Re: [PATCH] NFSD: fix LISTXATTRS returning a short list with eof=TRUE

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2024-01-25 at 07:45 -0700, Jorge Mora wrote:
> If the XDR buffer is not large enough to fit all attributes
> and the remaining bytes left in the XDR buffer (xdrleft) is
> equal to the number of bytes for the current attribute, then
> the loop will prematurely exit without setting eof to FALSE.
> Also in this case, adding the eof flag to the buffer will
> make the reply 4 bytes larger than lsxa_maxcount.
> 
> Need to check if there are enough bytes to fit not only the
> next attribute name but also the eof as well.
> 
> Fixes: 23e50fe3a5e6 ("nfsd: implement the xattr functions and en/decode logic")
> Signed-off-by: Jorge Mora <mora@netapp.com>
> ---
>  fs/nfsd/nfs4xdr.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index 17e6404f4296..26993bf368fc 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -5182,7 +5182,8 @@ nfsd4_encode_listxattrs(struct nfsd4_compoundres *resp, __be32 nfserr,
>  
>  		slen -= XATTR_USER_PREFIX_LEN;
>  		xdrlen = 4 + ((slen + 3) & ~3);
> -		if (xdrlen > xdrleft) {
> +		/* Check if both entry and eof can fit in the XDR buffer */
> +		if (xdrlen + 4 > xdrleft) {
>  			if (count == 0) {
>  				/*
>  				 * Can't even fit the first attribute name.

Reviewed-by: Jeff Layton <jlayton@kernel.org>