6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Amir Goldstein [ Upstream commit 669bb5af15d41a21359d00a441490f87a88eb52a ] Daehyeon reported a race wherein fsnotify_removeinode() can be called when inode still has a live alias. This can lead to several undesired outcomes such as crashes in fsnotify code or avoidance of inode mark notifications. Check that inode is really "dead", meaning no nlink and no more aliases before calling fsnotify_inoderemove() for final cleanup of inode marks. Also do not allow open_by_handle() to add new aliases to a "dead" inode. Ideally, we'd call fsnotify_inoderemove() once last inode reference is dropped to make things simpler. Alas fsnotify inode marks currently hold inode references and thus this doesn't work. Once we teach fsnotify to avoid holding inode references, these games with dead inodes can go as well. Reported-and-tested-by: Daehyeon Ko <4ncienth@gmail.com> Closes: https://lore.kernel.org/linux-fsdevel/20260827045007.3831259-1-4ncienth@gmail.com/ CC: stable@vger.kernel.org Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/20260902164924.1333135-2-jack@suse.cz Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Sasha Levin --- fs/dcache.c | 27 ++++++++++++++++++++++++--- 1 file changed, 24 insertions(+), 3 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 5ee1c3d592c85..1b4c210338022 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -442,6 +442,17 @@ static void dentry_free(struct dentry *dentry) call_rcu(&dentry->d_u.d_rcu, __d_free); } +/* + * If inode is unlinked and doesn't have any aliases (i.e., all fds pointing to + * it are closed), it is pretty much dead. Except that file handle lookup could + * still revive it which causes issues to fsnotify. So once inode reaches this + * state we make sure to block creating any new aliases. + */ +static bool inode_notify_dead(struct inode *inode) +{ + return !inode->i_nlink && hlist_empty(&inode->i_dentry); +} + /* * Release the dentry's inode, using the filesystem * d_iput() operation if defined. @@ -451,14 +462,16 @@ static void dentry_unlink_inode(struct dentry * dentry) __releases(dentry->d_inode->i_lock) { struct inode *inode = dentry->d_inode; + bool notify_dead; raw_write_seqcount_begin(&dentry->d_seq); __d_clear_type_and_inode(dentry); hlist_del_init(&dentry->d_u.d_alias); raw_write_seqcount_end(&dentry->d_seq); + notify_dead = inode_notify_dead(inode); spin_unlock(&dentry->d_lock); spin_unlock(&inode->i_lock); - if (!inode->i_nlink) + if (notify_dead) fsnotify_inoderemove(inode); if (dentry->d_op && dentry->d_op->d_iput) dentry->d_op->d_iput(dentry, inode); @@ -2022,7 +2035,12 @@ static struct dentry *__d_obtain_alias(struct inode *inode, bool disconnected) sb = inode->i_sb; - res = d_find_any_alias(inode); /* existing alias? */ + spin_lock(&inode->i_lock); + if (!inode_notify_dead(inode)) + res = __d_find_any_alias(inode); /* existing alias? */ + else + res = ERR_PTR(-ESTALE); + spin_unlock(&inode->i_lock); if (res) goto out; @@ -2034,7 +2052,10 @@ static struct dentry *__d_obtain_alias(struct inode *inode, bool disconnected) security_d_instantiate(new, inode); spin_lock(&inode->i_lock); - res = __d_find_any_alias(inode); /* recheck under lock */ + if (!inode_notify_dead(inode)) + res = __d_find_any_alias(inode); /* recheck under lock */ + else + res = ERR_PTR(-ESTALE); if (likely(!res)) { /* still no alias, attach a disconnected dentry */ unsigned add_flags = d_flags_for_inode(inode); -- 2.53.0