diff options
| -rw-r--r-- | fs/inotify.c | 150 | ||||
| -rw-r--r-- | include/linux/inotify.h | 11 | ||||
| -rw-r--r-- | kernel/audit_tree.c | 91 | ||||
| -rw-r--r-- | kernel/auditfilter.c | 14 |
4 files changed, 218 insertions, 48 deletions
diff --git a/fs/inotify.c b/fs/inotify.c index 690e725..7bbed1b 100644 --- a/fs/inotify.c +++ b/fs/inotify.c @@ -106,6 +106,20 @@ void get_inotify_watch(struct inotify_watch *watch) } EXPORT_SYMBOL_GPL(get_inotify_watch); +int pin_inotify_watch(struct inotify_watch *watch) +{ + struct super_block *sb = watch->inode->i_sb; + spin_lock(&sb_lock); + if (sb->s_count >= S_BIAS) { + atomic_inc(&sb->s_active); + spin_unlock(&sb_lock); + atomic_inc(&watch->count); + return 1; + } + spin_unlock(&sb_lock); + return 0; +} + /** * put_inotify_watch - decrements the ref count on a given watch. cleans up * watch references if the count reaches zero. inotify_watch is freed by @@ -124,6 +138,13 @@ void put_inotify_watch(struct inotify_watch *watch) } EXPORT_SYMBOL_GPL(put_inotify_watch); +void unpin_inotify_watch(struct inotify_watch *watch) +{ + struct super_block *sb = watch->inode->i_sb; + put_inotify_watch(watch); + deactivate_super(sb); +} + /* * inotify_handle_get_wd - returns the next WD for use by the given handle * @@ -479,6 +500,112 @@ void inotify_init_watch(struct inotify_watch *watch) } EXPORT_SYMBOL_GPL(inotify_init_watch); +/* + * Watch removals suck violently. To kick the watch out we need (in this + * order) inode->inotify_mutex and ih->mutex. That's fine if we have + * a hold on inode; however, for all other cases we need to make damn sure + * we don't race with umount. We can *NOT* just grab a reference to a + * watch - inotify_unmount_inodes() will happily sail past it and we'll end + * with reference to inode potentially outliving its superblock. Ideally + * we just want to grab an active reference to superblock if we can; that + * will make sure we won't go into inotify_umount_inodes() until we are + * done. Cleanup is just deactivate_super(). However, that leaves a messy + * case - what if we *are* racing with umount() and active references to + * superblock can't be acquired anymore? We can bump ->s_count, grab + * ->s_umount, which will almost certainly wait until the superblock is shut + * down and the watch in question is pining for fjords. That's fine, but + * there is a problem - we might have hit the window between ->s_active + * getting to 0 / ->s_count - below S_BIAS (i.e. the moment when superblock + * is past the point of no return and is heading for shutdown) and the + * moment when deactivate_super() acquires ->s_umount. We could just do + * drop_super() yield() and retry, but that's rather antisocial and this + * stuff is luser-triggerable. OTOH, having grabbed ->s_umount and having + * found that we'd got there first (i.e. that ->s_root is non-NULL) we know + * that we won't race with inotify_umount_inodes(). So we could grab a + * reference to watch and do the rest as above, just with drop_super() instead + * of deactivate_super(), right? Wrong. We had to drop ih->mutex before we + * could grab ->s_umount. So the watch could've been gone already. + * + * That still can be dealt with - we need to save watch->wd, do idr_find() + * and compare its result with our pointer. If they match, we either have + * the damn thing still alive or we'd lost not one but two races at once, + * the watch had been killed and a new one got created with the same ->wd + * at the same address. That couldn't have happened in inotify_destroy(), + * but inotify_rm_wd() could run into that. Still, "new one got created" + * is not a problem - we have every right to kill it or leave it alone, + * whatever's more convenient. + * + * So we can use idr_find(...) == watch && watch->inode->i_sb == sb as + * "grab it and kill it" check. If it's been our original watch, we are + * fine, if it's a newcomer - nevermind, just pretend