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Commit 8619e5bd authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Greg Kroah-Hartman
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/dev/mem: Bail out upon SIGKILL. 

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: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: stable <stable@vger.kernel.org>
Reported-by: default avatarsyzbot <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: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 4feb80fa

drivers/char/mem.c

+21 −0
Original line number Diff line number Diff line
@@ -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);

	}