This is a note to let you know that I've just added the patch titled
/dev/mem: Bail out upon SIGKILL.
to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-testing branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will be merged to the char-misc-next branch sometime soon,
after it passes testing, and the merge window is open.
If you have any questions about this process, please let me know.
>From 8619e5bdeee8b2c685d686281f2d2a6017c4bc15 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 26 Aug 2019 22:13:25 +0900
Subject: /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: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@xxxxxxxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1566825205-10703-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/mem.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index b08dc50f9f26..9eb564c002f6 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -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);
}
--
2.23.0
