From 5716863e0f8251d3360d4cbfc0e44e08007075df Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Mon, 12 Dec 2016 16:08:41 +0100 Subject: [PATCH] fsnotify: Fix possible use-after-free in inode iteration on umount fsnotify_unmount_inodes() plays complex tricks to pin next inode in the sb->s_inodes list when iterating over all inodes. Furthermore the code has a bug that if the current inode is the last on i_sb_list that does not have e.g. I_FREEING set, then we leave next_i pointing to inode which may get removed from the i_sb_list once we drop s_inode_list_lock thus resulting in use-after-free issues (usually manifesting as infinite looping in fsnotify_unmount_inodes()). Fix the problem by keeping current inode pinned somewhat longer. Then we can make the code much simpler and standard. CC: stable@vger.kernel.org Signed-off-by: Jan Kara --- fs/notify/inode_mark.c | 45 +++++++++--------------------------------- 1 file changed, 9 insertions(+), 36 deletions(-) diff --git a/fs/notify/inode_mark.c b/fs/notify/inode_mark.c index 741077deef3b..a3645249f7ec 100644 --- a/fs/notify/inode_mark.c +++ b/fs/notify/inode_mark.c @@ -150,12 +150,10 @@ int fsnotify_add_inode_mark(struct fsnotify_mark *mark, */ void fsnotify_unmount_inodes(struct super_block *sb) { - struct inode *inode, *next_i, *need_iput = NULL; + struct inode *inode, *iput_inode = NULL; spin_lock(&sb->s_inode_list_lock); - list_for_each_entry_safe(inode, next_i, &sb->s_inodes, i_sb_list) { - struct inode *need_iput_tmp; - + list_for_each_entry(inode, &sb->s_inodes, i_sb_list) { /* * We cannot __iget() an inode in state I_FREEING, * I_WILL_FREE, or I_NEW which is fine because by that point @@ -178,49 +176,24 @@ void fsnotify_unmount_inodes(struct super_block *sb) continue; } - need_iput_tmp = need_iput; - need_iput = NULL; - - /* In case fsnotify_inode_delete() drops a reference. */ - if (inode != need_iput_tmp) - __iget(inode); - else - need_iput_tmp = NULL; + __iget(inode); spin_unlock(&inode->i_lock); - - /* In case the dropping of a reference would nuke next_i. */ - while (&next_i->i_sb_list != &sb->s_inodes) { - spin_lock(&next_i->i_lock); - if (!(next_i->i_state & (I_FREEING | I_WILL_FREE)) && - atomic_read(&next_i->i_count)) { - __iget(next_i); - need_iput = next_i; - spin_unlock(&next_i->i_lock); - break; - } - spin_unlock(&next_i->i_lock); - next_i = list_next_entry(next_i, i_sb_list); - } - - /* - * We can safely drop s_inode_list_lock here because either - * we actually hold references on both inode and next_i or - * end of list. Also no new inodes will be added since the - * umount has begun. - */ spin_unlock(&sb->s_inode_list_lock); - if (need_iput_tmp) - iput(need_iput_tmp); + if (iput_inode) + iput(iput_inode); /* for each watch, send FS_UNMOUNT and then remove it */ fsnotify(inode, FS_UNMOUNT, inode, FSNOTIFY_EVENT_INODE, NULL, 0); fsnotify_inode_delete(inode); - iput(inode); + iput_inode = inode; spin_lock(&sb->s_inode_list_lock); } spin_unlock(&sb->s_inode_list_lock); + + if (iput_inode) + iput(iput_inode); } -- 2.20.1