[PATCH] smb3: Fix out-of-bounds bug in SMB2_negotiate()

[Steve French]

merged into cifs-2.6.git for-next

On Mon, Feb 1, 2021 at 8:38 PM Gustavo A. R. Silva
<gustavoars at kernel.org> wrote:
>
> While addressing some warnings generated by -Warray-bounds, I found this
> bug that was introduced back in 2017:
>
>   CC [M]  fs/cifs/smb2pdu.o
> fs/cifs/smb2pdu.c: In function ‘SMB2_negotiate’:
> fs/cifs/smb2pdu.c:822:16: warning: array subscript 1 is above array bounds
> of ‘__le16[1]’ {aka ‘short unsigned int[1]’} [-Warray-bounds]
>   822 |   req->Dialects[1] = cpu_to_le16(SMB30_PROT_ID);
>       |   ~~~~~~~~~~~~~^~~
> fs/cifs/smb2pdu.c:823:16: warning: array subscript 2 is above array bounds
> of ‘__le16[1]’ {aka ‘short unsigned int[1]’} [-Warray-bounds]
>   823 |   req->Dialects[2] = cpu_to_le16(SMB302_PROT_ID);
>       |   ~~~~~~~~~~~~~^~~
> fs/cifs/smb2pdu.c:824:16: warning: array subscript 3 is above array bounds
> of ‘__le16[1]’ {aka ‘short unsigned int[1]’} [-Warray-bounds]
>   824 |   req->Dialects[3] = cpu_to_le16(SMB311_PROT_ID);
>       |   ~~~~~~~~~~~~~^~~
> fs/cifs/smb2pdu.c:816:16: warning: array subscript 1 is above array bounds
> of ‘__le16[1]’ {aka ‘short unsigned int[1]’} [-Warray-bounds]
>   816 |   req->Dialects[1] = cpu_to_le16(SMB302_PROT_ID);
>       |   ~~~~~~~~~~~~~^~~
>
> At the time, the size of array _Dialects_ was changed from 1 to 3 in struct
> validate_negotiate_info_req, and then in 2019 it was changed from 3 to 4,
> but those changes were never made in struct smb2_negotiate_req, which has
> led to a 3 and a half years old out-of-bounds bug in function
> SMB2_negotiate() (fs/cifs/smb2pdu.c).
>
> Fix this by increasing the size of array _Dialects_ in struct
> smb2_negotiate_req to 4.
>
> Fixes: 9764c02fcbad ("SMB3: Add support for multidialect negotiate (SMB2.1 and later)")
> Fixes: d5c7076b772a ("smb3: add smb3.1.1 to default dialect list")
> Cc: stable at vger.kernel.org
> Signed-off-by: Gustavo A. R. Silva <gustavoars at kernel.org>
> ---
>  fs/cifs/smb2pdu.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/cifs/smb2pdu.h b/fs/cifs/smb2pdu.h
> index d85edf5d1429..a5a9e33c0d73 100644
> --- a/fs/cifs/smb2pdu.h
> +++ b/fs/cifs/smb2pdu.h
> @@ -286,7 +286,7 @@ struct smb2_negotiate_req {
>         __le32 NegotiateContextOffset; /* SMB3.1.1 only. MBZ earlier */
>         __le16 NegotiateContextCount;  /* SMB3.1.1 only. MBZ earlier */
>         __le16 Reserved2;
> -       __le16 Dialects[1]; /* One dialect (vers=) at a time for now */
> +       __le16 Dialects[4]; /* BB expand this if autonegotiate > 4 dialects */
>  } __packed;
>
>  /* Dialects */
> --
> 2.27.0
>


-- 
Thanks,

Steve