[PATCH v2 net 0/3] fou/gue: Fix skb memleak with inner protocol 0.

[PATCH v2 net 0/3] fou/gue: Fix skb memleak with inner protocol 0.

[Kuniyuki Iwashima]

syzbot reported memleak for a GUE packet with its inner
protocol number 0.

Patch 1 fixes the issue, and patch 3 fixes the same issue
in FOU.


Changes:
  v2:
    * Add patch 2 for ynl-regen.sh (Jakub)
    * Patch 3
      * Updated ynl spec and regenerated fou_nl.c (Jakub)

  v1: https://lore.kernel.org/netdev/20260112200736.1884171-1-kuniyu@google.com/


Kuniyuki Iwashima (3):
  gue: Fix skb memleak with inner IP protocol 0.
  tools: ynl: Specify --no-line-number in ynl-regen.sh.
  fou: Don't allow 0 for FOU_ATTR_IPPROTO.

 Documentation/netlink/specs/fou.yaml | 2 ++
 net/ipv4/fou_core.c                  | 3 +++
 net/ipv4/fou_nl.c                    | 2 +-
 tools/net/ynl/ynl-regen.sh           | 2 +-
 4 files changed, 7 insertions(+), 2 deletions(-)

-- 
2.52.0.457.g6b5491de43-goog

[PATCH v2 net 1/3] gue: Fix skb memleak with inner IP protocol 0.

[Kuniyuki Iwashima]

syzbot reported skb memleak below. [0]

The repro generated a GUE packet with its inner protocol 0.

gue_udp_recv() returns -guehdr->proto_ctype for "resubmit"
in ip_protocol_deliver_rcu(), but this only works with
non-zero protocol number.

Let's drop such packets.

Note that 0 is a valid number (IPv6 Hop-by-Hop Option).

I think it is not practical to encap HOPOPT in GUE, so once
someone starts to complain, we could pass down a resubmit
flag pointer to distinguish two zeros from the upper layer:

  * no error
  * resubmit HOPOPT

[0]
BUG: memory leak
unreferenced object 0xffff888109695a00 (size 240):
  comm "syz.0.17", pid 6088, jiffies 4294943096
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............
  backtrace (crc a84b336f):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270
    __build_skb+0x23/0x60 net/core/skbuff.c:474
    build_skb+0x20/0x190 net/core/skbuff.c:490
    __tun_build_skb drivers/net/tun.c:1541 [inline]
    tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636
    tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770
    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999
    new_sync_write fs/read_write.c:593 [inline]
    vfs_write+0x45d/0x710 fs/read_write.c:686
    ksys_write+0xa7/0x170 fs/read_write.c:738
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: 37dd0247797b1 ("gue: Receive side for Generic UDP Encapsulation")
Reported-by: syzbot+4d8c7d16b0e95c0d0f0d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6965534b.050a0220.38aacd.0001.GAE@google.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/fou_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/fou_core.c b/net/ipv4/fou_core.c
index 3970b6b7ace5..ab8f309f8925 100644
--- a/net/ipv4/fou_core.c
+++ b/net/ipv4/fou_core.c
@@ -215,6 +215,9 @@ static int gue_udp_recv(struct sock *sk, struct sk_buff *skb)
 		return gue_control_message(skb, guehdr);
 
 	proto_ctype = guehdr->proto_ctype;
+	if (unlikely(!proto_ctype))
+		goto drop;
+
 	__skb_pull(skb, sizeof(struct udphdr) + hdrlen);
 	skb_reset_transport_header(skb);
 
-- 
2.52.0.457.g6b5491de43-goog

[PATCH v2 net 2/3] tools: ynl: Specify --no-line-number in ynl-regen.sh.

[Kuniyuki Iwashima]

If grep.lineNumber is enabled in .gitconfig,

  [grep]
  lineNumber = true

ynl-regen.sh fails with the following error:

  $ ./tools/net/ynl/ynl-regen.sh -f
  ...
  ynl_gen_c.py: error: argument --mode: invalid choice: '4:' (choose from user, kernel, uapi)
  	GEN 4:	net/ipv4/fou_nl.c

Let's specify --no-line-number explicitly.

Fixes: be5bea1cc0bf ("net: add basic C code generators for Netlink")
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 tools/net/ynl/ynl-regen.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/net/ynl/ynl-regen.sh b/tools/net/ynl/ynl-regen.sh
index 81b4ecd89100..d9809276db98 100755
--- a/tools/net/ynl/ynl-regen.sh
+++ b/tools/net/ynl/ynl-regen.sh
@@ -21,7 +21,7 @@ files=$(git grep --files-with-matches '^/\* YNL-GEN \(kernel\|uapi\|user\)')
 for f in $files; do
     # params:     0       1      2     3
     #         $YAML YNL-GEN kernel $mode
-    params=( $(git grep -B1 -h '/\* YNL-GEN' $f | sed 's@/\*\(.*\)\*/@\1@') )
+    params=( $(git grep --no-line-number -B1 -h '/\* YNL-GEN' $f | sed 's@/\*\(.*\)\*/@\1@') )
     args=$(sed -n 's@/\* YNL-ARG \(.*\) \*/@\1@p' $f)
 
     if [ $f -nt ${params[0]} -a -z "$force" ]; then
-- 
2.52.0.457.g6b5491de43-goog

Re: [PATCH v2 net 2/3] tools: ynl: Specify --no-line-number in ynl-regen.sh.

