Re: [PATCH] nfs: Fix getxattr kernel panic and memory overflow

[Trond Myklebust <trondmy@hammerspace.com>]

On Wed, 2020-08-05 at 12:23 -0500, Jeffrey Mitchell wrote:
> Move the buffer size check to decode_attr_security_label() before
> memcpy()
> Only call memcpy() if the buffer is large enough
> 
> Signed-off-by: Jeffrey Mitchell <jeffrey.mitchell@starlab.io>
> ---
>  fs/nfs/nfs4proc.c | 2 --
>  fs/nfs/nfs4xdr.c  | 5 ++++-
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> index 2e2dac29a9e9..45e0585e0667 100644
> --- a/fs/nfs/nfs4proc.c
> +++ b/fs/nfs/nfs4proc.c
> @@ -5845,8 +5845,6 @@ static int _nfs4_get_security_label(struct
> inode *inode, void *buf,
>  		return ret;
>  	if (!(fattr.valid & NFS_ATTR_FATTR_V4_SECURITY_LABEL))
>  		return -ENOENT;
> -	if (buflen < label.len)
> -		return -ERANGE;
>  	return 0;
>  }
>  
> diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
> index 47817ef0aadb..50162e0a959c 100644
> --- a/fs/nfs/nfs4xdr.c
> +++ b/fs/nfs/nfs4xdr.c
> @@ -4166,7 +4166,10 @@ static int decode_attr_security_label(struct
> xdr_stream *xdr, uint32_t *bitmap,
>  			return -EIO;
>  		if (len < NFS4_MAXLABELLEN) {
>  			if (label) {
> -				memcpy(label->label, p, len);
> +				if (label->len && label->len < len)
> +					return -ERANGE;
> +				if (label->len)
> +					memcpy(label->label, p, len);

Just a heads up that I fixed this to avoid the duplicate test of label-
>len != 0 and I added a Fixes: before applying.

>  				label->len = len;
>  				label->pi = pi;
>  				label->lfs = lfs;
-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com