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Date:   Thu, 14 May 2020 17:20:00 -0400
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Arjun Roy <arjunroy@...gle.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] tcp: fix error recovery in tcp_zerocopy_receive()

On Thu, May 14, 2020 at 4:58 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> If user provides wrong virtual address in TCP_ZEROCOPY_RECEIVE
> operation we want to return -EINVAL error.
>
> But depending on zc->recv_skip_hint content, we might return
> -EIO error if the socket has SOCK_DONE set.
>
> Make sure to return -EINVAL in this case.
>
> BUG: KMSAN: uninit-value in tcp_zerocopy_receive net/ipv4/tcp.c:1833 [inline]
> BUG: KMSAN: uninit-value in do_tcp_getsockopt+0x4494/0x6320 net/ipv4/tcp.c:3685
> CPU: 1 PID: 625 Comm: syz-executor.0 Not tainted 5.7.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1c9/0x220 lib/dump_stack.c:118
>  kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
>  __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
>  tcp_zerocopy_receive net/ipv4/tcp.c:1833 [inline]
>  do_tcp_getsockopt+0x4494/0x6320 net/ipv4/tcp.c:3685
>  tcp_getsockopt+0xf8/0x1f0 net/ipv4/tcp.c:3728
>  sock_common_getsockopt+0x13f/0x180 net/core/sock.c:3131
>  __sys_getsockopt+0x533/0x7b0 net/socket.c:2177
>  __do_sys_getsockopt net/socket.c:2192 [inline]
>  __se_sys_getsockopt+0xe1/0x100 net/socket.c:2189
>  __x64_sys_getsockopt+0x62/0x80 net/socket.c:2189
>  do_syscall_64+0xb8/0x160 arch/x86/entry/common.c:297
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x45c829
> Code: 0d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f1deeb72c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
> RAX: ffffffffffffffda RBX: 00000000004e01e0 RCX: 000000000045c829
> RDX: 0000000000000023 RSI: 0000000000000006 RDI: 0000000000000009
> RBP: 000000000078bf00 R08: 0000000020000200 R09: 0000000000000000
> R10: 00000000200001c0 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000000001d8 R14: 00000000004d3038 R15: 00007f1deeb736d4
>
> Local variable ----zc@...tcp_getsockopt created at:
>  do_tcp_getsockopt+0x1a74/0x6320 net/ipv4/tcp.c:3670
>  do_tcp_getsockopt+0x1a74/0x6320 net/ipv4/tcp.c:3670
>
> Fixes: 05255b823a61 ("tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>

Thanks for the fix!

> ---
>  net/ipv4/tcp.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index a385fcaaa03beed9bfeabdebc12371e34e0649de..dd401757eea1f0187b0e547828f794e62eb895b8 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1764,10 +1764,11 @@ static int tcp_zerocopy_receive(struct sock *sk,
>
>         down_read(&current->mm->mmap_sem);
>
> -       ret = -EINVAL;
>         vma = find_vma(current->mm, address);
> -       if (!vma || vma->vm_start > address || vma->vm_ops != &tcp_vm_ops)
> -               goto out;
> +       if (!vma || vma->vm_start > address || vma->vm_ops != &tcp_vm_ops) {
> +               up_read(&current->mm->mmap_sem);
> +               return -EINVAL;
> +       }
>         zc->length = min_t(unsigned long, zc->length, vma->vm_end - address);
>
>         tp = tcp_sk(sk);
> --
> 2.26.2.761.g0e0b3e54be-goog
>

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