From 9a56796ad258786d3624eef5aefba394fc9bdded Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Thu, 15 Jan 2026 17:24:46 +0000 Subject: [PATCH 1/3] gue: Fix skb memleak with inner IP protocol 0. 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 Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260115172533.693652-2-kuniyu@google.com Signed-off-by: Jakub Kicinski --- 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); From 68578370f9b3a2aba5964b273312d51c581b6aad Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Thu, 15 Jan 2026 17:24:47 +0000 Subject: [PATCH 2/3] tools: ynl: Specify --no-line-number in ynl-regen.sh. 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 Signed-off-by: Kuniyuki Iwashima Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260115172533.693652-3-kuniyu@google.com Signed-off-by: Jakub Kicinski --- 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 From 7a9bc9e3f42391e4c187e099263cf7a1c4b69ff5 Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Thu, 15 Jan 2026 17:24:48 +0000 Subject: [PATCH 3/3] fou: Don't allow 0 for FOU_ATTR_IPPROTO. 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 Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260115172533.693652-4-kuniyu@google.com Signed-off-by: Jakub Kicinski --- 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, },