swsusp: Fix userland interface

Fix oops caused by 'cat /dev/snapshot', reported by Arkadiusz Miskiewicz,
and make it impossible to thaw tasks with the help of the swsusp userland
interface while there is a snapshot image ready to save.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/kernel/power/user.c b/kernel/power/user.c
index 24d7d78e6f42..d65305b515b1 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -99,6 +99,8 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf,
         ssize_t res;
 
         data = filp->private_data;
+        if (!data->ready)
+                return -ENODATA;
         res = snapshot_read_next(&data->handle, count);
         if (res > 0) {
                 if (copy_to_user(buf, data_of(data->handle), res))
@@ -245,7 +247,7 @@ static int snapshot_ioctl(struct inode *inode, struct file *filp,
                 break;
 
         case SNAPSHOT_UNFREEZE:
-                if (!data->frozen)
+                if (!data->frozen || data->ready)
                         break;
                 mutex_lock(&pm_mutex);
                 thaw_processes();