* [PATCH] nilfs: Avoid use-after-free caused by nilfs->ns_writer
@ 2022-11-03 14:17 ` Shigeru Yoshida
0 siblings, 0 replies; 4+ messages in thread
From: Shigeru Yoshida @ 2022-11-03 14:17 UTC (permalink / raw)
To: konishi.ryusuke
Cc: linux-nilfs, linux-kernel, syzkaller-bugs, Shigeru Yoshida,
syzbot+f816fa82f8783f7a02bb
syzbot reported use-after-free in nilfs_segctor_sync() [1].
The use-after-free occurs with nilfs->ns_writer. The scenario for the
issue is as follows:
Task1 Task2
----------------------------------------------------------------------
nilfs_construct_segment
nilfs_segctor_sync
init_wait
init_waitqueue_entry
add_wait_queue
schedule
nilfs_detach_log_writer
nilfs_segctor_destroy
kfree
finish_wait
_raw_spin_lock_irqsave
__raw_spin_lock_irqsave
do_raw_spin_lock
debug_spin_lock_before <-- use-after-free
While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After
Task1 waked up, Task1 accesses nilfs->ns_writer which is already
freed.
This patch fixes the issue by taking nilfs->ns_segctor_sem in
nilfs_construct_segment() so that nilfs->ns_segctor_sem cannot be
freed while nilfs_segctor_sync() is sleeping.
Link: https://syzkaller.appspot.com/bug?id=79a4c002e960419ca173d55e863bd09e8112df8b [1]
Reported-by: syzbot+f816fa82f8783f7a02bb@syzkaller.appspotmail.com
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
---
fs/nilfs2/segment.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index b4cebad21b48..d4f10d82664d 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -2239,16 +2239,24 @@ static void nilfs_segctor_wakeup(struct nilfs_sc_info *sci, int err)
int nilfs_construct_segment(struct super_block *sb)
{
struct the_nilfs *nilfs = sb->s_fs_info;
- struct nilfs_sc_info *sci = nilfs->ns_writer;
+ struct nilfs_sc_info *sci;
struct nilfs_transaction_info *ti;
+ int ret;
- if (!sci)
+ down_write(&nilfs->ns_segctor_sem);
+ sci = nilfs->ns_writer;
+ if (!sci) {
+ up_write(&nilfs->ns_segctor_sem);
return -EROFS;
+ }
/* A call inside transactions causes a deadlock. */
BUG_ON((ti = current->journal_info) && ti->ti_magic == NILFS_TI_MAGIC);
- return nilfs_segctor_sync(sci);
+ ret = nilfs_segctor_sync(sci);
+ up_write(&nilfs->ns_segctor_sem);
+
+ return ret;
}
/**
--
2.37.3
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH] nilfs: Avoid use-after-free caused by nilfs->ns_writer
@ 2022-11-03 14:17 ` Shigeru Yoshida
0 siblings, 0 replies; 4+ messages in thread
From: Shigeru Yoshida @ 2022-11-03 14:17 UTC (permalink / raw)
To: konishi.ryusuke-Re5JQEeQqe8AvxtiuMwx3w
Cc: linux-nilfs-u79uwXL29TY76Z2rM5mHXA,
linux-kernel-u79uwXL29TY76Z2rM5mHXA,
syzkaller-bugs-/JYPxA39Uh5TLH3MbocFFw, Shigeru Yoshida,
syzbot+f816fa82f8783f7a02bb-Pl5Pbv+GP7P466ipTTIvnc23WoclnBCfAL8bYrjMMd8
syzbot reported use-after-free in nilfs_segctor_sync() [1].
The use-after-free occurs with nilfs->ns_writer. The scenario for the
issue is as follows:
Task1 Task2
----------------------------------------------------------------------
nilfs_construct_segment
nilfs_segctor_sync
init_wait
init_waitqueue_entry
add_wait_queue
schedule
nilfs_detach_log_writer
nilfs_segctor_destroy
kfree
finish_wait
_raw_spin_lock_irqsave
__raw_spin_lock_irqsave
do_raw_spin_lock
debug_spin_lock_before <-- use-after-free
While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After
Task1 waked up, Task1 accesses nilfs->ns_writer which is already
freed.
This patch fixes the issue by taking nilfs->ns_segctor_sem in
nilfs_construct_segment() so that nilfs->ns_segctor_sem cannot be
freed while nilfs_segctor_sync() is sleeping.
