linux.git/fs/namespace.c, branch v3.13

vfs: Fix a regression in mounting proc

2013-11-27T04:54:52+00:00

Gao feng  reported that commit
e51db73532955dc5eaba4235e62b74b460709d5b
userns: Better restrictions on when proc and sysfs can be mounted
caused a regression on mounting a new instance of proc in a mount
namespace created with user namespace privileges, when binfmt_misc
is mounted on /proc/sys/fs/binfmt_misc.

This is an unintended regression caused by the absolutely bogus empty
directory check in fs_fully_visible.  The check fs_fully_visible replaced
didn't even bother to attempt to verify proc was fully visible and
hiding proc files with any kind of mount is rare.  So for now fix
the userspace regression by allowing directory with nlink == 1
as /proc/sys/fs/binfmt_misc has.

I will have a better patch but it is not stable material, or
last minute kernel material.  So it will have to wait.

Cc: stable@vger.kernel.org
Acked-by: Serge Hallyn 
Acked-by: Gao feng 
Tested-by: Gao feng 
Signed-off-by: "Eric W. Biederman"

RCU'd vfsmounts

2013-11-09T05:16:19+00:00

* RCU-delayed freeing of vfsmounts
* vfsmount_lock replaced with a seqlock (mount_lock)
* sequence number from mount_lock is stored in nameidata->m_seq and
used when we exit RCU mode
* new vfsmount flag - MNT_SYNC_UMOUNT.  Set by umount_tree() when its
caller knows that vfsmount will have no surviving references.
* synchronize_rcu() done between unlocking namespace_sem in namespace_unlock()
and doing pending mntput().
* new helper: legitimize_mnt(mnt, seq).  Checks the mount_lock sequence
number against seq, then grabs reference to mnt.  Then it rechecks mount_lock
again to close the race and either returns success or drops the reference it
has acquired.  The subtle point is that in case of MNT_SYNC_UMOUNT we can
simply decrement the refcount and sod off - aforementioned synchronize_rcu()
makes sure that final mntput() won't come until we leave RCU mode.  We need
that, since we don't want to end up with some lazy pathwalk racing with
umount() and stealing the final mntput() from it - caller of umount() may
expect it to return only once the fs is shut down and we don't want to break
that.  In other cases (i.e. with MNT_SYNC_UMOUNT absent) we have to do
full-blown mntput() in case of mount_lock sequence number mismatch happening
just as we'd grabbed the reference, but in those cases we won't be stealing
the final mntput() from anything that would care.
* mntput_no_expire() doesn't lock anything on the fast path now.  Incidentally,
SMP and UP cases are handled the same way - no ifdefs there.
* normal pathname resolution does *not* do any writes to mount_lock.  It does,
of course, bump the refcounts of vfsmount and dentry in the very end, but that's
it.

Signed-off-by: Al Viro

split __lookup_mnt() in two functions

2013-10-25T03:35:00+00:00

Instead of passing the direction as argument (and checking it on every
step through the hash chain), just have separate __lookup_mnt() and
__lookup_mnt_last().  And use the standard iterators...

Signed-off-by: Al Viro

new helpers: lock_mount_hash/unlock_mount_hash

2013-10-25T03:34:59+00:00

aka br_write_{lock,unlock} of vfsmount_lock.  Inlines in fs/mount.h,
vfsmount_lock extern moved over there as well.

Signed-off-by: Al Viro

namespace.c: get rid of mnt_ghosts

2013-10-25T03:34:58+00:00

Signed-off-by: Al Viro

fold dup_mnt_ns() into its only surviving caller

2013-10-25T03:34:58+00:00

should've been done 6 years ago...

Signed-off-by: Al Viro

mnt_set_expiry() doesn't need vfsmount_lock

2013-10-25T03:34:57+00:00

->mnt_expire is protected by namespace_sem

Signed-off-by: Al Viro

finish_automount() doesn't need vfsmount_lock for removal from expiry list

2013-10-25T03:34:57+00:00

Signed-off-by: Al Viro

fs/namespace.c: bury long-dead define

2013-10-25T03:34:57+00:00

MNT_WRITER_UNDERFLOW_LIMIT has been missed 4 years ago when it became unused.

Signed-off-by: Al Viro

fold mntfree() into mntput_no_expire()

2013-10-25T03:34:56+00:00

Signed-off-by: Al Viro