do_change_type() is buggy when passed multiple MS_* flags. Discovered
because mount(8) incorrectly adds MS_RDONLY flag to
shared/slave/private/unbindable mounts. Karel Zak will fix the
mount(8) bug shortly.
A test program is attached. Against Viro's #untested branch.
-VAL
commit 208ca52f69ea53cf0723b8492fe54ebf9a3bf36a
Author: Valerie Aurora <vaurora@xxxxxxxxxx>
Date: Thu Aug 26 11:07:22 2010 -0700
VFS: Sanity check mount flags passed to change_mnt_propagation()
Sanity check the flags passed to change_mnt_propagation(). Exactly
one flag should be set. Return EINVAL otherwise.
Userspace can pass in arbitrary combinations of MS_* flags to mount().
do_change_type() is called if any of MS_SHARED, MS_PRIVATE, MS_SLAVE,
or MS_UNBINDABLE is set. do_change_type() clears MS_REC and then
calls change_mnt_propagation() with the rest of the user-supplied
flags. change_mnt_propagation() clearly assumes only one flag is set
but do_change_type() does not check that this is true. For example,
mount() with flags MS_SHARED | MS_RDONLY does not actually make the
mount shared or read-only but does clear MNT_UNBINDABLE.
Signed-off-by: Valerie Aurora <vaurora@xxxxxxxxxx>
diff --git a/fs/namespace.c b/fs/namespace.c
index de402eb..4987c4c 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1484,13 +1484,32 @@ out_unlock:
}
/*
+ * Sanity check the flags to change_mnt_propagation.
+ */
+
+static int flags_to_propagation_type(int flags) {
+ int type = flags & ~MS_REC;
+
+ /* Fail if any non-propagation flags are set */
+ if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
+ return 0;
+ /* Only one propagation flag should be set */
+ if (((type & (MS_SHARED)) && (type & ~MS_SHARED)) ||
+ ((type & (MS_PRIVATE)) && (type & ~MS_PRIVATE)) ||
+ ((type & (MS_SLAVE)) && (type & ~MS_SLAVE)) ||
+ ((type & (MS_UNBINDABLE)) && (type & ~MS_UNBINDABLE)))
+ return 0;
+ return type;
+}
+
+/*
* recursively change the type of the mountpoint.
*/
static int do_change_type(struct path *path, int flag)
{
struct vfsmount *m, *mnt = path->mnt;
int recurse = flag & MS_REC;
- int type = flag & ~MS_REC;
+ int type;
int err = 0;
if (!capable(CAP_SYS_ADMIN))
@@ -1499,6 +1518,10 @@ static int do_change_type(struct path *path, int flag)
if (path->dentry != path->mnt->mnt_root)
return -EINVAL;
+ type = flags_to_propagation_type(flag);
+ if (!type)
+ return -EINVAL;
+
down_write(&namespace_sem);
if (type == MS_SHARED) {
err = invent_group_ids(mnt, recurse);
--
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