linux-kernel - [PATCH 4.19 07/72] 9p/xen: fix check for xenbus_read error in front

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Message-Id: <20190702080124.947283085@linuxfoundation.org>
Date:   Tue,  2 Jul 2019 10:01:08 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Dominique Martinet <dominique.martinet@....fr>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Latchesar Ionkov <lucho@...kov.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 07/72] 9p/xen: fix check for xenbus_read error in front_probe

[ Upstream commit 2f9ad0ac947ccbe3ffe7c6229c9330f2a7755f64 ]

If the xen bus exists but does not expose the proper interface, it is
possible to get a non-zero length but still some error, leading to
strcmp failing trying to load invalid memory addresses e.g.
fffffffffffffffe.

There is then no need to check length when there is no error, as the
xenbus driver guarantees that the string is nul-terminated.

Link: http://lkml.kernel.org/r/1534236007-10170-1-git-send-email-asmadeus@codewreck.org
Signed-off-by: Dominique Martinet <dominique.martinet@....fr>
Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>
Cc: Eric Van Hensbergen <ericvh@...il.com>
Cc: Latchesar Ionkov <lucho@...kov.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/9p/trans_xen.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
index c2d54ac76bfd..843cb823d9b9 100644
--- a/net/9p/trans_xen.c
+++ b/net/9p/trans_xen.c
@@ -391,8 +391,8 @@ static int xen_9pfs_front_probe(struct xenbus_device *dev,
 	unsigned int max_rings, max_ring_order, len = 0;
 
 	versions = xenbus_read(XBT_NIL, dev->otherend, "versions", &len);
-	if (!len)
-		return -EINVAL;
+	if (IS_ERR(versions))
+		return PTR_ERR(versions);
 	if (strcmp(versions, "1")) {
 		kfree(versions);
 		return -EINVAL;
-- 
2.20.1