This is a note to let you know that I've just added the patch titled

firmware_loader: fix use-after-free in firmware_fallback_sysfs

to my driver-core git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git in the driver-core-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 75d95e2e39b27f733f21e6668af1c9893a97de5e Mon Sep 17 00:00:00 2001

From: Anirudh Rayabharam mail@anirudhrb.com Date: Wed, 28 Jul 2021 14:21:07 +0530 Subject: 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 --- 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(-)

diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c index 1a48be0a030e..d7d63c1aa993 100644 --- a/drivers/base/firmware_loader/fallback.c +++ b/drivers/base/firmware_loader/fallback.c @@ -89,12 +89,11 @@ 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); }

@@ -280,7 +279,6 @@ 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; @@ -513,6 +511,11 @@ static int fw_load_sysfs_fallback(struct fw_sysfs *fw_sysfs, long timeout) }

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);

@@ -538,6 +541,7 @@ static int fw_load_sysfs_fallback(struct fw_sysfs *fw_sysfs, long timeout) } else if (fw_priv->is_paged_buf && !fw_priv->data) retval = -ENOMEM;

+out: device_del(f_dev); err_put_dev: put_device(f_dev); 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) diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c index 4fdb8219cd08..68c549d71230 100644 --- a/drivers/base/firmware_loader/main.c +++ b/drivers/base/firmware_loader/main.c @@ -783,8 +783,10 @@ static void fw_abort_batch_reqs(struct firmware *fw) 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() */