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fsnotify: Fix possible use-after-free in inode iteration on umount

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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 <jack@suse.cz>
This commit is contained in:
Jan Kara 2016-12-12 16:08:41 +01:00
parent b46dc03381
commit 5716863e0f
1 changed files with 9 additions and 36 deletions
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45
fs/notify/inode_mark.c
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@ -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);
}