5.4-stable review patch. If anyone has any objections, please let me know.
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From: Dirk Behme dirk.behme@de.bosch.com
commit c0a40097f0bc81deafc15f9195d1fb54595cd6d0 upstream.
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 can't 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@sams...
already.
Fixes: 239378f16aa1 ("Driver core: add uevent vars for devices of a class") Cc: stable stable@kernel.org Cc: syzbot+ffa8143439596313a85a@syzkaller.appspotmail.com Cc: Ashish Sangwan a.sangwan@samsung.com Cc: Namjae Jeon namjae.jeon@samsung.com Signed-off-by: Dirk Behme dirk.behme@de.bosch.com Link: https://lore.kernel.org/r/20240513050634.3964461-1-dirk.behme@de.bosch.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/base/core.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -1273,8 +1273,11 @@ static ssize_t uevent_show(struct device if (!env) return -ENOMEM;
+ /* Synchronize with really_probe() */ + device_lock(dev); /* let the kset specific function add its keys */ retval = kset->uevent_ops->uevent(kset, &dev->kobj, env); + device_unlock(dev); if (retval) goto out;