linux-kernel - Re: [PATCH] debugfs: Fix memleak in debugfs_change

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Message-ID: <2025120925-unmanaged-awoke-3c8a@gregkh>
Date: Tue, 9 Dec 2025 08:08:38 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Christian Brauner <brauner@...nel.org>, NeilBrown <neil@...wn.name>,
	Kuniyuki Iwashima <kuni1840@...il.com>,
	linux-kernel@...r.kernel.org,
	syzbot+3d7ca9c802c547f8550a@...kaller.appspotmail.com
Subject: Re: [PATCH] debugfs: Fix memleak in debugfs_change_name().

On Mon, Dec 08, 2025 at 09:45:45AM +0000, Kuniyuki Iwashima wrote:
> syzbot reported memleak in debugfs_change_name(). [0]
> 
> When lookup_noperm_unlocked() fails, new_name is leaked.
> 
> Let's fix it by reusing to kfree_const() at the end of
> debugfs_change_name().
> 
> [0]:
> BUG: memory leak
> unreferenced object 0xffff8881110bb308 (size 8):
>   comm "syz.0.17", pid 6090, jiffies 4294942958
>   hex dump (first 8 bytes):
>     2e 00 00 00 00 00 00 00                          ........
>   backtrace (crc ecfc7064):
>     kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
>     slab_post_alloc_hook mm/slub.c:4953 [inline]
>     slab_alloc_node mm/slub.c:5258 [inline]
>     __do_kmalloc_node mm/slub.c:5651 [inline]
>     __kmalloc_node_track_caller_noprof+0x3b2/0x670 mm/slub.c:5759
>     __kmemdup_nul mm/util.c:64 [inline]
>     kstrdup+0x3c/0x80 mm/util.c:84
>     kstrdup_const+0x63/0x80 mm/util.c:104
>     kvasprintf_const+0xca/0x110 lib/kasprintf.c:48
>     debugfs_change_name+0xf6/0x5d0 fs/debugfs/inode.c:854
>     cfg80211_dev_rename+0xd8/0x110 net/wireless/core.c:149
>     nl80211_set_wiphy+0x102/0x1770 net/wireless/nl80211.c:3844
>     genl_family_rcv_msg_doit+0x11e/0x190 net/netlink/genetlink.c:1115
>     genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
>     genl_rcv_msg+0x2fd/0x440 net/netlink/genetlink.c:1210
>     netlink_rcv_skb+0x93/0x1d0 net/netlink/af_netlink.c:2550
>     genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
>     netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
>     netlink_unicast+0x3a3/0x4f0 net/netlink/af_netlink.c:1344
>     netlink_sendmsg+0x335/0x6b0 net/netlink/af_netlink.c:1894
>     sock_sendmsg_nosec net/socket.c:718 [inline]
>     __sock_sendmsg net/socket.c:733 [inline]
>     ____sys_sendmsg+0x562/0x5a0 net/socket.c:2608
>     ___sys_sendmsg+0xc8/0x130 net/socket.c:2662
>     __sys_sendmsg+0xc7/0x140 net/socket.c:2694
> 
> Fixes: 833d2b3a072f7 ("Add start_renaming_two_dentries()")
> Reported-by: syzbot+3d7ca9c802c547f8550a@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/69369d82.a70a0220.38f243.009f.GAE@google.com/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
> ---
>  fs/debugfs/inode.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> index 4b263c328ed29..4005d21cf009c 100644
> --- a/fs/debugfs/inode.c
> +++ b/fs/debugfs/inode.c
> @@ -841,8 +841,10 @@ int __printf(2, 3) debugfs_change_name(struct dentry *dentry, const char *fmt, .
>  	rd.new_parent = rd.old_parent;
>  	rd.flags = RENAME_NOREPLACE;
>  	target = lookup_noperm_unlocked(&QSTR(new_name), rd.new_parent);
> -	if (IS_ERR(target))
> -		return PTR_ERR(target);
> +	if (IS_ERR(target)) {
> +		error = PTR_ERR(target);
> +		goto out_free;
> +	}
>  
>  	error = start_renaming_two_dentries(&rd, dentry, target);
>  	if (error) {
> @@ -862,6 +864,7 @@ int __printf(2, 3) debugfs_change_name(struct dentry *dentry, const char *fmt, .
>  out:
>  	dput(rd.old_parent);
>  	dput(target);
> +out_free:
>  	kfree_const(new_name);
>  	return error;
>  }
> -- 
> 2.52.0.223.gf5cc29aaa4-goog
> 

Thanks, I'll queue this up after -rc1 is out.

greg k-h