Re: [syzbot] [net?] KMSAN: uninit-value in validate_xmit_skb

[Eric Dumazet]

On Thu, Jan 11, 2024 at 9:27 PM syzbot
<syzbot+7f4d0ea3df4d4fa9a65f@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    fbafc3e621c3 Merge tag 'for_linus' of git://git.kernel.org..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1135ab95e80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e0c7078a6b901aa3
> dashboard link: https://syzkaller.appspot.com/bug?extid=7f4d0ea3df4d4fa9a65f
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15e15379e80000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=170f6981e80000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/1520f7b6daa4/disk-fbafc3e6.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/8b490af009d5/vmlinux-fbafc3e6.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/202ca200f4a4/bzImage-fbafc3e6.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+7f4d0ea3df4d4fa9a65f@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> =====================================================
> BUG: KMSAN: uninit-value in skb_gso_segment include/net/gso.h:83 [inline]
> BUG: KMSAN: uninit-value in validate_xmit_skb+0x10f2/0x1930 net/core/dev.c:3629
>  skb_gso_segment include/net/gso.h:83 [inline]
>  validate_xmit_skb+0x10f2/0x1930 net/core/dev.c:3629
>  __dev_queue_xmit+0x1eac/0x5130 net/core/dev.c:4341
>  dev_queue_xmit include/linux/netdevice.h:3134 [inline]
>  packet_xmit+0x9c/0x6b0 net/packet/af_packet.c:276
>  packet_snd net/packet/af_packet.c:3087 [inline]
>  packet_sendmsg+0x8b1d/0x9f30 net/packet/af_packet.c:3119
>  sock_sendmsg_nosec net/socket.c:730 [inline]
>  __sock_sendmsg net/socket.c:745 [inline]
>  ____sys_sendmsg+0x9c2/0xd60 net/socket.c:2584
>  ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
>  __sys_sendmsg net/socket.c:2667 [inline]
>  __do_sys_sendmsg net/socket.c:2676 [inline]
>  __se_sys_sendmsg net/socket.c:2674 [inline]
>  __x64_sys_sendmsg+0x307/0x490 net/socket.c:2674
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
>
> Uninit was created at:
>  slab_post_alloc_hook+0x129/0xa70 mm/slab.h:768
>  slab_alloc_node mm/slub.c:3478 [inline]
>  kmem_cache_alloc_node+0x5e9/0xb10 mm/slub.c:3523
>  kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:560
>  __alloc_skb+0x318/0x740 net/core/skbuff.c:651
>  alloc_skb include/linux/skbuff.h:1286 [inline]
>  alloc_skb_with_frags+0xc8/0xbd0 net/core/skbuff.c:6334
>  sock_alloc_send_pskb+0xa80/0xbf0 net/core/sock.c:2780
>  packet_alloc_skb net/packet/af_packet.c:2936 [inline]
>  packet_snd net/packet/af_packet.c:3030 [inline]
>  packet_sendmsg+0x70e8/0x9f30 net/packet/af_packet.c:3119
>  sock_sendmsg_nosec net/socket.c:730 [inline]
>  __sock_sendmsg net/socket.c:745 [inline]
>  ____sys_sendmsg+0x9c2/0xd60 net/socket.c:2584
>  ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2638
>  __sys_sendmsg net/socket.c:2667 [inline]
>  __do_sys_sendmsg net/socket.c:2676 [inline]
>  __se_sys_sendmsg net/socket.c:2674 [inline]
>  __x64_sys_sendmsg+0x307/0x490 net/socket.c:2674
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
>
> CPU: 0 PID: 5025 Comm: syz-executor279 Not tainted 6.7.0-rc7-syzkaller-00003-gfbafc3e621c3 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
> =====================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master

```
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 27cc1d4643219a44c01a2404124cd45ef46f7f3d..4dfa9b69ca8d95d43e44831bc166eadbe5715d3c
100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -3,6 +3,8 @@
 #define _LINUX_VIRTIO_NET_H

 #include <linux/if_vlan.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
 #include <linux/udp.h>
 #include <uapi/linux/tcp.h>
 #include <uapi/linux/virtio_net.h>
@@ -49,6 +51,7 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
                                        const struct virtio_net_hdr *hdr,
                                        bool little_endian)
 {
+       unsigned int nh_min_len = sizeof(struct iphdr);
        unsigned int gso_type = 0;
        unsigned int thlen = 0;
        unsigned int p_off = 0;
@@ -65,6 +68,7 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
                        gso_type = SKB_GSO_TCPV6;
                        ip_proto = IPPROTO_TCP;
                        thlen = sizeof(struct tcphdr);
+                       nh_min_len = sizeof(struct ipv6hdr);
                        break;
                case VIRTIO_NET_HDR_GSO_UDP:
                        gso_type = SKB_GSO_UDP;
@@ -100,7 +104,8 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
                if (!skb_partial_csum_set(skb, start, off))
                        return -EINVAL;

-               p_off = skb_transport_offset(skb) + thlen;
+               nh_min_len = max_t(u32, nh_min_len, skb_transport_offset(skb));
+               p_off = nh_min_len + thlen;
                if (!pskb_may_pull(skb, p_off))
                        return -EINVAL;
        } else {
@@ -140,7 +145,7 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,

                        skb_set_transport_header(skb, keys.control.thoff);
                } else if (gso_type) {
-                       p_off = thlen;
+                       p_off = nh_min_len + thlen;
                        if (!pskb_may_pull(skb, p_off))
                                return -EINVAL;
                }
```