[Eric Dumazet]

On Thu, Jan 15, 2026 at 6:25 PM Kuniyuki Iwashima <kuniyu@google.com> wrote:
>
> If grep.lineNumber is enabled in .gitconfig,
>
>   [grep]
>   lineNumber = true
>
> ynl-regen.sh fails with the following error:
>
>   $ ./tools/net/ynl/ynl-regen.sh -f
>   ...
>   ynl_gen_c.py: error: argument --mode: invalid choice: '4:' (choose from user, kernel, uapi)
>         GEN 4:  net/ipv4/fou_nl.c
>
> Let's specify --no-line-number explicitly.

Reviewed-by: Eric Dumazet <edumazet@google.com>

[PATCH v2 net 3/3] fou: Don't allow 0 for FOU_ATTR_IPPROTO.

[Kuniyuki Iwashima]

fou_udp_recv() has the same problem mentioned in the previous
patch.

If FOU_ATTR_IPPROTO is set to 0, skb is not freed by
fou_udp_recv() nor "resubmit"-ted in ip_protocol_deliver_rcu().

Let's forbid 0 for FOU_ATTR_IPPROTO.

Fixes: 23461551c0062 ("fou: Support for foo-over-udp RX path")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
v2:
  * Updated ynl spec and generated fou_nl.c (Jakub)
---
 Documentation/netlink/specs/fou.yaml | 2 ++
 net/ipv4/fou_nl.c                    | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/netlink/specs/fou.yaml b/Documentation/netlink/specs/fou.yaml
index 8e7974ec453f..331f1b342b3a 100644
--- a/Documentation/netlink/specs/fou.yaml
+++ b/Documentation/netlink/specs/fou.yaml
@@ -39,6 +39,8 @@ attribute-sets:
       -
         name: ipproto
         type: u8
+        checks:
+          min: 1
       -
         name: type
         type: u8
diff --git a/net/ipv4/fou_nl.c b/net/ipv4/fou_nl.c
index 7a99639204b1..309d5ba983d0 100644
--- a/net/ipv4/fou_nl.c
+++ b/net/ipv4/fou_nl.c
@@ -15,7 +15,7 @@
 const struct nla_policy fou_nl_policy[FOU_ATTR_IFINDEX + 1] = {
 	[FOU_ATTR_PORT] = { .type = NLA_BE16, },
 	[FOU_ATTR_AF] = { .type = NLA_U8, },
-	[FOU_ATTR_IPPROTO] = { .type = NLA_U8, },
+	[FOU_ATTR_IPPROTO] = NLA_POLICY_MIN(NLA_U8, 1),
 	[FOU_ATTR_TYPE] = { .type = NLA_U8, },
 	[FOU_ATTR_REMCSUM_NOPARTIAL] = { .type = NLA_FLAG, },
 	[FOU_ATTR_LOCAL_V4] = { .type = NLA_U32, },
-- 
2.52.0.457.g6b5491de43-goog

Re: [PATCH v2 net 3/3] fou: Don't allow 0 for FOU_ATTR_IPPROTO.

[Eric Dumazet]

On Thu, Jan 15, 2026 at 6:25 PM Kuniyuki Iwashima <kuniyu@google.com> wrote:
>
> fou_udp_recv() has the same problem mentioned in the previous
> patch.
>
> If FOU_ATTR_IPPROTO is set to 0, skb is not freed by
> fou_udp_recv() nor "resubmit"-ted in ip_protocol_deliver_rcu().
>
> Let's forbid 0 for FOU_ATTR_IPPROTO.
>
> Fixes: 23461551c0062 ("fou: Support for foo-over-udp RX path")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
> ---

Reviewed-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH v2 net 0/3] fou/gue: Fix skb memleak with inner protocol 0.

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 15 Jan 2026 17:24:45 +0000 you wrote:
> syzbot reported memleak for a GUE packet with its inner
> protocol number 0.
> 
> Patch 1 fixes the issue, and patch 3 fixes the same issue
> in FOU.
> 
> 
> [...]

Here is the summary with links:
  - [v2,net,1/3] gue: Fix skb memleak with inner IP protocol 0.
    https://git.kernel.org/netdev/net/c/9a56796ad258
  - [v2,net,2/3] tools: ynl: Specify --no-line-number in ynl-regen.sh.
    https://git.kernel.org/netdev/net/c/68578370f9b3
  - [v2,net,3/3] fou: Don't allow 0 for FOU_ATTR_IPPROTO.
    https://git.kernel.org/netdev/net/c/7a9bc9e3f423

You are awesome, thank you!
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