From: "Steven Rostedt (Google)" <rost...@goodmis.org> The eventfs_inode (ei) is protected by SRCU, but the ei->dentry is not. It is protected by the eventfs_mutex. Anytime the eventfs_mutex is released, and access to the ei->dentry needs to be done, it should first check if ei->is_freed is set under the eventfs_mutex. If it is, then the ei->dentry is invalid and must not be used. The ei->dentry must only be accessed under the eventfs_mutex and after checking if ei->is_freed is set.
When the ei is being freed, it will (under the eventfs_mutex) set is_freed and at the same time move the dentry to a free list to be cleared after the eventfs_mutex is released. This means that any access to the ei->dentry must check first if ei->is_freed is set, because if it is, then the dentry is on its way to be freed. Also add comments to describe this better. Link: https://lore.kernel.org/all/CA+G9fYt6pY+tMZEOg=soeywqoe19fgp3ur15sgowkdk+_x8...@mail.gmail.com/ Link: https://lore.kernel.org/all/CA+G9fYuDP3hVQ3t7FfrBAjd_WFVSurMgCepTxunSJf=MTe=6...@mail.gmail.com/ Fixes: 5790b1fb3d672 ("eventfs: Remove eventfs_file and just use eventfs_inode") Reported-by: Linux Kernel Functional Testing <l...@linaro.org> Reported-by: Naresh Kamboju <naresh.kamb...@linaro.org> Reported-by: Beau Belgrave <be...@linux.microsoft.com> Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org> --- Changes since v1: https://lore.kernel.org/all/20231028163749.0d342...@rorschach.local.home/ - Add comment about ei->is_freed is a union along with ei->rcu and ei->del_list so that others can find where ei->is_freed is set and not get confused about why ei->dentry is being removed but ei->is_freed isn't mentioned. - And fixed change log to remove the double "Reported-by". fs/tracefs/event_inode.c | 65 +++++++++++++++++++++++++++++++++------- fs/tracefs/internal.h | 3 +- 2 files changed, 56 insertions(+), 12 deletions(-) diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 4d2da7480e5f..45bddce7c747 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -24,7 +24,20 @@ #include <linux/delay.h> #include "internal.h" +/* + * eventfs_mutex protects the eventfs_inode (ei) dentry. Any access + * to the ei->dentry must be done under this mutex and after checking + * if ei->is_freed is not set. The ei->dentry is released under the + * mutex at the same time ei->is_freed is set. If ei->is_freed is set + * then the ei->dentry is invalid. + */ static DEFINE_MUTEX(eventfs_mutex); + +/* + * The eventfs_inode (ei) itself is protected by SRCU. It is released from + * its parent's list and will have is_freed set (under eventfs_mutex). + * After the SRCU grace period is over, the ei may be freed. + */ DEFINE_STATIC_SRCU(eventfs_srcu); static struct dentry *eventfs_root_lookup(struct inode *dir, @@ -234,6 +247,10 @@ create_file_dentry(struct eventfs_inode *ei, struct dentry **e_dentry, bool invalidate = false; mutex_lock(&eventfs_mutex); + if (ei->is_freed) { + mutex_unlock(&eventfs_mutex); + return NULL; + } /* If the e_dentry already has a dentry, use it */ if (*e_dentry) { /* lookup does not need to up the ref count */ @@ -307,6 +324,8 @@ static void eventfs_post_create_dir(struct eventfs_inode *ei) struct eventfs_inode *ei_child; struct tracefs_inode *ti; + lockdep_assert_held(&eventfs_mutex); + /* srcu lock already held */ /* fill parent-child relation */ list_for_each_entry_srcu(ei_child, &ei->children, list, @@ -320,6 +339,7 @@ static void eventfs_post_create_dir(struct eventfs_inode *ei) /** * create_dir_dentry - Create a directory dentry for the eventfs_inode + * @pei: The eventfs_inode parent of ei. * @ei: The eventfs_inode to create the directory for * @parent: The dentry of the parent of this directory * @lookup: True if this is called by the lookup code @@ -327,12 +347,17 @@ static void eventfs_post_create_dir(struct eventfs_inode *ei) * This creates and attaches a