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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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