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SubjectRe: [PATCH] /dev/mem: Bail out upon SIGKILL when reading memory.
On Wed, Aug 21, 2019 at 07:06:51AM +0900, Tetsuo Handa wrote:
> syzbot found that a thread can stall for minutes inside read_mem()
> after that thread was killed by SIGKILL [1]. Reading 2GB at one read()
> is legal, but delaying termination of killed thread for minutes is bad.
>
> [ 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
>
> [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 | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> index b08dc50..0f7d4c4 100644
> --- a/drivers/char/mem.c
> +++ b/drivers/char/mem.c
> @@ -135,7 +135,7 @@ static ssize_t read_mem(struct file *file, char __user *buf,
> if (!bounce)
> return -ENOMEM;
>
> - while (count > 0) {
> + while (count > 0 && !fatal_signal_pending(current)) {
> unsigned long remaining;
> int allowed, probe;
>
> --
> 1.8.3.1
>

Oh, nice! This shouldn't break anything that is assuming that the read
will complete before a signal is delivered, right?

I know userspace handling of "short" reads is almost always not there...

thanks,

greg k-h

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