From b97ac51f8492db592a4eccfadd8808e8b09ef0ad Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Thu, 1 Jun 2023 12:58:24 +0200 Subject: [PATCH] fs: Establish locking order for unrelated directories commit f23ce757185319886ca80c4864ce5f81ac6cc9e9 upstream. Currently the locking order of inode locks for directories that are not in ancestor relationship is not defined because all operations that needed to lock two directories like this were serialized by sb->s_vfs_rename_mutex. However some filesystems need to lock two subdirectories for RENAME_EXCHANGE operations and for this we need the locking order established even for two tree-unrelated directories. Provide a helper function lock_two_inodes() that establishes lock ordering for any two inodes and use it in lock_two_directories(). CC: stable@vger.kernel.org Signed-off-by: Jan Kara Message-Id: <20230601105830.13168-4-jack@suse.cz> Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman --- fs/inode.c | 42 ++++++++++++++++++++++++++++++++++++++++++ fs/internal.h | 2 ++ fs/namei.c | 4 ++-- 3 files changed, 46 insertions(+), 2 deletions(-) diff --git a/fs/inode.c b/fs/inode.c index 140a62e5382c..f7c8c0fe11d4 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -1012,6 +1012,48 @@ void discard_new_inode(struct inode *inode) } EXPORT_SYMBOL(discard_new_inode); +/** + * lock_two_inodes - lock two inodes (may be regular files but also dirs) + * + * Lock any non-NULL argument. The caller must make sure that if he is passing + * in two directories, one is not ancestor of the other. Zero, one or two + * objects may be locked by this function. + * + * @inode1: first inode to lock + * @inode2: second inode to lock + * @subclass1: inode lock subclass for the first lock obtained + * @subclass2: inode lock subclass for the second lock obtained + */ +void lock_two_inodes(struct inode *inode1, struct inode *inode2, + unsigned subclass1, unsigned subclass2) +{ + if (!inode1 || !inode2) { + /* + * Make sure @subclass1 will be used for the acquired lock. + * This is not strictly necessary (no current caller cares) but + * let's keep things consistent. + */ + if (!inode1) + swap(inode1, inode2); + goto lock; + } + + /* + * If one object is directory and the other is not, we must make sure + * to lock directory first as the other object may be its child. + */ + if (S_ISDIR(inode2->i_mode) == S_ISDIR(inode1->i_mode)) { + if (inode1 > inode2) + swap(inode1, inode2); + } else if (!S_ISDIR(inode1->i_mode)) + swap(inode1, inode2); +lock: + if (inode1) + inode_lock_nested(inode1, subclass1); + if (inode2 && inode2 != inode1) + inode_lock_nested(inode2, subclass2); +} + /** * lock_two_nondirectories - take two i_mutexes on non-directory objects * diff --git a/fs/internal.h b/fs/internal.h index 61aed95f83d1..377f984e9226 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -138,6 +138,8 @@ extern int vfs_open(const struct path *, struct file *); extern long prune_icache_sb(struct super_block *sb, struct shrink_control *sc); extern void inode_add_lru(struct inode *inode); extern int dentry_needs_remove_privs(struct dentry *dentry); +void lock_two_inodes(struct inode *inode1, struct inode *inode2, + unsigned subclass1, unsigned subclass2); /* * fs-writeback.c diff --git a/fs/namei.c b/fs/namei.c index d220df830c49..260a1012be06 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2870,8 +2870,8 @@ struct dentry *lock_rename(struct dentry *p1, struct dentry *p2) return p; } - inode_lock_nested(p1->d_inode, I_MUTEX_PARENT); - inode_lock_nested(p2->d_inode, I_MUTEX_PARENT2); + lock_two_inodes(p1->d_inode, p2->d_inode, + I_MUTEX_PARENT, I_MUTEX_PARENT2); return NULL; } EXPORT_SYMBOL(lock_rename);