[PATCH 4.4 42/53] xfs: fix over-copying of getbmap parameters from userspace

Greg Kroah-Hartman
2017-06-05T16:22:27Z

From: Darrick J. Wong <darrick.wong@oracle.com>

commit be6324c00c4d1e0e665f03ed1fc18863a88da119 upstream.

In xfs_ioc_getbmap, we should only copy the fields of struct getbmap
from userspace, or else we end up copying random stack contents into the
kernel. struct getbmap is a strict subset of getbmapx, so a partial
structure copy should work fine.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/xfs/xfs_ioctl.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1379,10 +1379,11 @@ xfs_ioc_getbmap(
unsigned int cmd,
void __user *arg)
{
- struct getbmapx bmx;
+ struct getbmapx bmx = { 0 };
int error;

- if (copy_from_user(&bmx, arg, sizeof(struct getbmapx)))
+ /* struct getbmap is a strict subset of struct getbmapx. */
+ if (copy_from_user(&bmx, arg, offsetof(struct getbmapx, bmv_iflags)))
return -EFAULT;

if (bmx.bmv_count < 2)