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author | Miklos Szeredi <miklos@szeredi.hu> | 2013-09-05 14:39:11 +0200 |
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committer | Al Viro <viro@zeniv.linux.org.uk> | 2013-09-05 16:23:50 -0400 |
commit | eed810076685c77dc9a8c5c3593e641c93caed1c (patch) | |
tree | 5aba507073b0a7e29dfa0739272dfeda16eb5e29 /fs/dcache.c | |
parent | 848ac114e847af3f1f9141c90a39ebe79bdb13b3 (diff) | |
download | op-kernel-dev-eed810076685c77dc9a8c5c3593e641c93caed1c.zip op-kernel-dev-eed810076685c77dc9a8c5c3593e641c93caed1c.tar.gz |
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/dcache.c')
-rw-r--r-- | fs/dcache.c | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index ce5a7e6..761e31b 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 |