firmware_loader: fix use-after-free in firmware_fallback_sysfs

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 previously 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")
Cc: stable <stable@vger.kernel.org>
Reported-by: syzbot+de271708674e2093097b@syzkaller.appspotmail.com
Tested-by: syzbot+de271708674e2093097b@syzkaller.appspotmail.com
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
Link: https://lore.kernel.org/r/20210728085107.4141-3-mail@anirudhrb.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/base/firmware_loader/firmware.h b/drivers/base/firmware_loader/firmware.h
index 63bd29fdcb9c..a3014e9e2c85 100644
--- a/drivers/base/firmware_loader/firmware.h
+++ b/drivers/base/firmware_loader/firmware.h
@@ -117,8 +117,16 @@ static inline void __fw_state_set(struct fw_priv *fw_priv,
 
 	WRITE_ONCE(fw_st->status, status);
 
-	if (status == FW_STATUS_DONE || status == FW_STATUS_ABORTED)
+	if (status == FW_STATUS_DONE || status == FW_STATUS_ABORTED) {
+#ifdef CONFIG_FW_LOADER_USER_HELPER
+		/*
+		 * Doing this here ensures that the fw_priv is deleted from
+		 * the pending list in all abort/done paths.
+		 */
+		list_del_init(&fw_priv->pending_list);
+#endif
 		complete_all(&fw_st->completion);
+	}
 }
 
 static inline void fw_state_aborted(struct fw_priv *fw_priv)