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-rw-r--r--fs/inotify.c150
-rw-r--r--include/linux/inotify.h11
-rw-r--r--kernel/audit_tree.c91
-rw-r--r--kernel/auditfilter.c14
4 files changed, 218 insertions, 48 deletions
diff --git a/fs/inotify.c b/fs/inotify.c
index 690e72595e6..7bbed1b8982 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 bd578578a8b..37ea2894b3c 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 8ba0e0d934f..8b509441f49 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 b7d354e2b0e..9fd85a4640a 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);
}
}
}
generated by cgit (git 2.34.1) at 2024-11-15 15:18:57 +0000