[PATCH 02/14] audit: Fix possible spurious -ENOSPC error

Jan Kara
2018-10-17T10:14:53Z

When an inode is tagged with a tree, tag_chunk() checks whether there is
audit_tree_group mark attached to the inode and adds one if not. However
nothing protects another tag_chunk() to add the mark between we've
checked and try to add the fsnotify mark thus resulting in an error from
fsnotify_add_mark() and consequently an ENOSPC error from tag_chunk().

Fix the problem by holding mark_mutex over the whole check-insert code
sequence.

Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
kernel/audit_tree.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
index 1b55b1026a36..8a74b468b666 100644
--- a/kernel/audit_tree.c
+++ b/kernel/audit_tree.c
@@ -342,25 +342,29 @@ static void untag_chunk(struct node *p)
spin_lock(&hash_lock);
}

+/* Call with group->mark_mutex held, releases it */
static int create_chunk(struct inode *inode, struct audit_tree *tree)
{
struct fsnotify_mark *entry;
struct audit_chunk *chunk = alloc_chunk(1);
- if (!chunk)
+
+ if (!chunk) {
+ mutex_unlock(&audit_tree_group->mark_mutex);
return -ENOMEM;
+ }

entry = &chunk->mark;
- if (fsnotify_add_inode_mark(entry, inode, 0)) {
+ if (fsnotify_add_inode_mark_locked(entry, inode, 0)) {
+ mutex_unlock(&audit_tree_group->mark_mutex);
fsnotify_put_mark(entry);
return -ENOSPC;
}

- mutex_lock(&entry->group->mark_mutex);
spin_lock(&hash_lock);
if (tree->goner) {
spin_unlock(&hash_lock);
chunk->dead = 1;
- mutex_unlock(&entry->group->mark_mutex);
+ mutex_unlock(&audit_tree_group->mark_mutex);
fsnotify_destroy_mark(entry, audit_tree_group);
fsnotify_put_mark(entry);
return 0;
@@ -375,7 +379,7 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree)
}
insert_hash(chunk);
spin_unlock(&hash_lock);
- mutex_unlock(&entry->group->mark_mutex);
+ mutex_unlock(&audit_tree_group->mark_mutex);
fsnotify_put_mark(entry); /* drop initial reference */
return 0;
}
@@ -389,6 +393,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
struct node *p;
int n;

+ mutex_lock(&audit_tree_group->mark_mutex);
old_entry = fsnotify_find_mark(&inode->i_fsnotify_marks,
audit_tree_group);
if (!old_entry)
@@ -401,6 +406,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
for (n = 0; n < old->count; n++) {
if (old->owners[n].owner == tree) {
spin_unlock(&hash_lock);
+ mutex_unlock(&audit_tree_group->mark_mutex);
fsnotify_put_mark(old_entry);
return 0;
}
@@ -409,20 +415,20 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)

chunk = alloc_chunk(old->count + 1);
if (!chunk) {
+ mutex_unlock(&audit_tree_group->mark_mutex);
fsnotify_put_mark(old_entry);
return -ENOMEM;
}

chunk_entry = &chunk->mark;

- mutex_lock(&old_entry->group->mark_mutex);
/*
* mark_mutex protects mark from getting detached and thus also from
* mark->connector->obj getting NULL.
*/
if (!(old_entry->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
/* old_entry is being shot, lets just lie */
- mutex_unlock(&old_entry->group->mark_mutex);
+ mutex_unlock(&audit_tree_group->mark_mutex);
fsnotify_put_mark(old_entry);
fsnotify_put_mark(&chunk->mark);
return -ENOENT;
@@ -430,7 +436,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)

if (fsnotify_add_mark_locked(chunk_entry, old_entry->connector->obj,
FSNOTIFY_OBJ_TYPE_INODE, 1)) {
- mutex_unlock(&old_entry->group->mark_mutex);
+ mutex_unlock(&audit_tree_group->mark_mutex);
fsnotify_put_mark(chunk_entry);
fsnotify_put_mark(old_entry);
return -ENOSPC;
@@ -440,7 +446,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
if (tree->goner) {
spin_unlock(&hash_lock);
chunk->dead = 1;
- mutex_unlock(&old_entry->group->mark_mutex);
+ mutex_unlock(&audit_tree_group->mark_mutex);

fsnotify_destroy_mark(chunk_entry, audit_tree_group);

@@ -471,7 +477,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
list_add(&tree->same_root, &chunk->trees);
}
spin_unlock(&hash_lock);
- mutex_unlock(&old_entry->group->mark_mutex);
+ mutex_unlock(&audit_tree_group->mark_mutex);
fsnotify_destroy_mark(old_entry, audit_tree_group);
fsnotify_put_mark(chunk_entry); /* drop initial reference */
fsnotify_put_mark(old_entry); /* pair to fsnotify_find mark_entry */
--
2.16.4