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authorTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>2019-08-26 22:13:25 +0900
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-09-04 13:31:28 +0200
commit8619e5bdeee8b2c685d686281f2d2a6017c4bc15 (patch)
tree283230edb902e413d58a9b51f2e938d70aebb134 /drivers/char/mem.c
parent4feb80faf428a02d407a9ea1952004af01308765 (diff)
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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: 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>
Diffstat (limited to 'drivers/char/mem.c')
-rw-r--r--drivers/char/mem.c21
1 files changed, 21 insertions, 0 deletions
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);
}