netdev - Re: [PATCH v5 net] net: tap: NULL pointer derefence in dev_parse_header

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Message-ID: <CA+FuTSdp6_=4+J-ooz0vhjvthUAr6yLgQcAYR+Sgf=kbmzJV5A@mail.gmail.com>
Date:   Wed, 3 Aug 2022 07:12:40 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Cezar Bulinaru <cbulinaru@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v5 net] net: tap: NULL pointer derefence in
 dev_parse_header_protocol when skb->dev is null

On Wed, Aug 3, 2022 at 2:28 AM Cezar Bulinaru <cbulinaru@...il.com> wrote:
>
> Fixes a NULL pointer derefence bug triggered from tap driver.
> When tap_get_user calls virtio_net_hdr_to_skb the skb->dev is null
> (in tap.c skb->dev is set after the call to virtio_net_hdr_to_skb)
> virtio_net_hdr_to_skb calls dev_parse_header_protocol which
> needs skb->dev field to be valid.
>
> The line that trigers the bug is in dev_parse_header_protocol
> (dev is at offset 0x10 from skb and is stored in RAX register)
>   if (!dev->header_ops || !dev->header_ops->parse_protocol)
>   22e1:   mov    0x10(%rbx),%rax
>   22e5:   mov    0x230(%rax),%rax
>
> Setting skb->dev before the call in tap.c fixes the issue.
>
> BUG: kernel NULL pointer dereference, address: 0000000000000230
> RIP: 0010:virtio_net_hdr_to_skb.constprop.0+0x335/0x410 [tap]
> Code: c0 0f 85 b7 fd ff ff eb d4 41 39 c6 77 cf 29 c6 48 89 df 44 01 f6 e8 7a 79 83 c1 48 85 c0 0f 85 d9 fd ff ff eb b7 48 8b 43 10 <48> 8b 80 30 02 00 00 48 85 c0 74 55 48 8b 40 28 48 85 c0 74 4c 48
> RSP: 0018:ffffc90005c27c38 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff888298f25300 RCX: 0000000000000010
> RDX: 0000000000000005 RSI: ffffc90005c27cb6 RDI: ffff888298f25300
> RBP: ffffc90005c27c80 R08: 00000000ffffffea R09: 00000000000007e8
> R10: ffff88858ec77458 R11: 0000000000000000 R12: 0000000000000001
> R13: 0000000000000014 R14: ffffc90005c27e08 R15: ffffc90005c27cb6
> FS:  0000000000000000(0000) GS:ffff88858ec40000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000230 CR3: 0000000281408006 CR4: 00000000003706e0
> Call Trace:
>  tap_get_user+0x3f1/0x540 [tap]
>  tap_sendmsg+0x56/0x362 [tap]
>  ? get_tx_bufs+0xc2/0x1e0 [vhost_net]
>  handle_tx_copy+0x114/0x670 [vhost_net]
>  handle_tx+0xb0/0xe0 [vhost_net]
>  handle_tx_kick+0x15/0x20 [vhost_net]
>  vhost_worker+0x7b/0xc0 [vhost]
>  ? vhost_vring_call_reset+0x40/0x40 [vhost]
>  kthread+0xfa/0x120
>  ? kthread_complete_and_exit+0x20/0x20
>  ret_from_fork+0x1f/0x30
>
> Fixes: 924a9bc362a5 ("net: check if protocol extracted by virtio_net_hdr_set_proto is correct")
> Signed-off-by: Cezar Bulinaru <cbulinaru@...il.com>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>