1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
|
From 8f2f3eb59dff4ec538de55f2e0592fec85966aab Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.com>
Date: Thu, 6 Aug 2015 15:46:42 -0700
Subject: [PATCH] fsnotify: fix oops in fsnotify_clear_marks_by_group_flags()
fsnotify_clear_marks_by_group_flags() can race with
fsnotify_destroy_marks() so that when fsnotify_destroy_mark_locked()
drops mark_mutex, a mark from the list iterated by
fsnotify_clear_marks_by_group_flags() can be freed and thus the next
entry pointer we have cached may become stale and we dereference free
memory.
Fix the problem by first moving marks to free to a special private list
and then always free the first entry in the special list. This method
is safe even when entries from the list can disappear once we drop the
lock.
Upstream-Status: Backported
Signed-off-by: Jan Kara <jack@suse.com>
Reported-by: Ashish Sangwan <a.sangwan@samsung.com>
Reviewed-by: Ashish Sangwan <a.sangwan@samsung.com>
Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Adrian Dudau <adrian.dudau@enea.com>
---
fs/notify/mark.c | 30 +++++++++++++++++++++++++-----
1 file changed, 25 insertions(+), 5 deletions(-)
diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index 92e48c7..39ddcaf 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -412,16 +412,36 @@ void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
unsigned int flags)
{
struct fsnotify_mark *lmark, *mark;
+ LIST_HEAD(to_free);
+ /*
+ * We have to be really careful here. Anytime we drop mark_mutex, e.g.
+ * fsnotify_clear_marks_by_inode() can come and free marks. Even in our
+ * to_free list so we have to use mark_mutex even when accessing that
+ * list. And freeing mark requires us to drop mark_mutex. So we can
+ * reliably free only the first mark in the list. That's why we first
+ * move marks to free to to_free list in one go and then free marks in
+ * to_free list one by one.
+ */
mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
- if (mark->flags & flags) {
- fsnotify_get_mark(mark);
- fsnotify_destroy_mark_locked(mark, group);
- fsnotify_put_mark(mark);
- }
+ if (mark->flags & flags)
+ list_move(&mark->g_list, &to_free);
}
mutex_unlock(&group->mark_mutex);
+
+ while (1) {
+ mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
+ if (list_empty(&to_free)) {
+ mutex_unlock(&group->mark_mutex);
+ break;
+ }
+ mark = list_first_entry(&to_free, struct fsnotify_mark, g_list);
+ fsnotify_get_mark(mark);
+ fsnotify_destroy_mark_locked(mark, group);
+ mutex_unlock(&group->mark_mutex);
+ fsnotify_put_mark(mark);
+ }
}
/*
--
1.9.1
|
