firmware_loader: fix use-after-free in firmware_fallback_sysfs

commit 75d95e2e39b27f733f21e6668af1c9893a97de5e upstream.

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, 8 insertions, 4 deletions

diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c
index 3f33460392eb1..5f3e5d8372590 100644
--- a/drivers/base/firmware_loader/fallback.c
+++ b/drivers/base/firmware_loader/fallback.c
@@ -86,12 +86,11 @@ static void __fw_load_abort(struct fw_priv *fw_priv)
 {
 	/*
 	 * There is a small window in which user can write to 'loading'
-	 * between loading done and disappearance of 'loading'
+	 * between loading done/aborted and disappearance of 'loading'
 	 */
-	if (fw_sysfs_done(fw_priv))
+	if (fw_state_is_aborted(fw_priv) || fw_sysfs_done(fw_priv))
 		return;
 
-	list_del_init(&fw_priv->pending_list);
 	fw_state_aborted(fw_priv);
 }
 
@@ -277,7 +276,6 @@ static ssize_t firmware_loading_store(struct device *dev,
 			 * Same logic as fw_load_abort, only the DONE bit
 			 * is ignored and we set ABORT only on failure.
 			 */
-			list_del_init(&fw_priv->pending_list);
 			if (rc) {
 				fw_state_aborted(fw_priv);
 				written = rc;
@@ -512,6 +510,11 @@ static int fw_load_sysfs_fallback(struct fw_sysfs *fw_sysfs,
 	}
 
 	mutex_lock(&fw_lock);
+	if (fw_state_is_aborted(fw_priv)) {
+		mutex_unlock(&fw_lock);
+		retval = -EINTR;
+		goto out;
+	}
 	list_add(&fw_priv->pending_list, &pending_fw_head);
 	mutex_unlock(&fw_lock);
 
@@ -537,6 +540,7 @@ static int fw_load_sysfs_fallback(struct fw_sysfs *fw_sysfs,
 	} else if (fw_priv->is_paged_buf && !fw_priv->data)
 		retval = -ENOMEM;
 
+out:
 	device_del(f_dev);
 err_put_dev:
 	put_device(f_dev);