* [PATCH] block: cache index instead of part self to avoid use-after-free
@ 2020-01-06 7:35 Yufen Yu
2020-01-08 15:01 ` Christoph Hellwig
2020-01-09 1:35 ` Ming Lei
0 siblings, 2 replies; 3+ messages in thread
From: Yufen Yu @ 2020-01-06 7:35 UTC (permalink / raw)
To: axboe; +Cc: linux-block, ming.lei, houtao1, hch, yi.zhang, zhengchuan
When delete partition executes concurrently with IOs issue,
it may cause use-after-free on part in disk_map_sector_rcu()
as following:
blk_account_io_start(req1) delete_partition blk_account_io_start(req2)
rcu_read_lock()
disk_map_sector_rcu
part = rcu_dereference(ptbl->part[4])
rcu_assign_pointer(ptbl->part[4], NULL);
rcu_assign_pointer(ptbl->last_lookup, NULL);
rcu_assign_pointer(ptbl->last_lookup, part);
hd_struct_kill(part)
!hd_struct_try_get
part = &rq->rq_disk->part0;
rcu_read_unlock()
__delete_partition
call_rcu
rcu_read_lock
disk_map_sector_rcu
part = rcu_dereference(ptbl->last_lookup);
delete_partition_work_fn
free(part)
hd_struct_try_get(part)
BUG_ON use-after-free
req1 try to get 'ptbl->part[4]', while the part is beening
deleted. Although the delete_partition() will set last_lookup
as NULL, req1 can overwrite it as 'part[4]' again.
After calling call_rcu() and free() for the part, req2 can
access the part by last_lookup, resulting in use after free.
In fact, this bug has been reported by syzbot:
https://lkml.org/lkml/2019/1/4/357
To fix the bug, we try to cache index of part[] instead of
part[i] itself in last_lookup. Even if the index may been
re-assign, others can either get part[i] as value of NULL,
or get the new allocated part[i] after call_rcu. Both of
them is okay.
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
---
block/genhd.c | 15 +++++++++------
block/partition-generic.c | 2 +-
include/linux/genhd.h | 3 ++-
3 files changed, 12 insertions(+), 8 deletions(-)
diff --git a/block/genhd.c b/block/genhd.c
index ff6268970ddc..97447281a4f5 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -282,18 +282,21 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
struct disk_part_tbl *ptbl;
struct hd_struct *part;
int i;
+ int last_lookup;
ptbl = rcu_dereference(disk->part_tbl);
-
- part = rcu_dereference(ptbl->last_lookup);
- if (part && sector_in_part(part, sector))
- return part;
+ last_lookup = READ_ONCE(ptbl->last_lookup);
+ if (last_lookup > 0 && last_lookup < ptbl->len) {
+ part = rcu_dereference(ptbl->part[last_lookup]);
+ if (part && sector_in_part(part, sector))
+ return part;
+ }
for (i = 1; i < ptbl->len; i++) {
part = rcu_dereference(ptbl->part[i]);
if (part && sector_in_part(part, sector)) {
- rcu_assign_pointer(ptbl->last_lookup, part);
+ WRITE_ONCE(ptbl->last_lookup, i);
return part;
}
}
@@ -1263,7 +1266,7 @@ static void disk_replace_part_tbl(struct gendisk *disk,
rcu_assign_pointer(disk->part_tbl, new_ptbl);
if (old_ptbl) {
- rcu_assign_pointer(old_ptbl->last_lookup, NULL);
+ WRITE_ONCE(old_ptbl->last_lookup, 0);
kfree_rcu(old_ptbl, rcu_head);
}
}
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 1d20c9cf213f..a9fd24ae3acb 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -284,7 +284,7 @@ void delete_partition(struct gendisk *disk, int partno)
return;
rcu_assign_pointer(ptbl->part[partno], NULL);
- rcu_assign_pointer(ptbl->last_lookup, NULL);
+ WRITE_ONCE(ptbl->last_lookup, 0);
kobject_put(part->holder_dir);
device_del(part_to_dev(part));
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 8bb63027e4d6..9be4fb8f8b8b 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -160,7 +160,8 @@ enum {
struct disk_part_tbl {
struct rcu_head rcu_head;
int len;
