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Date: Thu, 22 Jul 2021 00:30:14 +0530 From: Anirudh Rayabharam <mail@...rudhrb.com> To: mcgrof@...nel.org, gregkh@...uxfoundation.org, rafael@...nel.org, skhan@...uxfoundation.org Cc: Anirudh Rayabharam <mail@...rudhrb.com>, linux-kernel@...r.kernel.org, linux-kernel-mentees@...ts.linuxfoundation.org, syzbot+de271708674e2093097b@...kaller.appspotmail.com Subject: [PATCH v5 2/2] 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 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@...kaller.appspotmail.com Tested-by: syzbot+de271708674e2093097b@...kaller.appspotmail.com Signed-off-by: Anirudh Rayabharam <mail@...rudhrb.com> --- drivers/base/firmware_loader/fallback.c | 10 +++++++--- drivers/base/firmware_loader/firmware.h | 6 +++++- drivers/base/firmware_loader/main.c | 2 ++ 3 files changed, 14 insertions(+), 4 deletions(-) diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c index bc25bb5d1ed6..f244c7b89ba5 100644 --- a/drivers/base/firmware_loader/fallback.c +++ b/drivers/base/firmware_loader/fallback.c @@ -115,10 +115,9 @@ 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' */ - 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); } @@ -304,7 +303,6 @@ 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; @@ -537,6 +535,11 @@ 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); @@ -556,6 +559,7 @@ static int fw_load_sysfs_fallback(struct fw_sysfs *fw_sysfs, long timeout) mutex_unlock(&fw_lock); } +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..36bdb413c998 100644 --- a/drivers/base/firmware_loader/firmware.h +++ b/drivers/base/firmware_loader/firmware.h @@ -117,8 +117,12 @@ 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 + 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() */ -- 2.26.2
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