linux-kernel - [BUG] kernel: kcov: a possible sleep-in-atomic-context bug in kcov

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Date:   Tue, 17 Dec 2019 20:56:53 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     akpm@...ux-foundation.org, ishkamiel@...il.com,
        rostedt@...dmis.org, dvyukov@...gle.com,
        andrea.parri@...rulasolutions.com, anders.roxell@...aro.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        elena.reshetova@...el.com, andreyknvl@...gle.com
Cc:     linux-kernel@...r.kernel.org
Subject: [BUG] kernel: kcov: a possible sleep-in-atomic-context bug in
 kcov_ioctl()

The kernel may sleep while holding a spinlock.
The function call path (from bottom to top) in Linux 4.19 is:

kernel/kcov.c, 237:
     vfree in kcov_put
kernel/kcov.c, 413:
     kcov_put in kcov_ioctl_locked
kernel/kcov.c, 427:
     kcov_ioctl_locked in kcov_ioctl
kernel/kcov.c, 426:
     spin_lock in kcov_ioctl

vfree() can sleep at runtime.

I am not sure how to properly fix this possible bug, so I only report it.
A possible way is to replace vfree() with kfree(), and replace related 
calls to vmalloc() with kmalloc().

This bug is found by a static analysis tool STCheck written by myself.

Best wishes,
Jia-Ju Bai