[tip:smp/urgent] cpu/hotplug: Fix out-of-bounds read when setting fail state

[tip-bot for Eiichi Tsukata <tipbot@zytor.com>]

Commit-ID:  33d4a5a7a5b4d02915d765064b2319e90a11cbde
Gitweb:     https://git.kernel.org/tip/33d4a5a7a5b4d02915d765064b2319e90a11cbde
Author:     Eiichi Tsukata <devel@etsukata.com>
AuthorDate: Thu, 27 Jun 2019 11:47:32 +0900
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 27 Jun 2019 09:34:04 +0200

cpu/hotplug: Fix out-of-bounds read when setting fail state

Setting invalid value to /sys/devices/system/cpu/cpuX/hotplug/fail
can control `struct cpuhp_step *sp` address, results in the following
global-out-of-bounds read.

Reproducer:

  # echo -2 > /sys/devices/system/cpu/cpu0/hotplug/fail

KASAN report:

  BUG: KASAN: global-out-of-bounds in write_cpuhp_fail+0x2cd/0x2e0
  Read of size 8 at addr ffffffff89734438 by task bash/1941

  CPU: 0 PID: 1941 Comm: bash Not tainted 5.2.0-rc6+ #31
  Call Trace:
   write_cpuhp_fail+0x2cd/0x2e0
   dev_attr_store+0x58/0x80
   sysfs_kf_write+0x13d/0x1a0
   kernfs_fop_write+0x2bc/0x460
   vfs_write+0x1e1/0x560
   ksys_write+0x126/0x250
   do_syscall_64+0xc1/0x390
   entry_SYSCALL_64_after_hwframe+0x49/0xbe
  RIP: 0033:0x7f05e4f4c970

  The buggy address belongs to the variable:
   cpu_hotplug_lock+0x98/0xa0

  Memory state around the buggy address:
   ffffffff89734300: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
   ffffffff89734380: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
  >ffffffff89734400: 00 00 00 00 fa fa fa fa 00 00 00 00 fa fa fa fa
                                          ^
   ffffffff89734480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
   ffffffff89734500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Add a sanity check for the value written from user space.

Fixes: 1db49484f21ed ("smp/hotplug: Hotplug state fail injection")
Signed-off-by: Eiichi Tsukata <devel@etsukata.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: peterz@infradead.org
Link: https://lkml.kernel.org/r/20190627024732.31672-1-devel@etsukata.com

---
 kernel/cpu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 551db494f153..ef1c565edc5d 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1964,6 +1964,9 @@ static ssize_t write_cpuhp_fail(struct device *dev,
 	if (ret)
 		return ret;
 
+	if (fail < CPUHP_OFFLINE || fail > CPUHP_ONLINE)
+		return -EINVAL;
+
 	/*
 	 * Cannot fail STARTING/DYING callbacks.
 	 */