/dev/mem: Bail out upon SIGKILL. (8619e5bd) · Commits · 戴 / test

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>

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);
		}

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