Re: [PATCH -next 2/5] nfs: fix possible null-ptr-deref when parsing param

[Jeff Layton]

On Mon, 2022-10-24 at 00:39 +0800, Hawkins Jiawei wrote:
> According to commit "vfs: parse: deal with zero length string value",
> kernel will set the param->string to null pointer in vfs_parse_fs_string()
> if fs string has zero length.
> 
> Yet the problem is that, nfs_fs_context_parse_param() will dereferences the
> param->string, without checking whether it is a null pointer, which may
> trigger a null-ptr-deref bug.
> 
> This patch solves it by adding sanity check on param->string
> in nfs_fs_context_parse_param().
> 
> Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx>
> ---
>  fs/nfs/fs_context.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
> index 4da701fd1424..0c330bc13ef2 100644
> --- a/fs/nfs/fs_context.c
> +++ b/fs/nfs/fs_context.c
> @@ -684,6 +684,8 @@ static int nfs_fs_context_parse_param(struct fs_context *fc,
>  			return ret;
>  		break;
>  	case Opt_vers:
> +		if (!param->string)
> +			goto out_invalid_value;
>  		trace_nfs_mount_assign(param->key, param->string);
>  		ret = nfs_parse_version_string(fc, param->string);
>  		if (ret < 0)
> @@ -696,6 +698,8 @@ static int nfs_fs_context_parse_param(struct fs_context *fc,
>  		break;
>  
>  	case Opt_proto:
> +		if (!param->string)
> +			goto out_invalid_value;
>  		trace_nfs_mount_assign(param->key, param->string);
>  		protofamily = AF_INET;
>  		switch (lookup_constant(nfs_xprt_protocol_tokens, param->string, -1)) {
> @@ -732,6 +736,8 @@ static int nfs_fs_context_parse_param(struct fs_context *fc,
>  		break;
>  
>  	case Opt_mountproto:
> +		if (!param->string)
> +			goto out_invalid_value;
>  		trace_nfs_mount_assign(param->key, param->string);
>  		mountfamily = AF_INET;
>  		switch (lookup_constant(nfs_xprt_protocol_tokens, param->string, -1)) {


Looks reasonable. I took a quick look for other fsparam_string values
that might not handle a NULL pointer correctly, but I didn't see any.

Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>