[PATCH 3.12 009/142] Btrfs: Fix memory corruption by ulist_add_merge() on 32bit arch

From: Jiri Slaby
Date: Fri Sep 26 2014 - 06:38:45 EST

From: Takashi Iwai <tiwai@xxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.


commit 4eb1f66dce6c4dc28dd90a7ffbe6b2b1cb08aa4e upstream.

We've got bug reports that btrfs crashes when quota is enabled on
32bit kernel, typically with the Oops like below:
BUG: unable to handle kernel NULL pointer dereference at 00000004
IP: [<f9234590>] find_parent_nodes+0x360/0x1380 [btrfs]
*pde = 00000000
Oops: 0000 [#1] SMP
CPU: 0 PID: 151 Comm: kworker/u8:2 Tainted: G S W 3.15.2-1.gd43d97e-default #1
Workqueue: btrfs-qgroup-rescan normal_work_helper [btrfs]
task: f1478130 ti: f147c000 task.ti: f147c000
EIP: 0060:[<f9234590>] EFLAGS: 00010213 CPU: 0
EIP is at find_parent_nodes+0x360/0x1380 [btrfs]
EAX: f147dda8 EBX: f147ddb0 ECX: 00000011 EDX: 00000000
ESI: 00000000 EDI: f147dda4 EBP: f147ddf8 ESP: f147dd38
DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
CR0: 8005003b CR2: 00000004 CR3: 00bf3000 CR4: 00000690
00000000 00000000 f147dda4 00000050 00000001 00000000 00000001 00000050
00000001 00000000 d3059000 00000001 00000022 000000a8 00000000 00000000
00000000 000000a1 00000000 00000000 00000001 00000000 00000000 11800000
Call Trace:
[<f923564d>] __btrfs_find_all_roots+0x9d/0xf0 [btrfs]
[<f9237bb1>] btrfs_qgroup_rescan_worker+0x401/0x760 [btrfs]
[<f9206148>] normal_work_helper+0xc8/0x270 [btrfs]
[<c025e38b>] process_one_work+0x11b/0x390
[<c025eea1>] worker_thread+0x101/0x340
[<c026432b>] kthread+0x9b/0xb0
[<c0712a71>] ret_from_kernel_thread+0x21/0x30
[<c0264290>] kthread_create_on_node+0x110/0x110

This indicates a NULL corruption in prefs_delayed list. The further
investigation and bisection pointed that the call of ulist_add_merge()
results in the corruption.

ulist_add_merge() takes u64 as aux and writes a 64bit value into
old_aux. The callers of this function in backref.c, however, pass a
pointer of a pointer to old_aux. That is, the function overwrites
64bit value on 32bit pointer. This caused a NULL in the adjacent
variable, in this case, prefs_delayed.

Here is a quick attempt to band-aid over this: a new function,
ulist_add_merge_ptr() is introduced to pass/store properly a pointer
value instead of u64. There are still ugly void ** cast remaining
in the callers because void ** cannot be taken implicitly. But, it's
safer than explicit cast to u64, anyway.

Bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=887046
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Chris Mason <clm@xxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
fs/btrfs/backref.c | 11 +++++------
fs/btrfs/ulist.h | 15 +++++++++++++++
2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 1f4ce7ac144d..715cfa42e182 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -263,9 +263,8 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
if (ret > 0)
goto next;
- ret = ulist_add_merge(parents, eb->start,
- (uintptr_t)eie,
- (u64 *)&old, GFP_NOFS);
+ ret = ulist_add_merge_ptr(parents, eb->start,
+ eie, (void **)&old, GFP_NOFS);
if (ret < 0)
if (!ret && extent_item_pos) {
@@ -962,9 +961,9 @@ again:
goto out;
ref->inode_list = eie;
- ret = ulist_add_merge(refs, ref->parent,
- (uintptr_t)ref->inode_list,
- (u64 *)&eie, GFP_NOFS);
+ ret = ulist_add_merge_ptr(refs, ref->parent,
+ ref->inode_list,
+ (void **)&eie, GFP_NOFS);
if (ret < 0)
goto out;
if (!ret && extent_item_pos) {
diff --git a/fs/btrfs/ulist.h b/fs/btrfs/ulist.h
index fb36731074b5..3e62b57be6b5 100644
--- a/fs/btrfs/ulist.h
+++ b/fs/btrfs/ulist.h
@@ -74,6 +74,21 @@ void ulist_free(struct ulist *ulist);
int ulist_add(struct ulist *ulist, u64 val, u64 aux, gfp_t gfp_mask);
int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
u64 *old_aux, gfp_t gfp_mask);
+/* just like ulist_add_merge() but take a pointer for the aux data */
+static inline int ulist_add_merge_ptr(struct ulist *ulist, u64 val, void *aux,
+ void **old_aux, gfp_t gfp_mask)
+#if BITS_PER_LONG == 32
+ u64 old64 = (uintptr_t)*old_aux;
+ int ret = ulist_add_merge(ulist, val, (uintptr_t)aux, &old64, gfp_mask);
+ *old_aux = (void *)((uintptr_t)old64);
+ return ret;
+ return ulist_add_merge(ulist, val, (u64)aux, (u64 *)old_aux, gfp_mask);
struct ulist_node *ulist_next(struct ulist *ulist,
struct ulist_iterator *uiter);


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