ACK: [SRU H/I/OEM-5.14] NFSD: Fix exposure in nfsd4_decode_bitmap()

[Tim Gardner]

Acked-by: Tim Gardner <tim.gardner at canonical.com>

On 12/16/21 1:06 PM, Thadeu Lima de Souza Cascardo wrote:
> From: Chuck Lever <chuck.lever at oracle.com>
> 
> rtm at csail.mit.edu reports:
>> nfsd4_decode_bitmap4() will write beyond bmval[bmlen-1] if the RPC
>> directs it to do so. This can cause nfsd4_decode_state_protect4_a()
>> to write client-supplied data beyond the end of
>> nfsd4_exchange_id.spo_must_allow[] when called by
>> nfsd4_decode_exchange_id().
> 
> Rewrite the loops so nfsd4_decode_bitmap() cannot iterate beyond
> @bmlen.
> 
> Reported by: rtm at csail.mit.edu
> Fixes: d1c263a031e8 ("NFSD: Replace READ* macros in nfsd4_decode_fattr()")
> Signed-off-by: Chuck Lever <chuck.lever at oracle.com>
> Signed-off-by: J. Bruce Fields <bfields at redhat.com>
> (cherry picked from commit c0019b7db1d7ac62c711cda6b357a659d46428fe)
> CVE-2021-4090
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
> ---
>   fs/nfsd/nfs4xdr.c | 7 ++-----
>   1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index be64d3f5e411..0017da5bf23f 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -288,11 +288,8 @@ nfsd4_decode_bitmap4(struct nfsd4_compoundargs *argp, u32 *bmval, u32 bmlen)
>   	p = xdr_inline_decode(argp->xdr, count << 2);
>   	if (!p)
>   		return nfserr_bad_xdr;
> -	i = 0;
> -	while (i < count)
> -		bmval[i++] = be32_to_cpup(p++);
> -	while (i < bmlen)
> -		bmval[i++] = 0;
> +	for (i = 0; i < bmlen; i++)
> +		bmval[i] = (i < count) ? be32_to_cpup(p++) : 0;
>   
>   	return nfs_ok;
>   }
> 

-- 
-----------
Tim Gardner
Canonical, Inc