In the Linux kernel, the following vulnerability has been resolved:

drivers: core: synchronize really_probe() and dev_uevent()

Synchronize the dev->driver usage in really_probe() and dev_uevent(). These can run in different threads, what can result in the following race condition for dev->driver uninitialization:

Thread #1:

really_probe() { … probe_failed: … device_unbind_cleanup(dev) { … dev->driver = NULL; // <= Failed probe sets dev->driver to NULL … } … }

Thread #2:

dev_uevent() { … if (dev->driver) // If dev->driver is NULLed from really_probe() from here on, // after above check, the system crashes add_uevent_var(env, DRIVER=%s, dev->driver->name); … }

really_probe() holds the lock, already. So nothing needs to be done there. dev_uevent() is called with lock held, often, too. But not always. What implies that we cant add any locking in dev_uevent() itself. So fix this race by adding the lock to the non-protected path. This is the path where above race is observed:

dev_uevent+0x235/0x380 uevent_show+0x10c/0x1f0 <= Add lock here dev_attr_show+0x3a/0xa0 sysfs_kf_seq_show+0x17c/0x250 kernfs_seq_show+0x7c/0x90 seq_read_iter+0x2d7/0x940 kernfs_fop_read_iter+0xc6/0x310 vfs_read+0x5bc/0x6b0 ksys_read+0xeb/0x1b0 __x64_sys_read+0x42/0x50 x64_sys_call+0x27ad/0x2d30 do_syscall_64+0xcd/0x1d0 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Similar cases are reported by syzkaller in

https://syzkaller.appspot.com/bug?extid=ffa8143439596313a85a

But these are regarding the initialization of dev->driver

dev->driver = drv;

As this switches dev->driver to non-NULL these reports can be considered to be false-positives (which should be fixed by this commit, as well, though).

The same issue was reported and tried to be fixed back in 2015 in

https://lore.kernel.org/lkml/1421259054-2574-1-git-send-email-a.sangwan@samsung.com/

already.

Affected Software

References

• https://git.kernel.org/stable/c/08891eeaa97c079b7f95d60b62dcf0e3ce034b69
• https://git.kernel.org/stable/c/13d25e82b6d00d743c7961dcb260329f86bedf7c
• https://git.kernel.org/stable/c/760603e30bf19d7b4c28e9d81f18b54fa3b745ad
• https://git.kernel.org/stable/c/95d03d369ea647b89e950667f1c3363ea6f564e6
• https://git.kernel.org/stable/c/a42b0060d6ff2f7e59290a26d5f162a3c6329b90
• https://git.kernel.org/stable/c/bb3641a5831789d83a58a39ed4a928bcbece7080
• https://git.kernel.org/stable/c/c0a40097f0bc81deafc15f9195d1fb54595cd6d0
• https://git.kernel.org/stable/c/ec772ed7cb21b46fb132f89241682553efd0b721