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/dev/mem: Bail out upon SIGKILL.

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commit 8619e5bdeee8b2c685d686281f2d2a6017c4bc15 upstream.

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>
Cc: stable <stable@vger.kernel.org>
Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/r/1566825205-10703-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tetsuo Handa 2019-08-26 22:13:25 +09:00 committed by Greg Kroah-Hartman
parent bd3a11af1b
commit caa6926d94
1 changed files with 21 additions and 0 deletions
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21
drivers/char/mem.c
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@ -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);
}