linux-kernel - Re: [PATCH v2] nfsd: prevent integer overflow in decode_cb

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Message-ID: <C185CD71-0AF6-4D83-AEE5-F8C87EEDE86B@oracle.com>
Date: Thu, 19 Sep 2024 14:02:19 +0000
From: Chuck Lever III <chuck.lever@...cle.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
CC: Jeff Layton <jlayton@...nel.org>, Neil Brown <neilb@...e.de>,
        Olga
 Kornievskaia <okorniev@...hat.com>, Dai Ngo <dai.ngo@...cle.com>,
        Tom Talpey
	<tom@...pey.com>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        Linux
 Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH v2] nfsd: prevent integer overflow in
 decode_cb_compound4res()



> On Sep 19, 2024, at 1:12 AM, Dan Carpenter <dan.carpenter@...aro.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@...aro.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