Re: [PATCH v2] nfsd: prevent integer overflow in decode_cb_compound4res()

[Chuck Lever III <chuck.lever@oracle.com>]

> On Sep 19, 2024, at 1:12 AM, Dan Carpenter <dan.carpenter@linaro.org> wrote:
> 
> If "length" is >= U32_MAX - 3 then the "length + 4" addition can result
> in an integer overflow.  The impact of this bug is not totally clear to
> me, but it's safer to not allow the integer overflow.
> 
> Check that "length" is valid right away before doing any math.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> ---
> v2: Check that "len" is valid instead of just checking for integer
>    overflows.
> 
> fs/nfsd/nfs4callback.c | 2 ++
> 1 file changed, 2 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
> index 43b8320c8255..0f5b7b6fba74 100644
> --- a/fs/nfsd/nfs4callback.c
> +++ b/fs/nfsd/nfs4callback.c
> @@ -317,6 +317,8 @@ static int decode_cb_compound4res(struct xdr_stream *xdr,
> hdr->status = be32_to_cpup(p++);
> /* Ignore the tag */
> length = be32_to_cpup(p++);
> + if (unlikely(length > xdr->buf->len))
> + goto out_overflow;
> p = xdr_inline_decode(xdr, length + 4);
> if (unlikely(p == NULL))
> goto out_overflow;
> -- 
> 2.34.1
> 

Hi Dan, I've already gone with

https://lore.kernel.org/linux-nfs/172658972371.2454.15715383792386404543.stgit@oracle-102.chuck.lever.oracle.com.nfsv4.dev/T/#u

Let me know if that doesn't make sense.

--
Chuck Lever