diff options
| author | Miklos Szeredi <miklos@szeredi.hu> | 2013-09-05 14:39:11 +0200 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2013-09-05 16:23:50 -0400 |
| commit | eed810076685c77dc9a8c5c3593e641c93caed1c (patch) | |
| tree | 5aba507073b0a7e29dfa0739272dfeda16eb5e29 /fs | |
| parent | 848ac114e847af3f1f9141c90a39ebe79bdb13b3 (diff) | |
vfs: check unlinked ancestors before mount
We check submounts before doing d_drop() on a non-empty directory dentry in
NFS (have_submounts()), but we do not exclude a racing mount. Nor do we
prevent mounts to be added to the disconnected subtree using relative paths
after the d_drop().
This patch fixes these issues by checking for unlinked (unhashed, non-root)
ancestors before proceeding with the mount. This is done with rename
seqlock taken for write and with ->d_lock grabbed on each ancestor in turn,
including our dentry itself. This ensures that the only one of
check_submounts_and_drop() or has_unlinked_ancestor() can succeed.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/dcache.c | 33 | ||||
| -rw-r--r-- | fs/internal.h | 1 | ||||
| -rw-r--r-- | fs/namespace.c | 11 |
3 files changed, 39 insertions, 6 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index ce5a7e6d84cd..761e31bacbc2 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1184,6 +1184,39 @@ int have_submounts(struct dentry *parent) EXPORT_SYMBOL(have_submounts); /* + * Called by mount code to set a mountpoint and check if the mountpoint is + * reachable (e.g. NFS can unhash a directory dentry and then the complete + * subtree can become unreachable). + * + * Only one of check_submounts_and_drop() and d_set_mounted() must succeed. For + * this reason take rename_lock and d_lock on dentry and ancestors. + */ +int d_set_mounted(struct dentry *dentry) +{ + struct dentry *p; + int ret = -ENOENT; + write_seqlock(&rename_lock); + for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) { + /* Need exclusion wrt. check_submounts_and_drop() */ + spin_lock(&p->d_lock); + if (unlikely(d_unhashed(p))) { + spin_unlock(&p->d_lock); + goto out; + } + spin_unlock(&p->d_lock); + } + spin_lock(&dentry->d_lock); + if (!d_unlinked(dentry)) { + dentry->d_flags |= DCACHE_MOUNTED; + ret = 0; + } + spin_unlock(&dentry->d_lock); +out: + write_sequnlock(&rename_lock); + return ret; +} + +/* * Search the dentry child list of the specified parent, * and move any unused dentries to the end of the unused * list for prune_dcache(). We descend to the next level diff --git a/fs/internal.h b/fs/internal.h index 7c5f01cf619d..d20893795526 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -126,6 +126,7 @@ extern int invalidate_inodes(struct super_block *, bool); * dcache.c */ extern struct dentry *__d_alloc(struct super_block *, const struct qstr *); +extern int d_set_mounted(struct dentry *dentry); /* * read_write.c diff --git a/fs/namespace.c b/fs/namespace.c index ad8ea9bc2518..5997887cc64a 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -611,6 +611,7 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry) { struct list_head *chain = mountpoint_hashtable + hash(NULL, dentry); struct mountpoint *mp; + int ret; list_for_each_entry(mp, chain, m_hash) { if (mp->m_dentry == dentry) { @@ -626,14 +627,12 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry) if (!mp) return ERR_PTR(-ENOMEM); - spin_lock(&dentry->d_lock); - if (d_unlinked(dentry)) { - spin_unlock(&dentry->d_lock); + ret = d_set_mounted(dentry); + if (ret) { kfree(mp); - return ERR_PTR(-ENOENT); + return ERR_PTR(ret); } - dentry->d_flags |= DCACHE_MOUNTED; - spin_unlock(&dentry->d_lock); + mp->m_dentry = dentry; mp->m_count = 1; list_add(&mp->m_hash, chain); |