On Mon, Jul 26, 2021 at 11:27:21AM -0700, Luis Chamberlain wrote:

On Sat, Jul 24, 2021 at 05:41:34PM +0530, Anirudh Rayabharam wrote:

quoted

This use-after-free happens when a fw_priv object has been freed but
hasn't been removed from the pending list (pending_fw_head). The next
time fw_load_sysfs_fallback tries to insert into the list, it ends up
accessing the pending_list member of the previoiusly freed fw_priv.

The root cause here is that all code paths that abort the fw load
don't delete it from the pending list. For example:

	_request_firmware()
	  -> fw_abort_batch_reqs()
	      -> fw_state_aborted()

To fix this, delete the fw_priv from the list in __fw_set_state() if
the new state is DONE or ABORTED. This way, all aborts will remove
the fw_priv from the list. Accordingly, remove calls to list_del_init
that were being made before calling fw_state_(aborted|done).

Also, in fw_load_sysfs_fallback, don't add the fw_priv to the pending
list if it is already aborted. Instead, just jump out and return early.

Fixes: bcfbd3523f3c ("firmware: fix a double abort case with fw_load_sysfs_fallback")
Reported-by: syzbot+de271708674e2093097b@syzkaller.appspotmail.com
Tested-by: syzbot+de271708674e2093097b@syzkaller.appspotmail.com

Curious, how do you get syzbot to test this, I mean your custom tree?

Don't need a custom tree. You can send syzbot the git url of an existing
tree (such as linux-next or Linus' tree) and a patch to apply on that
tree before testing. This is documented here:

https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches

Of course, using a custom tree is also possible.

quoted

Signed-off-by: Anirudh Rayabharam <redacted>

With the changes Shua requested being made:

I'll implement Shua's suggestions and send a new version.

Thanks!

	- Anirudh.

Acked-by: Luis Chamberlain <mcgrof@kernel.org>

  Luis

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