ACK: [SRU B/D][PATCH 1/1] cifs: fix strcat buffer overflow and reduce raciness in smb21_set_oplock_level()

[Stefan Bader]

On 17.07.19 22:13, Guilherme G. Piccoli wrote:
> From: Christoph Probst <kernel at probst.it>
> 
> BugLink: https://bugs.launchpad.net/bugs/1824981
> 
> Change strcat to strncpy in the "None" case to fix a buffer overflow
> when cinode->oplock is reset to 0 by another thread accessing the same
> cinode. It is never valid to append "None" to any other message.
> 
> Consolidate multiple writes to cinode->oplock to reduce raciness.
> 
> Signed-off-by: Christoph Probst <kernel at probst.it>
> Reviewed-by: Pavel Shilovsky <pshilov at microsoft.com>
> Signed-off-by: Steve French <stfrench at microsoft.com>
> CC: Stable <stable at vger.kernel.org>
> (cherry picked from commit 6a54b2e002c9d00b398d35724c79f9fe0d9b38fb)
> Signed-off-by: Guilherme G. Piccoli <gpiccoli at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>  fs/cifs/smb2ops.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index f5eeecb5cbc3..24835e002941 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -1933,26 +1933,28 @@ smb21_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock,
>  		       unsigned int epoch, bool *purge_cache)
>  {
>  	char message[5] = {0};
> +	unsigned int new_oplock = 0;
>  
>  	oplock &= 0xFF;
>  	if (oplock == SMB2_OPLOCK_LEVEL_NOCHANGE)
>  		return;
>  
> -	cinode->oplock = 0;
>  	if (oplock & SMB2_LEASE_READ_CACHING_HE) {
> -		cinode->oplock |= CIFS_CACHE_READ_FLG;
> +		new_oplock |= CIFS_CACHE_READ_FLG;
>  		strcat(message, "R");
>  	}
>  	if (oplock & SMB2_LEASE_HANDLE_CACHING_HE) {
> -		cinode->oplock |= CIFS_CACHE_HANDLE_FLG;
> +		new_oplock |= CIFS_CACHE_HANDLE_FLG;
>  		strcat(message, "H");
>  	}
>  	if (oplock & SMB2_LEASE_WRITE_CACHING_HE) {
> -		cinode->oplock |= CIFS_CACHE_WRITE_FLG;
> +		new_oplock |= CIFS_CACHE_WRITE_FLG;
>  		strcat(message, "W");
>  	}
> -	if (!cinode->oplock)
> -		strcat(message, "None");
> +	if (!new_oplock)
> +		strncpy(message, "None", sizeof(message));
> +
> +	cinode->oplock = new_oplock;
>  	cifs_dbg(FYI, "%s Lease granted on inode %p\n", message,
>  		 &cinode->vfs_inode);
>  }
> 


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