From: Chuck Lever <chuck.lever@oracle.com>
Date: Thu, 1 Sep 2022 15:09:59 -0400
Subject: [PATCH] SUNRPC: Fix svcxdr_init_encode's buflen calculation
Git-commit: 1242a87da0d8cd2a428e96ca68e7ea899b0f4624
Patch-mainline: v6.1
References: bsc#1205128 CVE-2022-43945

Commit 2825a7f90753 ("nfsd4: allow encoding across page boundaries")
added an explicit computation of the remaining length in the rq_res
XDR buffer.

The computation appears to suffer from an "off-by-one" bug. Because
buflen is too large by one page, XDR encoding can run off the end of
the send buffer by eventually trying to use the struct page address
in rq_page_end, which always contains NULL.

Fixes: bddfdbcddbe2 ("NFSD: Extract the svcxdr_init_encode() helper")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 include/linux/sunrpc/svc.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -610,7 +610,7 @@ static inline void svcxdr_init_encode(st
 	xdr->end = resv->iov_base + PAGE_SIZE - rqstp->rq_auth_slack;
 	buf->len = resv->iov_len;
 	xdr->page_ptr = buf->pages - 1;
-	buf->buflen = PAGE_SIZE * (1 + rqstp->rq_page_end - buf->pages);
+	buf->buflen = PAGE_SIZE * (rqstp->rq_page_end - buf->pages);
 	buf->buflen -= rqstp->rq_auth_slack;
 	xdr->rqst = NULL;
 }