Link: https://syzkaller.appspot.com/bug?id=79a4c002e960419ca173d55e863bd09e8112df8b [1]
Reported-by: syzbot+f816fa82f8783f7a02bb-Pl5Pbv+GP7P466ipTTIvnc23WoclnBCfAL8bYrjMMd8@public.gmane.org
Signed-off-by: Shigeru Yoshida <syoshida-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
fs/nilfs2/segment.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index b4cebad21b48..d4f10d82664d 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -2239,16 +2239,24 @@ static void nilfs_segctor_wakeup(struct nilfs_sc_info *sci, int err)
int nilfs_construct_segment(struct super_block *sb)
{
struct the_nilfs *nilfs = sb->s_fs_info;
- struct nilfs_sc_info *sci = nilfs->ns_writer;
+ struct nilfs_sc_info *sci;
struct nilfs_transaction_info *ti;
+ int ret;
- if (!sci)
+ down_write(&nilfs->ns_segctor_sem);
+ sci = nilfs->ns_writer;
+ if (!sci) {
+ up_write(&nilfs->ns_segctor_sem);
return -EROFS;
+ }
/* A call inside transactions causes a deadlock. */
BUG_ON((ti = current->journal_info) && ti->ti_magic == NILFS_TI_MAGIC);
- return nilfs_segctor_sync(sci);
+ ret = nilfs_segctor_sync(sci);
+ up_write(&nilfs->ns_segctor_sem);
+
+ return ret;
}
/**
--
2.37.3
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] nilfs: Avoid use-after-free caused by nilfs->ns_writer
@ 2022-11-03 18:56 ` Ryusuke Konishi
0 siblings, 0 replies; 4+ messages in thread
From: Ryusuke Konishi @ 2022-11-03 18:56 UTC (permalink / raw)
To: Shigeru Yoshida
Cc: linux-nilfs, linux-kernel, syzkaller-bugs, syzbot+f816fa82f8783f7a02bb
On Thu, Nov 3, 2022 at 11:18 PM Shigeru Yoshida wrote:
>
> syzbot reported use-after-free in nilfs_segctor_sync() [1].
>
> The use-after-free occurs with nilfs->ns_writer. The scenario for the
> issue is as follows:
>
> Task1 Task2
> ----------------------------------------------------------------------
> nilfs_construct_segment
> nilfs_segctor_sync
> init_wait
> init_waitqueue_entry
> add_wait_queue
> schedule
> nilfs_detach_log_writer
> nilfs_segctor_destroy
> kfree
> finish_wait
> _raw_spin_lock_irqsave
> __raw_spin_lock_irqsave
> do_raw_spin_lock
> debug_spin_lock_before <-- use-after-free
>
> While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After
> Task1 waked up, Task1 accesses nilfs->ns_writer which is already
> freed.
>
> This patch fixes the issue by taking nilfs->ns_segctor_sem in
> nilfs_construct_segment() so that nilfs->ns_segctor_sem cannot be
> freed while nilfs_segctor_sync() is sleeping.
>
> Link: https://syzkaller.appspot.com/bug?id=79a4c002e960419ca173d55e863bd09e8112df8b [1]
> Reported-by: syzbot+f816fa82f8783f7a02bb@syzkaller.appspotmail.com
> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
> ---
> fs/nilfs2/segment.c | 14 +++++++++++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
> index b4cebad21b48..d4f10d82664d 100644
> --- a/fs/nilfs2/segment.c
> +++ b/fs/nilfs2/segment.c
> @@ -2239,16 +2239,24 @@ static void nilfs_segctor_wakeup(struct nilfs_sc_info *sci, int err)
> int nilfs_construct_segment(struct super_block *sb)
> {
> struct the_nilfs *nilfs = sb->s_fs_info;
> - struct nilfs_sc_info *sci = nilfs->ns_writer;
> + struct nilfs_sc_info *sci;
> struct nilfs_transaction_info *ti;
> + int ret;
>
> - if (!sci)
> + down_write(&nilfs->ns_segctor_sem);
> + sci = nilfs->ns_writer;
> + if (!sci) {
> + up_write(&nilfs->ns_segctor_sem);
> return -EROFS;
> + }
>
> /* A call inside transactions causes a deadlock. */
> BUG_ON((ti = current->journal_info) && ti->ti_magic == NILFS_TI_MAGIC);
>
> - return nilfs_segctor_sync(sci);
> + ret = nilfs_segctor_sync(sci);
> + up_write(&nilfs->ns_segctor_sem);
> +
> + return ret;
> }
>
> /**
> --
> 2.37.3
>
Thank you for your help Yoshida-san.
Your analysis of the bug cause is quite correct.
However, this patch caused deadlock for tests with fsync() or mkcp
command (i.e. nilfs_ioctl_sync).
They both call nilfs_construct_segment().
The approach implemented in this patch may not avoid the deadlock regression.
