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NFSD: Protect against send buffer overflow in NFSv2 READ

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[ Upstream commit 401bc1f90874280a80b93f23be33a0e7e2d1f912 ]

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: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Chuck Lever 2022-09-01 15:10:18 -04:00 • committed by Ksawlii
parent 956015a28a
commit c15bc8a9c4
1 changed files with 1 additions and 0 deletions
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fs/nfsd/nfsproc.c
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@ -185,6 +185,7 @@ nfsd_proc_read(struct svc_rqst *rqstp)
argp->count, argp->offset);
argp->count = min_t(u32, argp->count, NFSSVC_MAXBLKSIZE_V2);
argp->count = min_t(u32, argp->count, rqstp->rq_res.buflen);
v = 0;
len = argp->count;