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NFSD: Protect against send buffer overflow in NFSv3 READ

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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>
This commit is contained in:
Chuck Lever 2022-09-01 15:10:24 -04:00
parent 401bc1f908
commit fa6be9cc6e
1 changed files with 2 additions and 2 deletions
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4
fs/nfsd/nfs3proc.c
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@ -150,7 +150,6 @@ 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;
@ -159,7 +158,8 @@ 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)