[PATCH RFC 6/6] NFSD: Clamp WRITE offsets

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Ensure that a client cannot specify a WRITE range that falls in a
byte range outside what the kernel's internal types (such as loff_t,
which is signed) can represent. The kiocb iterators, invoked in
nfsd_vfs_write(), should properly limit write operations to within
the underlying file system's s_maxbytes.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 fs/nfsd/nfs3proc.c |    7 +++++++
 fs/nfsd/nfs4proc.c |    4 +++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 7bca219a8146..ba72bbff53a5 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -216,6 +216,12 @@ nfsd3_proc_write(struct svc_rqst *rqstp)
 				(unsigned long long) argp->offset,
 				argp->stable? " stable" : "");
 
+	resp->status = nfserr_fbig;
+	if (argp->offset >= OFFSET_MAX)
+		goto out;
+	if (argp->offset + argp->len >= OFFSET_MAX)
+		goto out;
+
 	fh_copy(&resp->fh, &argp->fh);
 	resp->committed = argp->stable;
 	nvecs = svc_fill_write_vector(rqstp, &argp->payload);
@@ -224,6 +230,7 @@ nfsd3_proc_write(struct svc_rqst *rqstp)
 				  rqstp->rq_vec, nvecs, &cnt,
 				  resp->committed, resp->verf);
 	resp->count = cnt;
+out:
 	return rpc_success;
 }
 
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index b8ac2b9bce74..2baf547b344f 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1022,7 +1022,9 @@ nfsd4_write(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	int nvecs;
 
 	if (write->wr_offset >= OFFSET_MAX)
-		return nfserr_inval;
+		return nfserr_fbig;
+	if (write->wr_offset + write->wr_buflen >= OFFSET_MAX)
+		return nfserr_fbig;
 
 	cnt = write->wr_buflen;
 	trace_nfsd_write_start(rqstp, &cstate->current_fh,




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