[PATCH 2/6] xfs: zero proper structure size for geometry calls CVE-2011-0711

paolo.pisati at canonical.com paolo.pisati at canonical.com
Mon Jul 4 09:53:36 UTC 2011

From: Alex Elder <aelder at sgi.com>

BugLink: http://bugs.launchpad.net/bugs/767740

Commit 493f3358cb289ccf716c5a14fa5bb52ab75943e5 added this call to
xfs_fs_geometry() in order to avoid passing kernel stack data back
to user space:

+       memset(geo, 0, sizeof(*geo));

Unfortunately, one of the callers of that function passes the
address of a smaller data type, cast to fit the type that
xfs_fs_geometry() requires.  As a result, this can happen:

Kernel panic - not syncing: stack-protector: Kernel stack is corrupted
in: f87aca93

Pid: 262, comm: xfs_fsr Not tainted 2.6.38-rc6-493f3358cb2+ #1
Call Trace:

[<c12991ac>] ? panic+0x50/0x150
[<c102ed71>] ? __stack_chk_fail+0x10/0x18
[<f87aca93>] ? xfs_ioc_fsgeometry_v1+0x56/0x5d [xfs]

Fix this by fixing that one caller to pass the right type and then
copy out the subset it is interested in.

Note: This patch is an alternative to one originally proposed by
Eric Sandeen.


Reported-by: Jeffrey Hundstad <jeffrey.hundstad at mnsu.edu>
Signed-off-by: Alex Elder <aelder at sgi.com>
Reviewed-by: Eric Sandeen <sandeen at redhat.com>
Tested-by: Jeffrey Hundstad <jeffrey.hundstad at mnsu.edu>
Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
 fs/xfs/linux-2.6/xfs_ioctl.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/linux-2.6/xfs_ioctl.c b/fs/xfs/linux-2.6/xfs_ioctl.c
index 2f79328..f70a1a7 100644
--- a/fs/xfs/linux-2.6/xfs_ioctl.c
+++ b/fs/xfs/linux-2.6/xfs_ioctl.c
@@ -1081,14 +1081,19 @@ xfs_ioc_fsgeometry_v1(
 	xfs_mount_t		*mp,
 	void			__user *arg)
-	xfs_fsop_geom_v1_t	fsgeo;
+	xfs_fsop_geom_t         fsgeo;
 	int			error;
-	error = xfs_fs_geometry(mp, (xfs_fsop_geom_t *)&fsgeo, 3);
+	error = xfs_fs_geometry(mp, &fsgeo, 3);
 	if (error)
 		return -error;
-	if (copy_to_user(arg, &fsgeo, sizeof(fsgeo)))
+	/*
+	 * Caller should have passed an argument of type
+	 * xfs_fsop_geom_v1_t.  This is a proper subset of the
+	 * xfs_fsop_geom_t that xfs_fs_geometry() fills in.
+	 */
+	if (copy_to_user(arg, &fsgeo, sizeof(xfs_fsop_geom_v1_t)))
 		return -XFS_ERROR(EFAULT);
 	return 0;

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