Re: [PATCH net] net: tun: fix tun_napi_alloc_frags()

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Dec 12, 2024 at 10:22:47PM +0000, Eric Dumazet wrote:
> syzbot reported the following crash [1]
> 
> Issue came with the blamed commit. Instead of going through
> all the iov components, we keep using the first one
> and end up with a malformed skb.
> 
> [1]
> 
> kernel BUG at net/core/skbuff.c:2849 !
> Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
> CPU: 0 UID: 0 PID: 6230 Comm: syz-executor132 Not tainted 6.13.0-rc1-syzkaller-00407-g96b6fcc0ee41 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/25/2024
>  RIP: 0010:__pskb_pull_tail+0x1568/0x1570 net/core/skbuff.c:2848
> Code: 38 c1 0f 8c 32 f1 ff ff 4c 89 f7 e8 92 96 74 f8 e9 25 f1 ff ff e8 e8 ae 09 f8 48 8b 5c 24 08 e9 eb fb ff ff e8 d9 ae 09 f8 90 <0f> 0b 66 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90
> RSP: 0018:ffffc90004cbef30 EFLAGS: 00010293
> RAX: ffffffff8995c347 RBX: 00000000fffffff2 RCX: ffff88802cf45a00
> RDX: 0000000000000000 RSI: 00000000fffffff2 RDI: 0000000000000000
> RBP: ffff88807df0c06a R08: ffffffff8995b084 R09: 1ffff1100fbe185c
> R10: dffffc0000000000 R11: ffffed100fbe185d R12: ffff888076e85d50
> R13: ffff888076e85c80 R14: ffff888076e85cf4 R15: ffff888076e85c80
> FS:  00007f0dca6ea6c0(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f0dca6ead58 CR3: 00000000119da000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>   skb_cow_data+0x2da/0xcb0 net/core/skbuff.c:5284
>   tipc_aead_decrypt net/tipc/crypto.c:894 [inline]
>   tipc_crypto_rcv+0x402/0x24e0 net/tipc/crypto.c:1844
>   tipc_rcv+0x57e/0x12a0 net/tipc/node.c:2109
>   tipc_l2_rcv_msg+0x2bd/0x450 net/tipc/bearer.c:668
>   __netif_receive_skb_list_ptype net/core/dev.c:5720 [inline]
>   __netif_receive_skb_list_core+0x8b7/0x980 net/core/dev.c:5762
>   __netif_receive_skb_list net/core/dev.c:5814 [inline]
>   netif_receive_skb_list_internal+0xa51/0xe30 net/core/dev.c:5905
>   gro_normal_list include/net/gro.h:515 [inline]
>   napi_complete_done+0x2b5/0x870 net/core/dev.c:6256
>   napi_complete include/linux/netdevice.h:567 [inline]
>   tun_get_user+0x2ea0/0x4890 drivers/net/tun.c:1982
>   tun_chr_write_iter+0x10d/0x1f0 drivers/net/tun.c:2057
>  do_iter_readv_writev+0x600/0x880
>   vfs_writev+0x376/0xba0 fs/read_write.c:1050
>   do_writev+0x1b6/0x360 fs/read_write.c:1096
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Fixes: de4f5fed3f23 ("iov_iter: add iter_iovec() helper")
> Reported-by: syzbot+4f66250f6663c0c1d67e@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/675b61aa.050a0220.599f4.00bb.GAE@google.com/T/#u
> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Jens Axboe <axboe@kernel.dk>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/net/tun.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index d7a865ef370b6968c095510ae16b5196e30e54b9..e816aaba8e5f2ed06f8832f79553b6c976e75bb8 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1481,7 +1481,7 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile,
>  	skb->truesize += skb->data_len;
>  
>  	for (i = 1; i < it->nr_segs; i++) {
> -		const struct iovec *iov = iter_iov(it);
> +		const struct iovec *iov = iter_iov(it) + i;
>  		size_t fragsz = iov->iov_len;
>  		struct page *page;
>  		void *frag;
> -- 
> 2.47.1.613.gc27f4b7a9f-goog
>