[PATCH v8 0/2] firmware_loader: fix uaf in firmware_fallback_sysfs

[PATCH v8 0/2] firmware_loader: fix uaf in firmware_fallback_sysfs

[Anirudh Rayabharam]

This series fixes the use after free in firmware_fallback_sysfs reported by
syzbot at: 
https://syzkaller.appspot.com/bug?extid=de271708674e2093097b

The first patch gets rid of the -EAGAIN return since it doesn't make
sense (see patch description for more info). The second patch goes on to
actually fix the use after free issue.

Changes in v8:
1. Added/fixed some comments as suggested by Shuah

Changes in v7:
1. Don't move the error handling code from fw_load_sysfs_fallback
   to fw_sysfs_wait_timeout to simplify the patch. Also, the move
   is unnecessary.

2. Fix the commit log for patch 1 as per Luis' suggestions.

Changes in v6:
1. v5 didn't actually remove -EAGAIN. So, fixed that.

Changes in v5:
1. Split the patch into two patches as discussed here:
   https://lore.kernel.org/lkml/20210715232105.am4wsxfclj2ufjdw@garbanzo/

Changes in v4:
Documented the reasons behind the error codes returned from
fw_sysfs_wait_timeout() as suggested by Luis Chamberlain.

Changes in v3:
Modified the patch to incorporate suggestions by Luis Chamberlain in
order to fix the root cause instead of applying a "band-aid" kind of
fix.
https://lore.kernel.org/lkml/20210403013143.GV4332@42.do-not-panic.com/

Changes in v2:
1. Fixed 1 error and 1 warning (in the commit message) reported by
checkpatch.pl. The error was regarding the format for referring to
another commit "commit <sha> ("oneline")". The warning was for line
longer than 75 chars.


Anirudh Rayabharam (2):
  firmware_loader: use -ETIMEDOUT instead of -EAGAIN in
    fw_load_sysfs_fallback
  firmware_loader: fix use-after-free in firmware_fallback_sysfs

 drivers/base/firmware_loader/fallback.c | 14 ++++++++------
 drivers/base/firmware_loader/firmware.h | 10 +++++++++-
 drivers/base/firmware_loader/main.c     |  2 ++
 3 files changed, 19 insertions(+), 7 deletions(-)

-- 
2.26.2

[PATCH v8 1/2] firmware_loader: use -ETIMEDOUT instead of -EAGAIN in fw_load_sysfs_fallback

[Anirudh Rayabharam]

The only motivation for using -EAGAIN in commit 0542ad88fbdd81bb
("firmware loader: Fix _request_firmware_load() return val for fw load
abort") was to distinguish the error from -ENOMEM, and so there is no
real reason in keeping it. -EAGAIN is typically used to tell the
userspace to try something again and in this case re-using the sysfs
loading interface cannot be retried when a timeout happens, so the
return value is also bogus.

-ETIMEDOUT is received when the wait times out and returning that
is much more telling of what the reason for the failure was. So, just
propagate that instead of returning -EAGAIN.

Suggested-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
---
 drivers/base/firmware_loader/fallback.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c
index 91899d185e31..1a48be0a030e 100644
--- a/drivers/base/firmware_loader/fallback.c
+++ b/drivers/base/firmware_loader/fallback.c
@@ -535,8 +535,6 @@ static int fw_load_sysfs_fallback(struct fw_sysfs *fw_sysfs, long timeout)
 	if (fw_state_is_aborted(fw_priv)) {
 		if (retval == -ERESTARTSYS)
 			retval = -EINTR;
-		else
-			retval = -EAGAIN;
 	} else if (fw_priv->is_paged_buf && !fw_priv->data)
 		retval = -ENOMEM;
 
-- 
2.26.2

[PATCH v8 2/2] firmware_loader: fix use-after-free in firmware_fallback_sysfs

[Anirudh Rayabharam]

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")
Reported-by: syzbot+de271708674e2093097b@syzkaller.appspotmail.com
Tested-by: syzbot+de271708674e2093097b@syzkaller.appspotmail.com
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
---
 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() */
-- 
2.26.2

Re: [PATCH v8 2/2] firmware_loader: fix use-after-free in firmware_fallback_sysfs

[Shuah Khan]

On 7/28/21 2:51 AM, Anirudh Rayabharam wrote:
> 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")
> Reported-by: syzbot+de271708674e2093097b@syzkaller.appspotmail.com
> Tested-by: syzbot+de271708674e2093097b@syzkaller.appspotmail.com
> Acked-by: Luis Chamberlain <mcgrof@kernel.org>
> Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
> ---
>   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(-)
> 

Thank you. Looks good.

Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>

thanks,
-- Shuah

Re: [PATCH v8 0/2] firmware_loader: fix uaf in firmware_fallback_sysfs

[Luis Chamberlain]

On Wed, Jul 28, 2021 at 02:21:05PM +0530, Anirudh Rayabharam wrote:
> This series fixes the use after free in firmware_fallback_sysfs reported by
> syzbot at: 
> https://syzkaller.appspot.com/bug?extid=de271708674e2093097b

Greg,

With Shua's review ammeded, this series is ready to be queued up, finally.

Anirudh, thanks for following up on all these iterations!

  Luis

Re: [PATCH v8 0/2] firmware_loader: fix uaf in firmware_fallback_sysfs

[Anirudh Rayabharam]

On Wed, Jul 28, 2021 at 01:37:09PM -0700, Luis Chamberlain wrote:
> On Wed, Jul 28, 2021 at 02:21:05PM +0530, Anirudh Rayabharam wrote:
> > This series fixes the use after free in firmware_fallback_sysfs reported by
> > syzbot at: 
> > https://syzkaller.appspot.com/bug?extid=de271708674e2093097b
> 
> Greg,
> 
> With Shua's review ammeded, this series is ready to be queued up, finally.
> 
> Anirudh, thanks for following up on all these iterations!

Thank you for your guidance throughout this series!

	- Anirudh.