph->ihl << 2)
   to safely fetch the UDP header without assuming transport_header is set.

Fixes: db3efdcf70 ("net/ipv4: add tracepoint for icmp_send")
Reported-by: syzbot+6d2762674103618994b0@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a8d5538.91706f20.ef82.0009.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Peilin He <he.peilin@zte.com.cn>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20260825084551.1562967-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2026-08-25 08:45:51 +00:00 committed by Jakub Kicinski
parent dddf197f29
commit 7fcc2fe39f
1 changed files with 8 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
include/trace/events/icmp.h
View File

@ -27,17 +27,20 @@ TRACE_EVENT(icmp_send,
TP_fast_assign(
struct iphdr *iph = ip_hdr(skb);
struct udphdr *uh = udp_hdr(skb);
int proto_4 = iph->protocol;
struct udphdr _uh, *uh = NULL;
__be32 *p32;
__entry->skbaddr = skb;
__entry->type = type;
__entry->code = code;
if (proto_4 != IPPROTO_UDP || (u8 *)uh < skb->head ||
(u8 *)uh + sizeof(struct udphdr)
> skb_tail_pointer(skb)) {
if (iph->protocol == IPPROTO_UDP)
uh = skb_header_pointer(skb,
skb_network_offset(skb) +
(iph->ihl << 2),
sizeof(_uh), &_uh);
if (!uh) {
__entry->sport = 0;
__entry->dport = 0;
__entry->ulen = 0;