From: Chuck Lever <chuck.lever@oracle.com>
Date: Thu, 1 Sep 2022 15:10:18 -0400
Subject: [PATCH] NFSD: Protect against send buffer overflow in NFSv2 READ
Git-commit: 401bc1f90874280a80b93f23be33a0e7e2d1f912
Patch-mainline: v6.1
References: bsc#1205128 CVE-2022-43945 bsc#1210124
Since before the git era, NFSD has conserved the number of pages
held by each nfsd thread by combining the RPC receive and send
buffers into a single array of pages. This works because there are
no cases where an operation needs a large RPC Call message and a
large RPC Reply at the same time.
Once an RPC Call has been received, svc_process() updates
svc_rqst::rq_res to describe the part of rq_pages that can be
used for constructing the Reply. This means that the send buffer
(rq_res) shrinks when the received RPC record containing the RPC
Call is large.
A client can force this shrinkage on TCP by sending a correctly-
formed RPC Call header contained in an RPC record that is
excessively large. The full maximum payload size cannot be
constructed in that case.
Cc: <stable@vger.kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: NeilBrown <neilb@suse.com>
---
fs/nfsd/nfsxdr.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/fs/nfsd/nfsxdr.c
+++ b/fs/nfsd/nfsxdr.c
@@ -239,16 +239,24 @@ nfssvc_decode_readargs(struct svc_rqst *
{
struct nfsd_readargs *args = rqstp->rq_argp;
unsigned int len;
+ unsigned int pages;
int v;
+
p = decode_fh(p, &args->fh);
if (!p)
return 0;
+ /* calculate available pages for reply body */
+ pages = (rqstp->rq_server->sv_max_mesg / PAGE_SIZE + 1);
+ pages -= (rqstp->rq_next_page - rqstp->rq_pages);
+
args->offset = ntohl(*p++);
len = args->count = ntohl(*p++);
p++; /* totalcount - unused */
len = min_t(unsigned int, len, NFSSVC_MAXBLKSIZE_V2);
+ len = min_t(unsigned int, len, pages * PAGE_SIZE);
+ args->count = len;
/* set up somewhere to store response.
* We take pages, put them on reslist and include in iovec