From 75d9de25a6f833dd0701ca546ac926cabff2b5af Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Thu, 1 Sep 2022 15:10:24 -0400 Subject: [PATCH] NFSD: Protect against send buffer overflow in NFSv3 READ 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: Signed-off-by: Chuck Lever Reviewed-by: Jeff Layton Signed-off-by: Chuck Lever Signed-off-by: Greg Kroah-Hartman --- fs/nfsd/nfs3proc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c index 4218a0a..eaf785a 100644 --- a/fs/nfsd/nfs3proc.c +++ b/fs/nfsd/nfs3proc.c @@ -146,7 +146,6 @@ 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; @@ -155,7 +154,8 @@ 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) -- 2.7.4