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authorEric Paris <eparis@redhat.com>2009-09-11 13:03:19 -0400
committerEric Paris <eparis@redhat.com>2009-10-18 15:49:38 -0400
commit9f0d793b52eb2266359661369ef6303838904855 (patch)
treec884f59a4ad9ce50b033710d47894bc96c214a6c /fs/notify/inode_mark.c
parent2fdc246aaf9a7fa088451ad2a72e9119b5f7f029 (diff)
downloadlinux-9f0d793b52eb2266359661369ef6303838904855.tar.gz
fsnotify: do not set group for a mark before it is on the i_list
fsnotify_add_mark is supposed to add a mark to the g_list and i_list and to set the group and inode for the mark. fsnotify_destroy_mark_by_entry uses the fact that ->group != NULL to know if this group should be destroyed or if it's already been done. But fsnotify_add_mark sets the group and inode before it actually adds the mark to the i_list and g_list. This can result in a race in inotify, it requires 3 threads. sys_inotify_add_watch("file") sys_inotify_add_watch("file") sys_inotify_rm_watch([a]) inotify_update_watch() inotify_new_watch() inotify_add_to_idr() ^--- returns wd = [a] inotfiy_update_watch() inotify_new_watch() inotify_add_to_idr() fsnotify_add_mark() ^--- returns wd = [b] returns to userspace; inotify_idr_find([a]) ^--- gives us the pointer from task 1 fsnotify_add_mark() ^--- this is going to set the mark->group and mark->inode fields, but will return -EEXIST because of the race with [b]. fsnotify_destroy_mark() ^--- since ->group != NULL we call back into inotify_freeing_mark() which calls inotify_remove_from_idr([a]) since fsnotify_add_mark() failed we call: inotify_remove_from_idr([a]) <------WHOOPS it's not in the idr, this could have been any entry added later! The fix is to make sure we don't set mark->group until we are sure the mark is on the inode and fsnotify_add_mark will return success. Signed-off-by: Eric Paris <eparis@redhat.com>
Diffstat (limited to 'fs/notify/inode_mark.c')
-rw-r--r--fs/notify/inode_mark.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/fs/notify/inode_mark.c b/fs/notify/inode_mark.c
index c8a07c65482..3165d85aada 100644
--- a/fs/notify/inode_mark.c
+++ b/fs/notify/inode_mark.c
@@ -324,11 +324,11 @@ int fsnotify_add_mark(struct fsnotify_mark_entry *entry,
spin_lock(&group->mark_lock);
spin_lock(&inode->i_lock);
- entry->group = group;
- entry->inode = inode;
-
lentry = fsnotify_find_mark_entry(group, inode);
if (!lentry) {
+ entry->group = group;
+ entry->inode = inode;
+
hlist_add_head(&entry->i_list, &inode->i_fsnotify_mark_entries);
list_add(&entry->g_list, &group->mark_entries);