directory dentry to the eventfs_inode @ei. */ static struct dentry * -create_dir_dentry(struct eventfs_inode *ei, struct dentry *parent, bool lookup) +create_dir_dentry(struct eventfs_inode *pei, struct eventfs_inode *ei, + struct dentry *parent, bool lookup) { bool invalidate = false; struct dentry *dentry = NULL; mutex_lock(&eventfs_mutex); + if (pei->is_freed || ei->is_freed) { + mutex_unlock(&eventfs_mutex); + return NULL; + } if (ei->dentry) { /* If the dentry already has a dentry, use it */ dentry = ei->dentry; @@ -435,7 +460,7 @@ static struct dentry *eventfs_root_lookup(struct inode *dir, */ mutex_lock(&eventfs_mutex); ei = READ_ONCE(ti->private); - if (ei) + if (ei && !ei->is_freed) ei_dentry = READ_ONCE(ei->dentry); mutex_unlock(&eventfs_mutex); @@ -449,7 +474,7 @@ static struct dentry *eventfs_root_lookup(struct inode *dir, if (strcmp(ei_child->name, name) != 0) continue; ret = simple_lookup(dir, dentry, flags); - create_dir_dentry(ei_child, ei_dentry, true); + create_dir_dentry(ei, ei_child, ei_dentry, true); created = true; break; } @@ -583,7 +608,7 @@ static int dcache_dir_open_wrapper(struct inode *inode, struct file *file) list_for_each_entry_srcu(ei_child, &ei->children, list, srcu_read_lock_held(&eventfs_srcu)) { - d = create_dir_dentry(ei_child, parent, false); + d = create_dir_dentry(ei, ei_child, parent, false); if (d) { ret = add_dentries(&dentries, d, cnt); if (ret < 0) @@ -637,6 +662,13 @@ static int dcache_readdir_wrapper(struct file *file, struct dir_context *ctx) return ret; } +static void free_ei(struct eventfs_inode *ei) +{ + kfree_const(ei->name); + kfree(ei->d_children); + kfree(ei); +} + /** * eventfs_create_dir - Create the eventfs_inode for this directory * @name: The name of the directory to create. @@ -700,12 +732,20 @@ struct eventfs_inode *eventfs_create_dir(const char *name, struct eventfs_inode ei->nr_entries = size; ei->data = data; INIT_LIST_HEAD(&ei->children); + INIT_LIST_HEAD(&ei->list); mutex_lock(&eventfs_mutex); - list_add_tail(&ei->list, &parent->children); - ei->d_parent = parent->dentry; + if (!parent->is_freed) { + list_add_tail(&ei->list, &parent->children); + ei->d_parent = parent->dentry; + } mutex_unlock(&eventfs_mutex); + /* Was the parent freed? */ + if (list_empty(&ei->list)) { + free_ei(ei); + ei = NULL; + } return ei; } @@ -787,13 +827,11 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry return ERR_PTR(-ENOMEM); } -static void free_ei(struct rcu_head *head) +static void free_rcu_ei(struct rcu_head *head) { struct eventfs_inode *ei = container_of(head, struct eventfs_inode, rcu); - kfree_const(ei->name); - kfree(ei->d_children); - kfree(ei); + free_ei(ei); } /** @@ -880,7 +918,12 @@ void eventfs_remove_dir(struct eventfs_inode *ei) for (i = 0; i < ei->nr_entries; i++) unhook_dentry(&ei->d_children[i], &dentry_list); unhook_dentry(&ei->dentry, &dentry_list); - call_srcu(&eventfs_srcu, &ei->rcu, free_ei); + /* + * Note, ei->is_freed is a union along with ei->rcu + * and ei->del_list. When the ei is added to either + * of those lists, it automatically sets ei->is_freed. + */ + call_srcu(&eventfs_srcu, &ei->rcu, free_rcu_ei); } mutex_unlock(&eventfs_mutex); diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h index 64fde9490f52..21a1fa682b74 100644 --- a/fs/tracefs/internal.h +++ b/fs/tracefs/internal.h @@ -30,7 +30,7 @@ struct eventfs_inode { const struct eventfs_entry *entries; const char *name; struct list_head children; - struct dentry *dentry; + struct dentry *dentry; /* Check is_freed to access */ struct dentry *d_parent; struct dentry **d_children; void *data; @@ -39,6 +39,7 @@ struct eventfs_inode { * @del_list: list of eventfs_inode to delete * @rcu: eventfs_inode to delete in RCU * @is_freed: node is freed if one of the above is set + * Note if is_freed is set, then dentry is corrupted. */ union { struct list_head del_list; -- 2.42.0
