[PATCH 3.18 10/29] PM / hibernate: Fix oops at snapshot_write()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

commit fc14eebfc20854a38fd9f1d93a42b1783dad4d17 upstream.

syzbot is reporting NULL pointer dereference at snapshot_write() [1].
This is because data->handle is zero-cleared by ioctl(SNAPSHOT_FREE).
Fix this by checking data_of(data->handle) != NULL before using it.

[1] https://syzkaller.appspot.com/bug?id=828a3c71bd344a6de8b6a31233d51a72099f27fd

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+ae590932da6e45d6564d@syzkaller.appspotmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/power/user.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -184,6 +184,11 @@ static ssize_t snapshot_write(struct fil
 		res = PAGE_SIZE - pg_offp;
 	}
 
+	if (!data_of(data->handle)) {
+		res = -EINVAL;
+		goto unlock;
+	}
+
 	res = simple_write_to_buffer(data_of(data->handle), res, &pg_offp,
 			buf, count);
 	if (res > 0)