| Message ID | 1375799403-28544-3-git-send-email-miklos@szeredi.hu (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Aug 06, 2013 at 04:30:01PM +0200, Miklos Szeredi wrote: > From: Miklos Szeredi <mszeredi@suse.cz> > > 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 after setting > DCACHE_MOUNTED on the soon-to-be mountpoint and with the rename seqlock > taken for write. This ensures that the only one of have_submounts() or > has_unlinked_ancestor() can succeed. > > Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> > --- > fs/dcache.c | 28 ++++++++++++++++++++++++++++ > fs/internal.h | 1 + > fs/namespace.c | 9 +++++++++ > 3 files changed, 38 insertions(+) > > diff --git a/fs/dcache.c b/fs/dcache.c > index ba429d9..eae7cc1 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -1103,6 +1103,34 @@ rename_retry: > } > EXPORT_SYMBOL(have_submounts); > > +static bool __has_unlinked_ancestor(struct dentry *dentry) > +{ > + struct dentry *this; > + > + for (this = dentry; !IS_ROOT(this); this = this->d_parent) { > + if (d_unhashed(this)) Actually we need to take ->d_lock around this d_unhashed() since the __d_drop() is done outside the read read_seqbegin/read_seqretry() region but with d_lock held. Thanks, Miklos > + return true; > + } > + return false; > +} > + > +/* > + * Called by mount code to check if the mountpoint is reachable (e.g. NFS can > + * unhash a directory dentry and then the complete subtree can become > + * unreachable). > + */ > +bool has_unlinked_ancestor(struct dentry *dentry) > +{ > + bool found; > + > + /* Need exclusion wrt. check_submounts_and_drop() */ > + write_seqlock(&rename_lock); > + found = __has_unlinked_ancestor(dentry); > + write_sequnlock(&rename_lock); > + > + return found; > +} > + > /* > * Search the dentry child list of the specified parent, > * and move any unused dentries to the end of the unused > diff --git a/fs/internal.h b/fs/internal.h > index 7c5f01c..d232355 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 bool has_unlinked_ancestor(struct dentry *dentry); > > /* > * read_write.c > diff --git a/fs/namespace.c b/fs/namespace.c > index 7b1ca9b..bb92a9c 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -634,6 +634,15 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry) > } > dentry->d_flags |= DCACHE_MOUNTED; > spin_unlock(&dentry->d_lock); > + > + if (has_unlinked_ancestor(dentry)) { > + spin_lock(&dentry->d_lock); > + dentry->d_flags &= ~DCACHE_MOUNTED; > + spin_unlock(&dentry->d_lock); > + kfree(mp); > + return ERR_PTR(-ENOENT); > + } > + > mp->m_dentry = dentry; > mp->m_count = 1; > list_add(&mp->m_hash, chain); > -- > 1.8.1.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/dcache.c b/fs/dcache.c index ba429d9..eae7cc1 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1103,6 +1103,34 @@ rename_retry: } EXPORT_SYMBOL(have_submounts); +static bool __has_unlinked_ancestor(struct dentry *dentry) +{ + struct dentry *this; + + for (this = dentry; !IS_ROOT(this); this = this->d_parent) { + if (d_unhashed(this)) + return true; + } + return false; +} + +/* + * Called by mount code to check if the mountpoint is reachable (e.g. NFS can + * unhash a directory dentry and then the complete subtree can become + * unreachable). + */ +bool has_unlinked_ancestor(struct dentry *dentry) +{ + bool found; + + /* Need exclusion wrt. check_submounts_and_drop() */ + write_seqlock(&rename_lock); + found = __has_unlinked_ancestor(dentry); + write_sequnlock(&rename_lock); + + return found; +} + /* * Search the dentry child list of the specified parent, * and move any unused dentries to the end of the unused diff --git a/fs/internal.h b/fs/internal.h index 7c5f01c..d232355 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 bool has_unlinked_ancestor(struct dentry *dentry); /* * read_write.c diff --git a/fs/namespace.c b/fs/namespace.c index 7b1ca9b..bb92a9c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -634,6 +634,15 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry) } dentry->d_flags |= DCACHE_MOUNTED; spin_unlock(&dentry->d_lock); + + if (has_unlinked_ancestor(dentry)) { + spin_lock(&dentry->d_lock); + dentry->d_flags &= ~DCACHE_MOUNTED; + spin_unlock(&dentry->d_lock); + kfree(mp); + return ERR_PTR(-ENOENT); + } + mp->m_dentry = dentry; mp->m_count = 1; list_add(&mp->m_hash, chain);