[PATCH 5.4 41/85] firmware_loader: fix use-after-free in firmware_fallback_sysfs

Greg Kroah-Hartman
2021-08-10T17:36:44Z

From: Anirudh Rayabharam <mail@anirudhrb.com>

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>
---
drivers/base/firmware_loader/fallback.c | 12 ++++++++----
drivers/base/firmware_loader/firmware.h | 10 +++++++++-
drivers/base/firmware_loader/main.c | 2 ++
3 files changed, 19 insertions(+), 5 deletions(-)

--- 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_pr
{
/*
* 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(st
* 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
}

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
} else if (fw_priv->is_paged_buf && !fw_priv->data)
retval = -ENOMEM;

+out:
device_del(f_dev);
err_put_dev:
put_device(f_dev);
--- a/drivers/base/firmware_loader/firmware.h
+++ b/drivers/base/firmware_loader/firmware.h
@@ -108,8 +108,16 @@ static inline void __fw_state_set(struct

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)
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -747,8 +747,10 @@ static void fw_abort_batch_reqs(struct f
return;

fw_priv = fw->priv;
+ mutex_lock(&fw_lock);
if (!fw_state_is_aborted(fw_priv))
fw_state_aborted(fw_priv);
+ mutex_unlock(&fw_lock);
}

/* called from request_firmware() and request_firmware_work_func() */