KASAN: invalid-free in snd_card_new

KASAN: invalid-free in snd_card_new

[Rondreis]

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.

The crash report is as follows:

==================================================================
BUG: KASAN: double-free in snd_card_new+0xf9/0x130 sound/core/init.c:182

CPU: 1 PID: 7476 Comm: syz-executor.2 Not tainted 6.0.0-rc4+ #20
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:317 [inline]
 print_report.cold+0xe5/0x66d mm/kasan/report.c:433
 kasan_report_invalid_free+0x5b/0x160 mm/kasan/report.c:462
 ____kasan_slab_free mm/kasan/common.c:356 [inline]
 __kasan_slab_free+0x179/0x1b0 mm/kasan/common.c:375
 kasan_slab_free include/linux/kasan.h:200 [inline]
 slab_free_hook mm/slub.c:1754 [inline]
 slab_free_freelist_hook mm/slub.c:1780 [inline]
 slab_free mm/slub.c:3534 [inline]
 kfree+0xe9/0x650 mm/slub.c:4562
 snd_card_new+0xf9/0x130 sound/core/init.c:182
 snd_usb_audio_create sound/usb/card.c:621 [inline]
 usb_audio_probe+0x162a/0x2f10 sound/usb/card.c:797
 usb_probe_interface+0x361/0x800 drivers/usb/core/driver.c:396
 call_driver_probe drivers/base/dd.c:560 [inline]
 really_probe+0x249/0xa90 drivers/base/dd.c:639
 __driver_probe_device+0x1df/0x4d0 drivers/base/dd.c:778
 driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:808
 __device_attach_driver+0x1da/0x2d0 drivers/base/dd.c:936
 bus_for_each_drv+0x15f/0x1e0 drivers/base/bus.c:427
 __device_attach+0x283/0x480 drivers/base/dd.c:1008
 proc_ioctl drivers/usb/core/devio.c:2356 [inline]
 proc_ioctl+0x5b4/0x6e0 drivers/usb/core/devio.c:2307
 proc_ioctl_default drivers/usb/core/devio.c:2391 [inline]
 usbdev_do_ioctl drivers/usb/core/devio.c:2747 [inline]
 usbdev_ioctl+0x29a3/0x3340 drivers/usb/core/devio.c:2807
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f0dda8a80fd
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f0ddaf63bf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f0dda99c340 RCX: 00007f0dda8a80fd
RDX: 0000000020000900 RSI: 00000000c0105512 RDI: 0000000000000003
RBP: 00007f0ddaf63c50 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000d
R13: 00007ffeb548e29f R14: 00007ffeb548e440 R15: 00007f0ddaf63d80
 </TASK>

Allocated by task 7476:
 kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:437 [inline]
 ____kasan_kmalloc mm/kasan/common.c:516 [inline]
 ____kasan_kmalloc mm/kasan/common.c:475 [inline]
 __kasan_kmalloc+0xa9/0xd0 mm/kasan/common.c:525
 kasan_kmalloc include/linux/kasan.h:234 [inline]
 __kmalloc+0x1da/0x3f0 mm/slub.c:4424
 kmalloc include/linux/slab.h:605 [inline]
 kzalloc include/linux/slab.h:733 [inline]
 snd_card_new+0x78/0x130 sound/core/init.c:176
 snd_usb_audio_create sound/usb/card.c:621 [inline]
 usb_audio_probe+0x162a/0x2f10 sound/usb/card.c:797
 usb_probe_interface+0x361/0x800 drivers/usb/core/driver.c:396
 call_driver_probe drivers/base/dd.c:560 [inline]
 really_probe+0x249/0xa90 drivers/base/dd.c:639
 __driver_probe_device+0x1df/0x4d0 drivers/base/dd.c:778
 driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:808
 __device_attach_driver+0x1da/0x2d0 drivers/base/dd.c:936
 bus_for_each_drv+0x15f/0x1e0 drivers/base/bus.c:427
 __device_attach+0x283/0x480 drivers/base/dd.c:1008
 proc_ioctl drivers/usb/core/devio.c:2356 [inline]
 proc_ioctl+0x5b4/0x6e0 drivers/usb/core/devio.c:2307
 proc_ioctl_default drivers/usb/core/devio.c:2391 [inline]
 usbdev_do_ioctl drivers/usb/core/devio.c:2747 [inline]
 usbdev_ioctl+0x29a3/0x3340 drivers/usb/core/devio.c:2807
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 7476:
 kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38
 kasan_set_track+0x21/0x30 mm/kasan/common.c:45
 kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:370
 ____kasan_slab_free mm/kasan/common.c:367 [inline]
 ____kasan_slab_free mm/kasan/common.c:329 [inline]
 __kasan_slab_free+0x11d/0x1b0 mm/kasan/common.c:375
 kasan_slab_free include/linux/kasan.h:200 [inline]
 slab_free_hook mm/slub.c:1754 [inline]
 slab_free_freelist_hook mm/slub.c:1780 [inline]
 slab_free mm/slub.c:3534 [inline]
 kfree+0xe9/0x650 mm/slub.c:4562
 snd_card_do_free sound/core/init.c:605 [inline]
 release_card_device+0x1af/0x200 sound/core/init.c:145
 device_release+0x9f/0x240 drivers/base/core.c:2330
 kobject_cleanup lib/kobject.c:673 [inline]
 kobject_release lib/kobject.c:704 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1be/0x4c0 lib/kobject.c:721
 put_device+0x1b/0x30 drivers/base/core.c:3624
 snd_card_init+0x973/0xbd0 sound/core/init.c:367
 snd_card_new+0xa1/0x130 sound/core/init.c:180
 snd_usb_audio_create sound/usb/card.c:621 [inline]
 usb_audio_probe+0x162a/0x2f10 sound/usb/card.c:797
 usb_probe_interface+0x361/0x800 drivers/usb/core/driver.c:396
 call_driver_probe drivers/base/dd.c:560 [inline]
 really_probe+0x249/0xa90 drivers/base/dd.c:639
 __driver_probe_device+0x1df/0x4d0 drivers/base/dd.c:778
 driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:808
 __device_attach_driver+0x1da/0x2d0 drivers/base/dd.c:936
 bus_for_each_drv+0x15f/0x1e0 drivers/base/bus.c:427
 __device_attach+0x283/0x480 drivers/base/dd.c:1008
 proc_ioctl drivers/usb/core/devio.c:2356 [inline]
 proc_ioctl+0x5b4/0x6e0 drivers/usb/core/devio.c:2307
 proc_ioctl_default drivers/usb/core/devio.c:2391 [inline]
 usbdev_do_ioctl drivers/usb/core/devio.c:2747 [inline]
 usbdev_ioctl+0x29a3/0x3340 drivers/usb/core/devio.c:2807
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0x80 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

