linux-kernel - Re: KASAN: invalid-free in snd_card

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Date:   Mon, 19 Sep 2022 10:30:54 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Rondreis <linhaoguo86@...il.com>
Cc:     perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: KASAN: invalid-free in snd_card_new

On Sun, 18 Sep 2022 15:01:11 +0200,
Rondreis wrote:
> 
> Hello,
> 
> When fuzzing the Linux kernel driver v6.0-rc4, the following crash was
> triggered.
> 
> HEAD commit: 7e18e42e4b280c85b76967a9106a13ca61c16179
> git tree: upstream
> 
> kernel config: https://pastebin.com/raw/xtrgsXP3
> C reproducer: https://pastebin.com/raw/w2sdQWYj
> console output: https://pastebin.com/raw/Yyf7zw2d
> 
> Basically, in the c reproducer, we use the gadget module to emulate
> attaching a USB device(vendor id: 0x1bc7, product id: 0x1206, with the
> midi function) and executing some simple sequence of system calls.
> To reproduce this crash, we utilize a third-party library to emulate
> the attaching process: https://github.com/linux-usb-gadgets/libusbgx.
> Just clone this repository, install it, and compile the c
> reproducer with ``` gcc crash.c -lusbgx -lconfig -o crash ``` will do
> the trick.
> 
> I would appreciate it if you have any idea how to solve this bug.

Could you try the patch below?  It looks like a simple double-free in
the code.


thanks,

Takashi

---
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -178,10 +178,8 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
 		return -ENOMEM;
 
 	err = snd_card_init(card, parent, idx, xid, module, extra_size);
-	if (err < 0) {
-		kfree(card);
-		return err;
-	}
+	if (err < 0)
+		return err; /* card is freed by error handler */
 
 	*card_ret = card;
 	return 0;
@@ -233,7 +231,7 @@ int snd_devm_card_new(struct device *parent, int idx, const char *xid,
 	card->managed = true;
 	err = snd_card_init(card, parent, idx, xid, module, extra_size);
 	if (err < 0) {
-		devres_free(card);
+		devres_free(card); /* in managed mode, we need to free manually */
 		return err;
 	}