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

Steve French
2016-03-09T04:23:43Z

On Tue, Mar 8, 2016 at 9:47 PM, Ben Hutchings <ben@decadent.org.uk> wrote:
> 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?

Do you want to do the followon patch to check for that, or do you want me
to write up a small patch for that?

>> 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

--
Thanks,

Steve