[PATCH] cfg80211: fix debugfs rename crash

[PATCH] cfg80211: fix debugfs rename crash

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

Removing the "if (IS_ERR(dir)) dir = NULL;" check only works
if we adjust the remaining code to not rely on it being NULL.
Check IS_ERR_OR_NULL() before attempting to dereference it.

I'm not actually entirely sure this fixes the syzbot crash as
the kernel config indicates that they do have DEBUG_FS in the
kernel, but this is what I found when looking there.

Cc: stable@vger.kernel.org
Fixes: d82574a8e5a4 ("cfg80211: no need to check return value of debugfs_create functions")
Reported-by: syzbot+fd5332e429401bf42d18@syzkaller.appspotmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 net/wireless/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/wireless/core.c b/net/wireless/core.c
index 341402b4f178..ce024440fa51 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -142,7 +142,7 @@ int cfg80211_dev_rename(struct cfg80211_registered_device *rdev,
 	if (result)
 		return result;
 
-	if (rdev->wiphy.debugfsdir)
+	if (!IS_ERR_OR_NULL(rdev->wiphy.debugfsdir))
 		debugfs_rename(rdev->wiphy.debugfsdir->d_parent,
 			       rdev->wiphy.debugfsdir,
 			       rdev->wiphy.debugfsdir->d_parent, newname);
-- 
2.26.2

Re: [PATCH] cfg80211: fix debugfs rename crash

[Greg KH]

On Mon, May 25, 2020 at 11:38:17AM +0200, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
> 
> Removing the "if (IS_ERR(dir)) dir = NULL;" check only works
> if we adjust the remaining code to not rely on it being NULL.
> Check IS_ERR_OR_NULL() before attempting to dereference it.
> 
> I'm not actually entirely sure this fixes the syzbot crash as
> the kernel config indicates that they do have DEBUG_FS in the
> kernel, but this is what I found when looking there.
> 
> Cc: stable@vger.kernel.org
> Fixes: d82574a8e5a4 ("cfg80211: no need to check return value of debugfs_create functions")
> Reported-by: syzbot+fd5332e429401bf42d18@syzkaller.appspotmail.com
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> ---
>  net/wireless/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/wireless/core.c b/net/wireless/core.c
> index 341402b4f178..ce024440fa51 100644
> --- a/net/wireless/core.c
> +++ b/net/wireless/core.c
> @@ -142,7 +142,7 @@ int cfg80211_dev_rename(struct cfg80211_registered_device *rdev,
>  	if (result)
>  		return result;
>  
> -	if (rdev->wiphy.debugfsdir)
> +	if (!IS_ERR_OR_NULL(rdev->wiphy.debugfsdir))
>  		debugfs_rename(rdev->wiphy.debugfsdir->d_parent,
>  			       rdev->wiphy.debugfsdir,
>  			       rdev->wiphy.debugfsdir->d_parent, newname);

I missed that d_parent was being accessed, sorry about that.  This looks
good to me:

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>