that we'd won the + * race and kill the fscker anyway; we are safe since we know that its + * superblock won't be going away. + * + * And yes, this is far beyond mere "not very pretty"; so's the entire + * concept of inotify to start with. + */ + +/** + * pin_to_kill - pin the watch down for removal + * @ih: inotify handle + * @watch: watch to kill + * + * Called with ih->mutex held, drops it. Possible return values: + * 0 - nothing to do, it has died + * 1 - remove it, drop the reference and deactivate_super() + * 2 - remove it, drop the reference and drop_super(); we tried hard to avoid + * that variant, since it involved a lot of PITA, but that's the best that + * could've been done. + */ +static int pin_to_kill(struct inotify_handle *ih, struct inotify_watch *watch) +{ + struct super_block *sb = watch->inode->i_sb; + s32 wd = watch->wd; + + spin_lock(&sb_lock); + if (sb->s_count >= S_BIAS) { + atomic_inc(&sb->s_active); + spin_unlock(&sb_lock); + get_inotify_watch(watch); + mutex_unlock(&ih->mutex); + return 1; /* the best outcome */ + } + sb->s_count++; + spin_unlock(&sb_lock); + mutex_unlock(&ih->mutex); /* can't grab ->s_umount under it */ + down_read(&sb->s_umount); + if (likely(!sb->s_root)) { + /* fs is already shut down; the watch is dead */ + drop_super(sb); + return 0; + } + /* raced with the final deactivate_super() */ + mutex_lock(&ih->mutex); + if (idr_find(&ih->idr, wd) != watch || watch->inode->i_sb != sb) { + /* the watch is dead */ + mutex_unlock(&ih->mutex); + drop_super(sb); + return 0; + } + /* still alive or freed and reused with the same sb and wd; kill */ + get_inotify_watch(watch); + mutex_unlock(&ih->mutex); + return 2; +} + +static void unpin_and_kill(struct inotify_watch *watch, int how) +{ + struct super_block *sb = watch->inode->i_sb; + put_inotify_watch(watch); + switch (how) { + case 1: + deactivate_super(sb); + break; + case 2: + drop_super(sb); + } +} + /** * inotify_destroy - clean up and destroy an inotify instance * @ih: inotify handle @@ -490,11 +617,15 @@ void inotify_destroy(struct inotify_handle *ih) * pretty. We cannot do a simple iteration over the list, because we * do not know the inode until we iterate to the watch. But we need to * hold inode->inotify_mutex before ih->mutex. The following works. + * + * AV: it had to become even uglier to start working ;-/ */ while (1) { struct inotify_watch *watch; struct list_head *watches; + struct super_block *sb; struct inode *inode; + int how; mutex_lock(&ih->mutex); watches = &ih->watches; @@ -503,8 +634,10 @@ void inotify_destroy(struct inotify_handle *ih) break; } watch = list_first_entry(watches, struct inotify_watch, h_list); - get_inotify_watch(watch); - mutex_unlock(&ih->mutex); + sb = watch->inode->i_sb; + how = pin_to_kill(ih, watch); + if (!how) + continue; inode = watch->inode; mutex_lock(&inode->inotify_mutex); @@ -518,7 +651,7 @@ void inotify_destroy(struct inotify_handle *ih) mutex_unlock(&ih->mutex); mutex_unlock(&inode->inotify_mutex); - put_inotify_watch(watch); + unpin_and_kill(watch, how); } /* free this handle: the put matching the get in inotify_init() */ @@ -719,7 +852,9 @@ void inotify_evict_watch(struct inotify_watch *watch) int inotify_rm_wd(struct inotify_handle *ih, u32 wd) { struct inotify_watch *watch; + struct super_block *sb; struct inode *inode; + int how; mutex_lock(&ih->mutex); watch = idr_find(&ih->idr, wd); @@ -727,9 +862,12 @@ int inotify_rm_wd(struct inotify_handle *ih, u32 wd) mutex_unlock(&ih->mutex); return -EINVAL; } - get_inotify_watch(watch); + sb = watch->inode->i_sb; + how = pin_to_kill(ih, watch); + if (!how) + return 0; + inode = watch->inode; - mutex_unlock(&ih->mutex); mutex_lock(&inode->inotify_mutex); mutex_lock(&ih->mutex); @@ -740,7 +878,7 @@ int inotify_rm_wd(struct inotify_handle *ih, u32 wd) mutex_unlock(&ih->mutex); mutex_unlock(&inode->inotify_mutex); - put_inotify_watch(watch); + unpin_and_kill(watch, how); return 