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/expire.c b/fs/autofs4/expire.c
index 894fee5..19f5bea 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -292,6 +292,8 @@
struct list_head *next;
int do_now = how & AUTOFS_EXP_IMMEDIATE;
int exp_leaves = how & AUTOFS_EXP_LEAVES;
+ struct autofs_info *ino;
+ unsigned int ino_count;
if (!root)
return NULL;
@@ -316,6 +318,9 @@
dentry = dget(dentry);
spin_unlock(&dcache_lock);
+ spin_lock(&sbi->fs_lock);
+ ino = autofs4_dentry_ino(dentry);
+
/*
* Case 1: (i) indirect mount or top level pseudo direct mount
* (autofs-4.1).
@@ -326,6 +331,11 @@
DPRINTK("checking mountpoint %p %.*s",
dentry, (int)dentry->d_name.len, dentry->d_name.name);
+ /* Path walk currently on this dentry? */
+ ino_count = atomic_read(&ino->count) + 2;
+ if (atomic_read(&dentry->d_count) > ino_count)
+ goto next;
+
/* Can we umount this guy */
if (autofs4_mount_busy(mnt, dentry))
goto next;
@@ -343,23 +353,25 @@
/* Case 2: tree mount, expire iff entire tree is not busy */
if (!exp_leaves) {
- /* Lock the tree as we must expire as a whole */
- spin_lock(&sbi->fs_lock);
- if (!autofs4_tree_busy(mnt, dentry, timeout, do_now)) {
- struct autofs_info *inf = autofs4_dentry_ino(dentry);
+ /* Path walk currently on this dentry? */
+ ino_count = atomic_read(&ino->count) + 1;
+ if (atomic_read(&dentry->d_count) > ino_count)
+ goto next;
- /* Set this flag early to catch sys_chdir and the like */
- inf->flags |= AUTOFS_INF_EXPIRING;
- spin_unlock(&sbi->fs_lock);
+ if (!autofs4_tree_busy(mnt, dentry, timeout, do_now)) {
expired = dentry;
goto found;
}
- spin_unlock(&sbi->fs_lock);
/*
* Case 3: pseudo direct mount, expire individual leaves
* (autofs-4.1).
*/
} else {
+ /* Path walk currently on this dentry? */
+ ino_count = atomic_read(&ino->count) + 1;
+ if (atomic_read(&dentry->d_count) > ino_count)
+ goto next;
+
expired = autofs4_check_leaves(mnt, dentry, timeout, do_now);
if (expired) {
dput(dentry);
@@ -367,6 +379,7 @@
}
}
next:
+ spin_unlock(&sbi->fs_lock);
dput(dentry);
spin_lock(&dcache_lock);
next = next->next;
@@ -377,6 +390,9 @@
found:
DPRINTK("returning %p %.*s",
expired, (int)expired->d_name.len, expired->d_name.name);
+ ino = autofs4_dentry_ino(expired);
+ ino->flags |= AUTOFS_INF_EXPIRING;
+ spin_unlock(&sbi->fs_lock);
spin_lock(&dcache_lock);
list_move(&expired->d_parent->d_subdirs, &expired->d_u.d_child);
spin_unlock(&dcache_lock);
@@ -390,7 +406,9 @@
struct autofs_packet_expire __user *pkt_p)
{
struct autofs_packet_expire pkt;
+ struct autofs_info *ino;
struct dentry *dentry;
+ int ret = 0;
memset(&pkt,0,sizeof pkt);
@@ -406,9 +424,14 @@
dput(dentry);
if ( copy_to_user(pkt_p, &pkt, sizeof(struct autofs_packet_expire)) )
- return -EFAULT;
+ ret = -EFAULT;
- return 0;
+ spin_lock(&sbi->fs_lock);
+ ino = autofs4_dentry_ino(dentry);
+ ino->flags &= ~AUTOFS_INF_EXPIRING;
+ spin_unlock(&sbi->fs_lock);
+
+ return ret;
}
/* Call repeatedly until it returns -EAGAIN, meaning there's nothing
@@ -433,9 +456,10 @@
/* This is synchronous because it makes the daemon a
little easier */
- ino->flags |= AUTOFS_INF_EXPIRING;
ret = autofs4_wait(sbi, dentry, NFY_EXPIRE);
+ spin_lock(&sbi->fs_lock);
ino->flags &= ~AUTOFS_INF_EXPIRING;
+ spin_unlock(&sbi->fs_lock);
dput(dentry);
}