[PATCH 4.6 95/96] vfs: ioctl: prevent double-fetch in dedupe ioctl

[Greg Kroah-Hartman]

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

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

From: Scott Bauer <sbauer@xxxxxxxxxxxxxx>

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 <sbauer@xxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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;