diff options
| author | Eric W. Biederman <ebiederm@xmission.com> | 2017-01-03 14:18:43 +1300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-01-19 20:17:21 +0100 |
| commit | 4a6716f165179679ee418b79445aa4031118ecd1 (patch) | |
| tree | 7758d19ab9320ad2855815a51e8290793992052a /fs/dcache.c | |
| parent | 836fd7c9e6e6bf18d8d0ced59019455de648cd31 (diff) | |
mnt: Protect the mountpoint hashtable with mount_lock
commit 3895dbf8985f656675b5bde610723a29cbce3fa7 upstream.
Protecting the mountpoint hashtable with namespace_sem was sufficient
until a call to umount_mnt was added to mntput_no_expire. At which
point it became possible for multiple calls of put_mountpoint on
the same hash chain to happen on the same time.
Kristen Johansen <kjlx@templeofstupid.com> reported:
> This can cause a panic when simultaneous callers of put_mountpoint
> attempt to free the same mountpoint. This occurs because some callers
> hold the mount_hash_lock, while others hold the namespace lock. Some
> even hold both.
>
> In this submitter's case, the panic manifested itself as a GP fault in
> put_mountpoint() when it called hlist_del() and attempted to dereference
> a m_hash.pprev that had been poisioned by another thread.
Al Viro observed that the simple fix is to switch from using the namespace_sem
to the mount_lock to protect the mountpoint hash table.
I have taken Al's suggested patch moved put_mountpoint in pivot_root
(instead of taking mount_lock an additional time), and have replaced
new_mountpoint with get_mountpoint a function that does the hash table
lookup and addition under the mount_lock. The introduction of get_mounptoint
ensures that only the mount_lock is needed to manipulate the mountpoint
hashtable.
d_set_mounted is modified to only set DCACHE_MOUNTED if it is not
already set. This allows get_mountpoint to use the setting of
DCACHE_MOUNTED to ensure adding a struct mountpoint for a dentry
happens exactly once.
Fixes: ce07d891a089 ("mnt: Honor MNT_LOCKED when detaching mounts")
Reported-by: Krister Johansen <kjlx@templeofstupid.com>
Suggested-by: Al Viro <viro@ZenIV.linux.org.uk>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/dcache.c')
| -rw-r--r-- | fs/dcache.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index 71b6056ad35d..849c1c1e787b 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1322,8 +1322,11 @@ int d_set_mounted(struct dentry *dentry) } spin_lock(&dentry->d_lock); if (!d_unlinked(dentry)) { - dentry->d_flags |= DCACHE_MOUNTED; - ret = 0; + ret = -EBUSY; + if (!d_mountpoint(dentry)) { + dentry->d_flags |= DCACHE_MOUNTED; + ret = 0; + } } spin_unlock(&dentry->d_lock); out: |