* [PATCH v3] /dev/mem: Bail out upon SIGKILL.
@ 2019-08-26 13:13 Tetsuo Handa
2019-08-26 13:29 ` Greg Kroah-Hartman
0 siblings, 1 reply; 5+ messages in thread
From: Tetsuo Handa @ 2019-08-26 13:13 UTC (permalink / raw)
To: Arnd Bergmann, Greg Kroah-Hartman
Cc: linux-kernel, Linus Torvalds, Tetsuo Handa, syzbot
syzbot found that a thread can stall for minutes inside read_mem() or
write_mem() after that thread was killed by SIGKILL [1]. Reading from
iomem areas of /dev/mem can be slow, depending on the hardware.
While reading 2GB at one read() is legal, delaying termination of killed
thread for minutes is bad. Thus, allow reading/writing /dev/mem and
/dev/kmem to be preemptible and killable.
[ 1335.912419][T20577] read_mem: sz=4096 count=2134565632
[ 1335.943194][T20577] read_mem: sz=4096 count=2134561536
[ 1335.978280][T20577] read_mem: sz=4096 count=2134557440
[ 1336.011147][T20577] read_mem: sz=4096 count=2134553344
[ 1336.041897][T20577] read_mem: sz=4096 count=2134549248
Theoretically, reading/writing /dev/mem and /dev/kmem can become
"interruptible". But this patch chose "killable". Future patch will make
them "interruptible" so that we can revert to "killable" if some program
regressed.
[1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@syzkaller.appspotmail.com>
---
drivers/char/mem.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index b08dc50..9eb564c 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -97,6 +97,13 @@ void __weak unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
}
#endif
+static inline bool should_stop_iteration(void)
+{
+ if (need_resched())
+ cond_resched();
+ return fatal_signal_pending(current);
+}
+
/*
* This funcion reads the *physical* memory. The f_pos points directly to the
* memory location.
@@ -175,6 +182,8 @@ static ssize_t read_mem(struct file *file, char __user *buf,
p += sz;
count -= sz;
read += sz;
+ if (should_stop_iteration())
+ break;
}
kfree(bounce);
@@ -251,6 +260,8 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
p += sz;
count -= sz;
written += sz;
+ if (should_stop_iteration())
+ break;
}
*ppos += written;
@@ -468,6 +479,10 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
read += sz;
low_count -= sz;
count -= sz;
+ if (should_stop_iteration()) {
+ count = 0;
+ break;
+ }
}
}
@@ -492,6 +507,8 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
buf += sz;
read += sz;
p += sz;
+ if (should_stop_iteration())
+ break;
}
free_page((unsigned long)kbuf);
}
@@ -544,6 +561,8 @@ static ssize_t do_write_kmem(unsigned long p, const char __user *buf,
p += sz;
count -= sz;
written += sz;
+ if (should_stop_iteration())
+ break;
}
*ppos += written;
@@ -595,6 +614,8 @@ static ssize_t write_kmem(struct file *file, const char __user *buf,
buf += sz;
virtr += sz;
p += sz;
+ if (should_stop_iteration())
+ break;
}
free_page((unsigned long)kbuf);
}
--
1.8.3.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v3] /dev/mem: Bail out upon SIGKILL.
2019-08-26 13:13 [PATCH v3] /dev/mem: Bail out upon SIGKILL Tetsuo Handa
@ 2019-08-26 13:29 ` Greg Kroah-Hartman
2019-08-26 13:44 ` Tetsuo Handa
0 siblings, 1 reply; 5+ messages in thread
From: Greg Kroah-Hartman @ 2019-08-26 13:29 UTC (permalink / raw)
To: Tetsuo Handa; +Cc: Arnd Bergmann, linux-kernel, Linus Torvalds, syzbot
On Mon, Aug 26, 2019 at 10:13:25PM +0900, Tetsuo Handa wrote:
> syzbot found that a thread can stall for minutes inside read_mem() or
> write_mem() after that thread was killed by SIGKILL [1]. Reading from
> iomem areas of /dev/mem can be slow, depending on the hardware.
> While reading 2GB at one read() is legal, delaying termination of killed
> thread for minutes is bad. Thus, allow reading/writing /dev/mem and
> /dev/kmem to be preemptible and killable.
>
> [ 1335.912419][T20577] read_mem: sz=4096 count=2134565632
> [ 1335.943194][T20577] read_mem: sz=4096 count=2134561536
> [ 1335.978280][T20577] read_mem: sz=4096 count=2134557440
> [ 1336.011147][T20577] read_mem: sz=4096 count=2134553344
> [ 1336.041897][T20577] read_mem: sz=4096 count=2134549248
>
> Theoretically, reading/writing /dev/mem and /dev/kmem can become
> "interruptible". But this patch chose "killable". Future patch will make
> them "interruptible" so that we can revert to "killable" if some program
> regressed.
>
> [1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@syzkaller.appspotmail.com>
> ---
> drivers/char/mem.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
What changed from previous versions?
That goes below the --- line at the very least.
thanks,
greg k-h
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v3] /dev/mem: Bail out upon SIGKILL.