0; } diff --git a/include/linux/inotify.h b/include/linux/inotify.h index bd57857..37ea289 100644 --- a/include/linux/inotify.h +++ b/include/linux/inotify.h @@ -134,6 +134,8 @@ extern void inotify_remove_watch_locked(struct inotify_handle *, struct inotify_watch *); extern void get_inotify_watch(struct inotify_watch *); extern void put_inotify_watch(struct inotify_watch *); +extern int pin_inotify_watch(struct inotify_watch *); +extern void unpin_inotify_watch(struct inotify_watch *); #else @@ -228,6 +230,15 @@ static inline void put_inotify_watch(struct inotify_watch *watch) { } +extern inline int pin_inotify_watch(struct inotify_watch *watch) +{ + return 0; +} + +extern inline void unpin_inotify_watch(struct inotify_watch *watch) +{ +} + #endif /* CONFIG_INOTIFY */ #endif /* __KERNEL __ */ diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c index 8ba0e0d..8b50944 100644 --- a/kernel/audit_tree.c +++ b/kernel/audit_tree.c @@ -24,6 +24,7 @@ struct audit_chunk { struct list_head trees; /* with root here */ int dead; int count; + atomic_long_t refs; struct rcu_head head; struct node { struct list_head list; @@ -56,7 +57,8 @@ static LIST_HEAD(prune_list); * tree is refcounted; one reference for "some rules on rules_list refer to * it", one for each chunk with pointer to it. * - * chunk is refcounted by embedded inotify_watch. + * chunk is refcounted by embedded inotify_watch + .refs (non-zero refcount + * of watch contributes 1 to .refs). * * node.index allows to get from node.list to containing chunk. * MSB of that sucker is stolen to mark taggings that we might have to @@ -121,6 +123,7 @@ static struct audit_chunk *alloc_chunk(int count) INIT_LIST_HEAD(&chunk->hash); INIT_LIST_HEAD(&chunk->trees); chunk->count = count; + atomic_long_set(&chunk->refs, 1); for (i = 0; i < count; i++) { INIT_LIST_HEAD(&chunk->owners[i].list); chunk->owners[i].index = i; @@ -129,9 +132,8 @@ static struct audit_chunk *alloc_chunk(int count) return chunk; } -static void __free_chunk(struct rcu_head *rcu) +static void free_chunk(struct audit_chunk *chunk) { - struct audit_chunk *chunk = container_of(rcu, struct audit_chunk, head); int i; for (i = 0; i < chunk->count; i++) { @@ -141,14 +143,16 @@ static void __free_chunk(struct rcu_head *rcu) kfree(chunk); } -static inline void free_chunk(struct audit_chunk *chunk) +void audit_put_chunk(struct audit_chunk *chunk) { - call_rcu(&chunk->head, __free_chunk); + if (atomic_long_dec_and_test(&chunk->refs)) + free_chunk(chunk); } -void audit_put_chunk(struct audit_chunk *chunk) +static void __put_chunk(struct rcu_head *rcu) { - put_inotify_watch(&chunk->watch); + struct audit_chunk *chunk = container_of(rcu, struct audit_chunk, head); + audit_put_chunk(chunk); } enum {HASH_SIZE = 128}; @@ -176,7 +180,7 @@ struct audit_chunk *audit_tree_lookup(const struct inode *inode) list_for_each_entry_rcu(p, list, hash) { if (p->watch.inode == inode) { - get_inotify_watch(&p->watch); + atomic_long_inc(&p->refs); return p; } } @@ -194,17 +198,49 @@ int audit_tree_match(struct audit_chunk *chunk, struct audit_tree *tree) /* tagging and untagging inodes with trees */ -static void untag_chunk(struct audit_chunk *chunk, struct node *p) +static struct audit_chunk *find_chunk(struct node *p) +{ + int index = p->index & ~(1U<<31); + p -= index; + return container_of(p, struct audit_chunk, owners[0]); +} + +static void untag_chunk(struct node *p) { + struct audit_chunk *chunk = find_chunk(p); struct audit_chunk *new; struct audit_tree *owner; int size = chunk->count - 1; int i, j; + if (!pin_inotify_watch(&chunk->watch)) { + /* + * Filesystem is shutting down; all watches are getting + * evicted, just take it off the node list for this + * tree and let the eviction logics take care of the + * rest. + */ + owner = p->owner; + if (owner->root == chunk) { + list_del_init(&owner->same_root); + owner->root = NULL; + } + list_del_init(&p->list); + p->owner = NULL; + put_tree(owner); + return; + } + + spin_unlock(&hash_lock); + + /* + * pin_inotify_watch() succeeded, so the watch won't go away + * from under us. + */ mutex_lock(&chunk->watch.inode->inotify_mutex); if (chunk->dead) { mutex_unlock(&chunk->watch.inode->inotify_mutex); - return; + goto out; } owner = p->owner; @@ -221,7 +257,7 @@ static void untag_chunk(struct audit_chunk *chunk, struct node *p) inotify_evict_watch(&chunk->watch); mutex_unlock(&chunk->watch.inode->inotify_mutex); put_inotify_watch(&chunk->watch); - return; + goto out; } new = alloc_chunk(size); @@ -263,7 +299,7 @@ static void untag_chunk(struct audit_chunk *chunk, struct node *p) inotify_evict_watch(&chunk->watch); mutex_unlock(&chunk->watch.inode->inotify_mutex); put_inotify_watch(&chunk->watch); - return; + goto out; Fallback: // do the best we can @@ -277,6 +313,9 @@ Fallback: put_tree(owner); spin_unlock(&hash_lock); mutex_unlock(&chunk->watch.inode->inotify_mutex); +out: + unpin_inotify_watch(&chunk->watch); + spin_lock(&hash_lock); } static int create_chunk(struct inode *inode, struct audit_tree *tree) @@ -387,13 +426,6 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree) return 0; } -static struct audit_chunk *find_chunk(struct node *p) -{ - int index = p->index & ~(1U<<31); - p -= index; - return container_of(p, struct audit_chunk, owners[0]); -} - static void kill_rules(struct audit_tree *tree) { struct audit_krule *rule, *next; @@ -431,17 +463,10 @@ static void prune_one(struct audit_tree *victim) spin_lock(&hash_lock); while (!list_empty(&victim->chunks)) { struct node *p; - struct audit_chunk *chunk; p = list_entry(victim->chunks.next, struct node, list); - chunk = find_chunk(p); - get_inotify_watch(&chunk->watch); - spin_unlock(&hash_lock); - - untag_chunk(chunk, p); - put_inotify_watch(&chunk->watch); - spin_lock(&hash_lock); + untag_chunk(p); } spin_unlock(&hash_lock); put_tree(victim); @@ -469,7 +494,6 @@ static void trim_marked(struct audit_tree *tree) while (!list_empty(&tree->chunks)) { struct node *node; - struct audit_chunk *chunk; node = list_entry(tree->chunks.next, struct node, list); @@ -477,14 +501,7 @@ static void trim_marked(struct audit_tree *tree) if (!(node->index & (1U<<31))) break; - chunk = find_chunk(node); - get_inotify_watch(&chunk->watch); - spin_unlock(&hash_lock); - - untag_chunk(chunk, node); - - put_inotify_watch(&chunk->watch); - spin_lock(&hash_lock); + untag_chunk(node); } if (!tree->root && !tree->goner) { tree->goner = 1; @@ -878,7 +895,7 @@ static void handle_event(struct inotify_watch *watch, u32 wd, u32 mask, static void destroy_watch(struct inotify_watch *watch) { struct audit_chunk *chunk = container_of(watch, struct audit_chunk, watch); - free_chunk(chunk); + call_rcu(&chunk->head, __put_chunk); } static const struct inotify_operations rtree_inotify_ops = { diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c index b7d354e..9fd85a4 100644 --- a/kernel/auditfilter.c +++ b/kernel/auditfilter.c @@ -1094,8 +1094,8 @@ static void audit_inotify_unregister(struct list_head *in_list) list_for_each_entry_safe(p, n, in_list, ilist) { list_del(&p->ilist); inotify_rm_watch(audit_ih, &p->wdata); - /* the put matching the get in audit_do_del_rule() */ - put_inotify_watch(&p->wdata); + /* the unpin matching the pin in audit_do_del_rule() */ + unpin_inotify_watch(&p->wdata); } } @@ -1389,9 +1389,13 @@ static inline int audit_del_rule(struct audit_entry *entry, /* Put parent on the inotify un-registration * list. Grab a reference before releasing * audit_filter_mutex, to be released in - * audit_inotify_unregister(). */ - list_add(&parent->ilist, &inotify_list); - get_inotify_watch(&parent->wdata); + * audit_inotify_unregister(). + * If filesystem is going away, just leave + * the sucker alone, eviction will take + * care of it. + */ + if (pin_inotify_watch(&parent->wdata)) + list_add(&parent->ilist, &inotify_list); } } } |
