Re: [PATCH 4.4 13/74] cifs: fix out-of-bounds access in lease parsing

[Ben Hutchings <ben@decadent.org.uk>]

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On Mon, 2016-03-07 at 16:02 -0800, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Justin Maggard <jmaggard10@gmail.com>
> 
> commit deb7deff2f00bdbbcb3d560dad2a89ef37df837d upstream.
> 
> When opening a file, SMB2_open() attempts to parse the lease state from the
> SMB2 CREATE Response.  However, the parsing code was not careful to ensure
> that the create contexts are not empty or invalid, which can lead to out-
> of-bounds memory access.  This can be seen easily by trying
> to read a file from a OSX 10.11 SMB3 server.  Here is sample crash output:
> 
> BUG: unable to handle kernel paging request at ffff8800a1a77cc6
> IP: [] SMB2_open+0x804/0x960
> PGD 8f77067 PUD 0
> Oops: 0000 [#1] SMP
> Modules linked in:
> CPU: 3 PID: 2876 Comm: cp Not tainted 4.5.0-rc3.x86_64.1+ #14
> Hardware name: NETGEAR ReadyNAS 314          /ReadyNAS 314          , BIOS 4.6.5 10/11/2012
> task: ffff880073cdc080 ti: ffff88005b31c000 task.ti: ffff88005b31c000
> RIP: 0010:[]  [] SMB2_open+0x804/0x960
> RSP: 0018:ffff88005b31fa08  EFLAGS: 00010282
> RAX: 0000000000000015 RBX: 0000000000000000 RCX: 0000000000000006
> RDX: 0000000000000000 RSI: 0000000000000246 RDI: ffff88007eb8c8b0
> RBP: ffff88005b31fad8 R08: 666666203d206363 R09: 6131613030383866
> R10: 3030383866666666 R11: 00000000000002b0 R12: ffff8800660fd800
> R13: ffff8800a1a77cc2 R14: 00000000424d53fe R15: ffff88005f5a28c0
> FS:  00007f7c8a2897c0(0000) GS:ffff88007eb80000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: ffff8800a1a77cc6 CR3: 000000005b281000 CR4: 00000000000006e0
> Stack:
>  ffff88005b31fa70 ffffffff88278789 00000000000001d3 ffff88005f5a2a80
>  ffffffff00000003 ffff88005d029d00 ffff88006fde05a0 0000000000000000
>  ffff88005b31fc78 ffff88006fde0780 ffff88005b31fb2f 0000000100000fe0
> Call Trace:
>  [] ? cifsConvertToUTF16+0x159/0x2d0
>  [] smb2_open_file+0x98/0x210
>  [] ? __kmalloc+0x1c/0xe0
>  [] cifs_open+0x2a4/0x720
>  [] do_dentry_open+0x1ff/0x310
>  [] ? cifsFileInfo_get+0x30/0x30
>  [] vfs_open+0x52/0x60
>  [] path_openat+0x170/0xf70
>  [] ? remove_wait_queue+0x48/0x50
>  [] do_filp_open+0x79/0xd0
>  [] ? __alloc_fd+0x3a/0x170
>  [] do_sys_open+0x114/0x1e0
>  [] SyS_open+0x19/0x20
>  [] entry_SYSCALL_64_fastpath+0x12/0x6a
> Code: 4d 8d 6c 07 04 31 c0 4c 89 ee e8 47 6f e5 ff 31 c9 41 89 ce 44 89 f1 48 c7 c7 28 b1 bd 88 31 c0 49 01 cd 4c 89 ee e8 2b 6f e5 ff <45> 0f b7 75 04 48 c7 c7 31 b1 bd 88 31 c0 4d 01 ee 4c 89 f6 e8
> RIP  [] SMB2_open+0x804/0x960
>  RSP 
> CR2: ffff8800a1a77cc6
> ---[ end trace d9f69ba64feee469 ]---
> 
> Signed-off-by: Justin Maggard <jmaggard@netgear.com>
> Signed-off-by: Steve French <smfrench@gmail.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> ---
>  fs/cifs/smb2pdu.c |   24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> --- a/fs/cifs/smb2pdu.c
> +++ b/fs/cifs/smb2pdu.c
> @@ -1109,21 +1109,25 @@ parse_lease_state(struct TCP_Server_Info
>  {
>  	char *data_offset;
>  	struct create_context *cc;
> -	unsigned int next = 0;
> +	unsigned int next;
> +	unsigned int remaining;
>  	char *name;
>  
>  	data_offset = (char *)rsp + 4 + le32_to_cpu(rsp->CreateContextsOffset);
> +	remaining = le32_to_cpu(rsp->CreateContextsLength);

What if remaining is > the response length?

>  	cc = (struct create_context *)data_offset;
> -	do {
> -		cc = (struct create_context *)((char *)cc + next);
> +	while (remaining >= sizeof(struct create_context)) {
>  		name = le16_to_cpu(cc->NameOffset) + (char *)cc;
> -		if (le16_to_cpu(cc->NameLength) != 4 ||
> -		    strncmp(name, "RqLs", 4)) {
> -			next = le32_to_cpu(cc->Next);
> -			continue;
> -		}
> -		return server->ops->parse_lease_buf(cc, epoch);
> -	} while (next != 0);
> +		if (le16_to_cpu(cc->NameLength) == 4 &&
> +		    strncmp(name, "RqLs", 4) == 0)
> +			return server->ops->parse_lease_buf(cc, epoch);
> +
> +		next = le32_to_cpu(cc->Next);
> +		if (!next)
> +			break;
> +		remaining -= next;

What if next > remaining?

This change seems to be only scratching the surface of the security
failure here.

Ben.

> +		cc = (struct create_context *)((char *)cc + next);
> +	}
>  
>  	return 0;
>  }

-- 
Ben Hutchings
When in doubt, use brute force. - Ken Thompson

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