2019-08-26 13:29 ` Greg Kroah-Hartman
@ 2019-08-26 13:44 ` Tetsuo Handa
2019-09-04 10:19 ` Tetsuo Handa
0 siblings, 1 reply; 5+ messages in thread
From: Tetsuo Handa @ 2019-08-26 13:44 UTC (permalink / raw)
To: Greg Kroah-Hartman; +Cc: Arnd Bergmann, linux-kernel, Linus Torvalds, syzbot
On 2019/08/26 22:29, Greg Kroah-Hartman wrote:
> On Mon, Aug 26, 2019 at 10:13:25PM +0900, Tetsuo Handa wrote:
>> syzbot found that a thread can stall for minutes inside read_mem() or
>> write_mem() after that thread was killed by SIGKILL [1]. Reading from
>> iomem areas of /dev/mem can be slow, depending on the hardware.
>> While reading 2GB at one read() is legal, delaying termination of killed
>> thread for minutes is bad. Thus, allow reading/writing /dev/mem and
>> /dev/kmem to be preemptible and killable.
>>
>> [ 1335.912419][T20577] read_mem: sz=4096 count=2134565632
>> [ 1335.943194][T20577] read_mem: sz=4096 count=2134561536
>> [ 1335.978280][T20577] read_mem: sz=4096 count=2134557440
>> [ 1336.011147][T20577] read_mem: sz=4096 count=2134553344
>> [ 1336.041897][T20577] read_mem: sz=4096 count=2134549248
>>
>> Theoretically, reading/writing /dev/mem and /dev/kmem can become
>> "interruptible". But this patch chose "killable". Future patch will make
>> them "interruptible" so that we can revert to "killable" if some program
>> regressed.
>>
>> [1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e
>>
>> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>> Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@syzkaller.appspotmail.com>
>> ---
>> drivers/char/mem.c | 21 +++++++++++++++++++++
>> 1 file changed, 21 insertions(+)
>
> What changed from previous versions?
>
> That goes below the --- line at the very least.
(1) Moved fatal_signal_pending() test to end of iteration.
(2) Added need_resched() test before cond_resched().
(3) Removed -EINTR assignment because end of iteration means
that at least one byte was processed (sz > 0).
>
> thanks,
>
> greg k-h
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v3] /dev/mem: Bail out upon SIGKILL.
2019-08-26 13:44 ` Tetsuo Handa
@ 2019-09-04 10:19 ` Tetsuo Handa
2019-09-04 10:50 ` Greg Kroah-Hartman
0 siblings, 1 reply; 5+ messages in thread
From: Tetsuo Handa @ 2019-09-04 10:19 UTC (permalink / raw)
To: Greg Kroah-Hartman; +Cc: Arnd Bergmann, linux-kernel, Linus Torvalds, syzbot
Ping? Syzbot is still reporting this problem.
On 2019/08/26 22:44, Tetsuo Handa wrote:
> On 2019/08/26 22:29, Greg Kroah-Hartman wrote:
>> On Mon, Aug 26, 2019 at 10:13:25PM +0900, Tetsuo Handa wrote:
>>> syzbot found that a thread can stall for minutes inside read_mem() or
>>> write_mem() after that thread was killed by SIGKILL [1]. Reading from
>>> iomem areas of /dev/mem can be slow, depending on the hardware.
>>> While reading 2GB at one read() is legal, delaying termination of killed
>>> thread for minutes is bad. Thus, allow reading/writing /dev/mem and
>>> /dev/kmem to be preemptible and killable.
>>>
>>> [ 1335.912419][T20577] read_mem: sz=4096 count=2134565632
>>> [ 1335.943194][T20577] read_mem: sz=4096 count=2134561536
>>> [ 1335.978280][T20577] read_mem: sz=4096 count=2134557440
>>> [ 1336.011147][T20577] read_mem: sz=4096 count=2134553344
>>> [ 1336.041897][T20577] read_mem: sz=4096 count=2134549248
>>>
>>> Theoretically, reading/writing /dev/mem and /dev/kmem can become
>>> "interruptible". But this patch chose "killable". Future patch will make
>>> them "interruptible" so that we can revert to "killable" if some program
>>> regressed.
>>>
>>> [1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e
>>>
>>> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>>> Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@syzkaller.appspotmail.com>
>>> ---
>>> drivers/char/mem.c | 21 +++++++++++++++++++++
>>> 1 file changed, 21 insertions(+)
>>
>> What changed from previous versions?
>>
>> That goes below the --- line at the very least.
>
> (1) Moved fatal_signal_pending() test to end of iteration.
> (2) Added need_resched() test before cond_resched().
> (3) Removed -EINTR assignment because end of iteration means
> that at least one byte was processed (sz > 0).
>
>>
>> thanks,
>>
>> greg k-h
>>
>
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2019-09-04 10:50 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2019-08-26 13:13 [PATCH v3] /dev/mem: Bail out upon SIGKILL Tetsuo Handa
2019-08-26 13:29 ` Greg Kroah-Hartman
2019-08-26 13:44 ` Tetsuo Handa
2019-09-04 10:19 ` Tetsuo Handa
2019-09-04 10:50 ` Greg Kroah-Hartman
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