Re: [PATCH v2] ocfs2: mount fails with buffer overflow in strlen

[Joseph Qi]

On 9/30/21 2:06 AM, Valentin Vidic wrote:
> Starting with kernel 5.11 built with CONFIG_FORTIFY_SOURCE mouting an
> ocfs2 filesystem with either o2cb or pcmk cluster stack fails with the
> trace below. Problem seems to be that strings for cluster stack and
> cluster name are not guaranteed to be null terminated in the disk
> representation, while strlcpy assumes that the source string is always
> null terminated. This causes a read outside of the source string
> triggering the buffer overflow detection.
> 
> detected buffer overflow in strlen
> ------------[ cut here ]------------
> kernel BUG at lib/string.c:1149!
> invalid opcode: 0000 [#1] SMP PTI
> CPU: 1 PID: 910 Comm: mount.ocfs2 Not tainted 5.14.0-1-amd64 #1
>   Debian 5.14.6-2
> RIP: 0010:fortify_panic+0xf/0x11
> ...
> Call Trace:
>  ocfs2_initialize_super.isra.0.cold+0xc/0x18 [ocfs2]
>  ocfs2_fill_super+0x359/0x19b0 [ocfs2]
>  mount_bdev+0x185/0x1b0
>  ? ocfs2_remount+0x440/0x440 [ocfs2]
>  legacy_get_tree+0x27/0x40
>  vfs_get_tree+0x25/0xb0
>  path_mount+0x454/0xa20
>  __x64_sys_mount+0x103/0x140
>  do_syscall_64+0x3b/0xc0
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Signed-off-by: Valentin Vidic <vvidic@xxxxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
> ---
> v2: update description, add comment, drop null termination
> 
>  fs/ocfs2/super.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> index c86bd4e60e20..5c914ce9b3ac 100644
> --- a/fs/ocfs2/super.c
> +++ b/fs/ocfs2/super.c
> @@ -2167,11 +2167,17 @@ static int ocfs2_initialize_super(struct super_block *sb,
>  	}
>  
>  	if (ocfs2_clusterinfo_valid(osb)) {
> +		/*
> +		 * ci_stack and ci_cluster in ocfs2_cluster_info may not be null
> +		 * terminated, so make sure no overflow happens here by using
> +		 * memcpy. Destination strings will always be null terminated
> +		 * because osb is allocated using kzalloc.
> +		 */
>  		osb->osb_stackflags =
>  			OCFS2_RAW_SB(di)->s_cluster_info.ci_stackflags;
> -		strlcpy(osb->osb_cluster_stack,
> +		memcpy(osb->osb_cluster_stack,
>  		       OCFS2_RAW_SB(di)->s_cluster_info.ci_stack,
> -		       OCFS2_STACK_LABEL_LEN + 1);
> +		       OCFS2_STACK_LABEL_LEN);
>  		if (strlen(osb->osb_cluster_stack) != OCFS2_STACK_LABEL_LEN) {
>  			mlog(ML_ERROR,
>  			     "couldn't mount because of an invalid "
> @@ -2180,9 +2186,9 @@ static int ocfs2_initialize_super(struct super_block *sb,
>  			status = -EINVAL;
>  			goto bail;
>  		}
> -		strlcpy(osb->osb_cluster_name,
> +		memcpy(osb->osb_cluster_name,
>  			OCFS2_RAW_SB(di)->s_cluster_info.ci_cluster,
> -			OCFS2_CLUSTER_NAME_LEN + 1);
> +			OCFS2_CLUSTER_NAME_LEN);
>  	} else {
>  		/* The empty string is identical with classic tools that
>  		 * don't know about s_cluster_info. */
>