- struct hd_struct __rcu *last_lookup;
+ /* Cache last lookup part[] index */
+ int last_lookup;
struct hd_struct __rcu *part[];
};
--
2.17.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] block: cache index instead of part self to avoid use-after-free
2020-01-06 7:35 [PATCH] block: cache index instead of part self to avoid use-after-free Yufen Yu
@ 2020-01-08 15:01 ` Christoph Hellwig
2020-01-09 1:35 ` Ming Lei
1 sibling, 0 replies; 3+ messages in thread
From: Christoph Hellwig @ 2020-01-08 15:01 UTC (permalink / raw)
To: Yufen Yu; +Cc: axboe, linux-block, ming.lei, houtao1, hch, yi.zhang, zhengchuan
On Mon, Jan 06, 2020 at 03:35:10PM +0800, Yufen Yu wrote:
> When delete partition executes concurrently with IOs issue,
> it may cause use-after-free on part in disk_map_sector_rcu()
> as following:
>
> blk_account_io_start(req1) delete_partition blk_account_io_start(req2)
>
> rcu_read_lock()
> disk_map_sector_rcu
> part = rcu_dereference(ptbl->part[4])
> rcu_assign_pointer(ptbl->part[4], NULL);
> rcu_assign_pointer(ptbl->last_lookup, NULL);
> rcu_assign_pointer(ptbl->last_lookup, part);
>
> hd_struct_kill(part)
> !hd_struct_try_get
> part = &rq->rq_disk->part0;
> rcu_read_unlock()
> __delete_partition
> call_rcu
> rcu_read_lock
> disk_map_sector_rcu
> part = rcu_dereference(ptbl->last_lookup);
>
> delete_partition_work_fn
> free(part)
> hd_struct_try_get(part)
> BUG_ON use-after-free
>
> req1 try to get 'ptbl->part[4]', while the part is beening
> deleted. Although the delete_partition() will set last_lookup
> as NULL, req1 can overwrite it as 'part[4]' again.
>
> After calling call_rcu() and free() for the part, req2 can
> access the part by last_lookup, resulting in use after free.
>
> In fact, this bug has been reported by syzbot:
> https://lkml.org/lkml/2019/1/4/357
>
> To fix the bug, we try to cache index of part[] instead of
> part[i] itself in last_lookup. Even if the index may been
> re-assign, others can either get part[i] as value of NULL,
> or get the new allocated part[i] after call_rcu. Both of
> them is okay.
>
> Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Looks good,
Reviewed-by: Christoph Hellwig <hch@lst.de>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] block: cache index instead of part self to avoid use-after-free
2020-01-06 7:35 [PATCH] block: cache index instead of part self to avoid use-after-free Yufen Yu
2020-01-08 15:01 ` Christoph Hellwig
@ 2020-01-09 1:35 ` Ming Lei
1 sibling, 0 replies; 3+ messages in thread
From: Ming Lei @ 2020-01-09 1:35 UTC (permalink / raw)
To: Yufen Yu; +Cc: axboe, linux-block, houtao1, hch, yi.zhang, zhengchuan
On Mon, Jan 06, 2020 at 03:35:10PM +0800, Yufen Yu wrote:
> When delete partition executes concurrently with IOs issue,
> it may cause use-after-free on part in disk_map_sector_rcu()
> as following:
>
> blk_account_io_start(req1) delete_partition blk_account_io_start(req2)
>
> rcu_read_lock()
> disk_map_sector_rcu
> part = rcu_dereference(ptbl->part[4])
> rcu_assign_pointer(ptbl->part[4], NULL);
> rcu_assign_pointer(ptbl->last_lookup, NULL);
> rcu_assign_pointer(ptbl->last_lookup, part);
>
> hd_struct_kill(part)
> !hd_struct_try_get
> part = &rq->rq_disk->part0;
> rcu_read_unlock()
> __delete_partition
> call_rcu
> rcu_read_lock
> disk_map_sector_rcu
> part = rcu_dereference(ptbl->last_lookup);
>
> delete_partition_work_fn
> free(part)
> hd_struct_try_get(part)
> BUG_ON use-after-free
>
> req1 try to get 'ptbl->part[4]', while the part is beening
> deleted. Although the delete_partition() will set last_lookup
> as NULL, req1 can overwrite it as 'part[4]' again.
