Patch "NFSD: Protect against send buffer overflow in NFSv3 READ" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    NFSD: Protect against send buffer overflow in NFSv3 READ

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nfsd-protect-against-send-buffer-overflow-in-nfsv3-r.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 70c8857d58aed91598f46eab9e8541671ec22e86
Author: Chuck Lever <chuck.lever@xxxxxxxxxx>
Date:   Thu Sep 1 15:10:24 2022 -0400

    NFSD: Protect against send buffer overflow in NFSv3 READ
    
    [ Upstream commit fa6be9cc6e80ec79892ddf08a8c10cabab9baf38 ]
    
    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@xxxxxxxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index d808779ab4538..8679c41746027 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -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)




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