4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dirk Behme <dirk.behme@xxxxxxxxxxxx>
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@xxxxxxxxxxx/
already.
Fixes: 239378f16aa1 ("Driver core: add uevent vars for devices of a class")
Cc: stable <stable@xxxxxxxxxx>
Cc: syzbot+ffa8143439596313a85a@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Ashish Sangwan <a.sangwan@xxxxxxxxxxx>
Cc: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240513050634.3964461-1-dirk.behme@xxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/base/core.c | 3 +++
1 file changed, 3 insertions(+)
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1236,8 +1236,11 @@ 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;
