autofs4: fix indirect mount pending expire race
The selection of a dentry for expiration and the setting of the
AUTOFS_INF_EXPIRING flag isn't done atomically which can lead to lookups
walking into an expiring mount.
What happens is that an expire is initiated by the daemon and a dentry is
selected for expire but, since there is no lock held between the selection
and setting of the expiring flag, a process may find the flag clear and
continue walking into the mount tree at the same time the daemon attempts
the expire it.
Signed-off-by: Ian Kent <raven@themaw.net>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 61d1dca..1c2579d 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -133,7 +133,10 @@
/* Block on any pending expiry here; invalidate the dentry
when expiration is done to trigger mount request with a new
dentry */
- if (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
+ spin_lock(&sbi->fs_lock);
+ if (ino->flags & AUTOFS_INF_EXPIRING) {
+ spin_unlock(&sbi->fs_lock);
+
DPRINTK("waiting for expire %p name=%.*s",
dentry, dentry->d_name.len, dentry->d_name.name);
@@ -149,8 +152,11 @@
status = d_invalidate(dentry);
if (status != -EBUSY)
return -EAGAIN;
- }
+ goto cont;
+ }
+ spin_unlock(&sbi->fs_lock);
+cont:
DPRINTK("dentry=%p %.*s ino=%p",
dentry, dentry->d_name.len, dentry->d_name.name, dentry->d_inode);
@@ -229,15 +235,21 @@
goto done;
/* If an expire request is pending wait for it. */
- if (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
+ spin_lock(&sbi->fs_lock);
+ if (ino->flags & AUTOFS_INF_EXPIRING) {
+ spin_unlock(&sbi->fs_lock);
+
DPRINTK("waiting for active request %p name=%.*s",
dentry, dentry->d_name.len, dentry->d_name.name);
status = autofs4_wait(sbi, dentry, NFY_NONE);
DPRINTK("request done status=%d", status);
- }
+ goto cont;
+ }
+ spin_unlock(&sbi->fs_lock);
+cont:
/*
* If the dentry contains directories then it is an
* autofs multi-mount with no root mount offset. So
@@ -292,8 +304,11 @@
int status = 1;
/* Pending dentry */
+ spin_lock(&sbi->fs_lock);
if (autofs4_ispending(dentry)) {
/* The daemon never causes a mount to trigger */
+ spin_unlock(&sbi->fs_lock);
+
if (oz_mode)
return 1;
@@ -316,6 +331,7 @@
return status;
}
+ spin_unlock(&sbi->fs_lock);
/* Negative dentry.. invalidate if "old" */
if (dentry->d_inode == NULL)
@@ -329,6 +345,7 @@
DPRINTK("dentry=%p %.*s, emptydir",
dentry, dentry->d_name.len, dentry->d_name.name);
spin_unlock(&dcache_lock);
+
/* The daemon never causes a mount to trigger */
if (oz_mode)
return 1;
@@ -521,13 +538,18 @@
* so it must have been successful, so just wait for it.
*/
ino = autofs4_dentry_ino(expiring);
- while (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
+ spin_lock(&sbi->fs_lock);
+ if (ino->flags & AUTOFS_INF_EXPIRING) {
+ spin_unlock(&sbi->fs_lock);
DPRINTK("wait for incomplete expire %p name=%.*s",
expiring, expiring->d_name.len,
expiring->d_name.name);
autofs4_wait(sbi, expiring, NFY_NONE);
DPRINTK("request completed");
+ goto cont;
}
+ spin_unlock(&sbi->fs_lock);
+cont:
spin_lock(&sbi->lookup_lock);
if (!list_empty(&ino->expiring))
list_del_init(&ino->expiring);