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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Chuck Lever <chuck.lever@oracle.com>,
        NeilBrown <neilb@suse.de>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.18 205/339] SUNRPC: Fix the calculation of xdr->end in xdr_get_next_encode_buffer()
Date:   Mon, 13 Jun 2022 12:10:30 +0200
Message-Id: <20220613094932.882613530@linuxfoundation.org>
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From: Chuck Lever <chuck.lever@oracle.com>

[ Upstream commit 6c254bf3b637dd4ef4f78eb78c7447419c0161d7 ]

I found that NFSD's new NFSv3 READDIRPLUS XDR encoder was screwing up
right at the end of the page array. xdr_get_next_encode_buffer() does
not compute the value of xdr->end correctly:

 * The check to see if we're on the final available page in xdr->buf
   needs to account for the space consumed by @nbytes.

 * The new xdr->end value needs to account for the portion of @nbytes
   that is to be encoded into the previous buffer.

Fixes: 2825a7f90753 ("nfsd4: allow encoding across page boundaries")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Reviewed-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/sunrpc/xdr.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index df194cc07035..b57cf9df4de8 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -979,7 +979,11 @@ static __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
 	 */
 	xdr->p = (void *)p + frag2bytes;
 	space_left = xdr->buf->buflen - xdr->buf->len;
-	xdr->end = (void *)p + min_t(int, space_left, PAGE_SIZE);
+	if (space_left - nbytes >= PAGE_SIZE)
+		xdr->end = (void *)p + PAGE_SIZE;
+	else
+		xdr->end = (void *)p + space_left - frag1bytes;
+
 	xdr->buf->page_len += frag2bytes;
 	xdr->buf->len += nbytes;
 	return p;
-- 
2.35.1