>
> After calling call_rcu() and free() for the part, req2 can
> access the part by last_lookup, resulting in use after free.
>
> In fact, this bug has been reported by syzbot:
> https://lkml.org/lkml/2019/1/4/357
>
> To fix the bug, we try to cache index of part[] instead of
> part[i] itself in last_lookup. Even if the index may been
> re-assign, others can either get part[i] as value of NULL,
> or get the new allocated part[i] after call_rcu. Both of
> them is okay.
>
> Signed-off-by: Yufen Yu <yuyufen@huawei.com>
> ---
> block/genhd.c | 15 +++++++++------
> block/partition-generic.c | 2 +-
> include/linux/genhd.h | 3 ++-
> 3 files changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/block/genhd.c b/block/genhd.c
> index ff6268970ddc..97447281a4f5 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -282,18 +282,21 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
> struct disk_part_tbl *ptbl;
> struct hd_struct *part;
> int i;
> + int last_lookup;
>
> ptbl = rcu_dereference(disk->part_tbl);
> -
> - part = rcu_dereference(ptbl->last_lookup);
> - if (part && sector_in_part(part, sector))
> - return part;
> + last_lookup = READ_ONCE(ptbl->last_lookup);
> + if (last_lookup > 0 && last_lookup < ptbl->len) {
> + part = rcu_dereference(ptbl->part[last_lookup]);
> + if (part && sector_in_part(part, sector))
> + return part;
> + }
>
> for (i = 1; i < ptbl->len; i++) {
> part = rcu_dereference(ptbl->part[i]);
>
> if (part && sector_in_part(part, sector)) {
> - rcu_assign_pointer(ptbl->last_lookup, part);
> + WRITE_ONCE(ptbl->last_lookup, i);
> return part;
> }
> }
> @@ -1263,7 +1266,7 @@ static void disk_replace_part_tbl(struct gendisk *disk,
> rcu_assign_pointer(disk->part_tbl, new_ptbl);
>
> if (old_ptbl) {
> - rcu_assign_pointer(old_ptbl->last_lookup, NULL);
> + WRITE_ONCE(old_ptbl->last_lookup, 0);
> kfree_rcu(old_ptbl, rcu_head);
> }
> }
> diff --git a/block/partition-generic.c b/block/partition-generic.c
> index 1d20c9cf213f..a9fd24ae3acb 100644
> --- a/block/partition-generic.c
> +++ b/block/partition-generic.c
> @@ -284,7 +284,7 @@ void delete_partition(struct gendisk *disk, int partno)
> return;
>
> rcu_assign_pointer(ptbl->part[partno], NULL);
> - rcu_assign_pointer(ptbl->last_lookup, NULL);
> + WRITE_ONCE(ptbl->last_lookup, 0);
> kobject_put(part->holder_dir);
> device_del(part_to_dev(part));
>
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 8bb63027e4d6..9be4fb8f8b8b 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -160,7 +160,8 @@ enum {
> struct disk_part_tbl {
> struct rcu_head rcu_head;
> int len;
> - struct hd_struct __rcu *last_lookup;
> + /* Cache last lookup part[] index */
> + int last_lookup;
> struct hd_struct __rcu *part[];
> };
As we discussed in the following link:
https://lore.kernel.org/linux-block/5cc465cc-d68c-088e-0729-2695279c7853@huawei.com/T/#m9a959cc91ff8c6387f83aa5c505581159b5b6571
This way works, but adding a little overhead to the fast path, one indirect
memory reference, especially ->part[->last_lookup] may take one extra cacheline.
I will post one patch to fix the issue without adding the extra overhead.
Thanks,
Ming
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-01-06 7:35 [PATCH] block: cache index instead of part self to avoid use-after-free Yufen Yu
2020-01-08 15:01 ` Christoph Hellwig
2020-01-09 1:35 ` Ming Lei
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