| Message ID | 1460677712-26909-1-git-send-email-andreyu@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Apr 14, 2016 at 04:48:32PM -0700, Andrey Ulanov wrote: > +++ b/fs/namespace.c > @@ -1562,6 +1562,7 @@ void __detach_mounts(struct dentry *dentry) > goto out_unlock; > > lock_mount_hash(); > + event++; That part makes sense. > -/* > +/* > * Is the caller allowed to modify his namespace? > */ > static inline bool may_mount(void) > @@ -1765,6 +1766,7 @@ void drop_collected_mounts(struct vfsmount *mnt) > { > namespace_lock(); > lock_mount_hash(); > + event++; ... but what the hell is this one for? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Apr 14, 2016 at 5:50 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: >> + event++; > ... but what the hell is this one for? You're right this wasn't necessary. See updated patch. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/namespace.c b/fs/namespace.c index 4fb1691..b06bb9a 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1562,6 +1562,7 @@ void __detach_mounts(struct dentry *dentry) goto out_unlock; lock_mount_hash(); + event++; while (!hlist_empty(&mp->m_list)) { mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list); if (mnt->mnt.mnt_flags & MNT_UMOUNT) { @@ -1576,7 +1577,7 @@ out_unlock: namespace_unlock(); } -/* +/* * Is the caller allowed to modify his namespace? */ static inline bool may_mount(void) @@ -1765,6 +1766,7 @@ void drop_collected_mounts(struct vfsmount *mnt) { namespace_lock(); lock_mount_hash(); + event++; umount_tree(real_mount(mnt), UMOUNT_SYNC); unlock_mount_hash(); namespace_unlock();
This change fixes a problem originally reported at: https://github.com/coreos/bugs/issues/1153 You can find code that reproduces it at: https://github.com/coreos/bugs/issues/1153#issuecomment-210201681 - m_start() in fs/namespace.c expects that ns->event is incremented each time a mount added or removed from ns->list. - umount_tree() removes items from the list but does not increment event counter, expecting that it's done before the function is called. - There are some codepaths that call umount_tree() without updating "event" counter. e.g. from __detach_mounts(). - When this happens m_start may reuse a cached mount structure that no longer belongs to ns->list (i.e. use after free which usually leads to infinite loop). This change fixes the above problem by incrementing global event counter before invoking umount_tree(). Signed-off-by: Andrey Ulanov <andreyu@google.com> --- fs/namespace.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)