[PATCH 5.13 215/351] sunrpc: Avoid a KASAN slab-out-of-bounds bug in xdr_set_page_base()

Greg Kroah-Hartman
2021-07-19T17:42:45Z

From: Anna Schumaker <Anna.Schumaker@Netapp.com>

[ Upstream commit 6d1c0f3d28f98ea2736128ed3e46821496dc3a8c ]

This seems to happen fairly easily during READ_PLUS testing on NFS v4.2.
I found that we could end up accessing xdr->buf->pages[pgnr] with a pgnr
greater than the number of pages in the array. So let's just return
early if we're setting base to a point at the end of the page data and
let xdr_set_tail_base() handle setting up the buffer pointers instead.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Fixes: 8d86e373b0ef ("SUNRPC: Clean up helpers xdr_set_iov() and xdr_set_page_base()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sunrpc/xdr.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 3964ff74ee51..ca10ba2626f2 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -1230,10 +1230,9 @@ static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
void *kaddr;

maxlen = xdr->buf->page_len;
- if (base >= maxlen) {
- base = maxlen;
- maxlen = 0;
- } else
+ if (base >= maxlen)
+ return 0;
+ else
maxlen -= base;
if (len > maxlen)
len = maxlen;
--
2.30.2