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Subject: [PATCH v1] SUNRPC: Fix READ_PLUS crasher
From:   Chuck Lever <chuck.lever@oracle.com>
To:     linux-nfs@vger.kernel.org
Cc:     anna.schumaker@netapp.com, bfields@fieldses.org, zlang@redhat.com
Date:   Thu, 30 Jun 2022 13:24:20 -0400
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Looks like there are still cases when "space_left - frag1bytes" can
legitimately exceed PAGE_SIZE. Ensure that xdr->end always remains
within the current encode buffer.

Reported-by: Bruce Fields <bfields@fieldses.org>
Reported-by: Zorro Lang <zlang@redhat.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216151
Fixes: 6c254bf3b637 ("SUNRPC: Fix the calculation of xdr->end in xdr_get_next_encode_buffer()")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xdr.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Hi-

I had a few minutes yesterday afternoon to look into this one. The
following one-liner seems to address the issue and passes my smoke
tests with NFSv4.1/TCP and NFSv3/RDMA. Any thoughts?


diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index f87a2d8f23a7..916659be2774 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -987,7 +987,7 @@ static noinline __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
 	if (space_left - nbytes >= PAGE_SIZE)
 		xdr->end = p + PAGE_SIZE;
 	else
-		xdr->end = p + space_left - frag1bytes;
+		xdr->end = p + min_t(int, space_left - frag1bytes, PAGE_SIZE);
 
 	xdr->buf->page_len += frag2bytes;
 	xdr->buf->len += nbytes;