[PATCH 5.19 088/717] NFSD: Protect against send buffer overflow in NFSv3 READ

Greg Kroah-Hartman
2022-10-22T10:46:17Z

From: Chuck Lever <chuck.lever@oracle.com>

commit fa6be9cc6e80ec79892ddf08a8c10cabab9baf38 upstream.

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>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/nfsd/nfs3proc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -147,7 +147,6 @@ nfsd3_proc_read(struct svc_rqst *rqstp)
{
struct nfsd3_readargs *argp = rqstp->rq_argp;
struct nfsd3_readres *resp = rqstp->rq_resp;
- u32 max_blocksize = svc_max_payload(rqstp);
unsigned int len;
int v;

@@ -156,7 +155,8 @@ nfsd3_proc_read(struct svc_rqst *rqstp)
(unsigned long) argp->count,
(unsigned long long) argp->offset);

- argp->count = min_t(u32, argp->count, max_blocksize);
+ argp->count = min_t(u32, argp->count, svc_max_payload(rqstp));
+ argp->count = min_t(u32, argp->count, rqstp->rq_res.buflen);
if (argp->offset > (u64)OFFSET_MAX)
argp->offset = (u64)OFFSET_MAX;
if (argp->offset + argp->count > (u64)OFFSET_MAX)