[PATCH 4.7 02/41] vfs: ioctl: prevent double-fetch in dedupe ioctl

[Greg Kroah-Hartman]

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

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

From: Scott Bauer <sba...@plzdonthack.me>

commit 10eec60ce79187686e052092e5383c99b4420a20 upstream.

This prevents a double-fetch from user space that can lead to to an
undersized allocation and heap overflow.

Fixes: 54dbc1517237 ("vfs: hoist the btrfs deduplication ioctl to the vfs")
Signed-off-by: Scott Bauer <sba...@plzdonthack.me>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 fs/ioctl.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -590,6 +590,7 @@ static long ioctl_file_dedupe_range(stru
                goto out;
        }
 
+       same->dest_count = count;
        ret = vfs_dedupe_file_range(file, same);
        if (ret)
                goto out;