I'd like to consider other approaches.
My current thoughts are either to stop detaching ns_writer on remount
which is the root cause of the UAF races, or to introduce a refcount
on struct nilfs_sc_info.
Regards,
Ryusuke Konishi
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] nilfs: Avoid use-after-free caused by nilfs->ns_writer
@ 2022-11-03 18:56 ` Ryusuke Konishi
0 siblings, 0 replies; 4+ messages in thread
From: Ryusuke Konishi @ 2022-11-03 18:56 UTC (permalink / raw)
To: Shigeru Yoshida
Cc: linux-nilfs-u79uwXL29TY76Z2rM5mHXA,
linux-kernel-u79uwXL29TY76Z2rM5mHXA,
syzkaller-bugs-/JYPxA39Uh5TLH3MbocFFw,
syzbot+f816fa82f8783f7a02bb-Pl5Pbv+GP7P466ipTTIvnc23WoclnBCfAL8bYrjMMd8
On Thu, Nov 3, 2022 at 11:18 PM Shigeru Yoshida wrote:
>
> syzbot reported use-after-free in nilfs_segctor_sync() [1].
>
> The use-after-free occurs with nilfs->ns_writer. The scenario for the
> issue is as follows:
>
> Task1 Task2
> ----------------------------------------------------------------------
> nilfs_construct_segment
> nilfs_segctor_sync
> init_wait
> init_waitqueue_entry
> add_wait_queue
> schedule
> nilfs_detach_log_writer
> nilfs_segctor_destroy
> kfree
> finish_wait
> _raw_spin_lock_irqsave
> __raw_spin_lock_irqsave
> do_raw_spin_lock
> debug_spin_lock_before <-- use-after-free
>
> While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After
> Task1 waked up, Task1 accesses nilfs->ns_writer which is already
> freed.
>
> This patch fixes the issue by taking nilfs->ns_segctor_sem in
> nilfs_construct_segment() so that nilfs->ns_segctor_sem cannot be
> freed while nilfs_segctor_sync() is sleeping.
>
> Link: https://syzkaller.appspot.com/bug?id=79a4c002e960419ca173d55e863bd09e8112df8b [1]
> Reported-by: syzbot+f816fa82f8783f7a02bb-Pl5Pbv+GP7P466ipTTIvnc23WoclnBCfAL8bYrjMMd8@public.gmane.org
> Signed-off-by: Shigeru Yoshida <syoshida-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
> fs/nilfs2/segment.c | 14 +++++++++++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
> index b4cebad21b48..d4f10d82664d 100644
> --- a/fs/nilfs2/segment.c
> +++ b/fs/nilfs2/segment.c
> @@ -2239,16 +2239,24 @@ static void nilfs_segctor_wakeup(struct nilfs_sc_info *sci, int err)
> int nilfs_construct_segment(struct super_block *sb)
> {
> struct the_nilfs *nilfs = sb->s_fs_info;
> - struct nilfs_sc_info *sci = nilfs->ns_writer;
> + struct nilfs_sc_info *sci;
> struct nilfs_transaction_info *ti;
> + int ret;
>
> - if (!sci)
> + down_write(&nilfs->ns_segctor_sem);
> + sci = nilfs->ns_writer;
> + if (!sci) {
> + up_write(&nilfs->ns_segctor_sem);
> return -EROFS;
> + }
>
> /* A call inside transactions causes a deadlock. */
> BUG_ON((ti = current->journal_info) && ti->ti_magic == NILFS_TI_MAGIC);
>
> - return nilfs_segctor_sync(sci);
> + ret = nilfs_segctor_sync(sci);
> + up_write(&nilfs->ns_segctor_sem);
> +
> + return ret;
> }
>
> /**
> --
> 2.37.3
>
Thank you for your help Yoshida-san.
Your analysis of the bug cause is quite correct.
However, this patch caused deadlock for tests with fsync() or mkcp
command (i.e. nilfs_ioctl_sync).
They both call nilfs_construct_segment().
The approach implemented in this patch may not avoid the deadlock regression.
I'd like to consider other approaches.
My current thoughts are either to stop detaching ns_writer on remount
which is the root cause of the UAF races, or to introduce a refcount
on struct nilfs_sc_info.
Regards,
Ryusuke Konishi
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-11-03 18:56 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2022-11-03 14:17 [PATCH] nilfs: Avoid use-after-free caused by nilfs->ns_writer Shigeru Yoshida
2022-11-03 14:17 ` Shigeru Yoshida
2022-11-03 18:56 ` Ryusuke Konishi
2022-11-03 18:56 ` Ryusuke Konishi
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