The buggy address belongs to the object at ffff888041f54000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 0 bytes inside of
 8192-byte region [ffff888041f54000, ffff888041f56000)

The buggy address belongs to the physical page:
page:ffffea000107d400 refcount:1 mapcount:0 mapping:0000000000000000
index:0x0 pfn:0x41f50
head:ffffea000107d400 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x4fff00000010200(slab|head|node=1|zone=1|lastcpupid=0x7ff)
raw: 04fff00000010200 ffffea0001092200 dead000000000004 ffff888011c42280
raw: 0000000000000000 0000000080020002 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask
0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC),
pid 1, tgid 1 (swapper/0), ts 14941420612, free_ts 14728973666
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook mm/page_alloc.c:2525 [inline]
 prep_new_page+0x2c6/0x350 mm/page_alloc.c:2532
 get_page_from_freelist+0xae9/0x3a80 mm/page_alloc.c:4283
 __alloc_pages+0x321/0x710 mm/page_alloc.c:5515
 alloc_page_interleave+0x1e/0x250 mm/mempolicy.c:2103
 alloc_pages+0x25f/0x2f0 mm/mempolicy.c:2265
 alloc_slab_page mm/slub.c:1824 [inline]
 allocate_slab mm/slub.c:1969 [inline]
 new_slab+0x246/0x3a0 mm/slub.c:2029
 ___slab_alloc+0xa50/0x1060 mm/slub.c:3031
 __slab_alloc.isra.0+0x4d/0xa0 mm/slub.c:3118
 slab_alloc_node mm/slub.c:3209 [inline]
 slab_alloc mm/slub.c:3251 [inline]
 __kmalloc+0x388/0x3f0 mm/slub.c:4420
 kmalloc_array include/linux/slab.h:640 [inline]
 fb_show_logo_line drivers/video/fbdev/core/fbmem.c:491 [inline]
 fb_show_logo+0x1398/0x23c0 drivers/video/fbdev/core/fbmem.c:695
 fbcon_switch+0xef7/0x12a0 drivers/video/fbdev/core/fbcon.c:2183
 redraw_screen+0x2b9/0x740 drivers/tty/vt/vt.c:1021
 con2fb_init_display drivers/video/fbdev/core/fbcon.c:806 [inline]
 set_con2fb_map+0x798/0xec0 drivers/video/fbdev/core/fbcon.c:865
 do_fb_registered drivers/video/fbdev/core/fbcon.c:3012 [inline]
 fbcon_fb_registered+0x208/0x460 drivers/video/fbdev/core/fbcon.c:3028
 do_register_framebuffer drivers/video/fbdev/core/fbmem.c:1696 [inline]
 register_framebuffer+0x545/0x910 drivers/video/fbdev/core/fbmem.c:1865
 __drm_fb_helper_initial_config_and_unlock+0xdc6/0x1350
drivers/gpu/drm/drm_fb_helper.c:1910
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1449 [inline]
 free_pcp_prepare+0x5ab/0xd00 mm/page_alloc.c:1499
 free_unref_page_prepare mm/page_alloc.c:3380 [inline]
 free_unref_page+0x19/0x410 mm/page_alloc.c:3476
 __unfreeze_partials+0x3f3/0x410 mm/slub.c:2548
 qlink_free mm/kasan/quarantine.c:168 [inline]
 qlist_free_all+0x6a/0x170 mm/kasan/quarantine.c:187
 kasan_quarantine_reduce+0x13d/0x180 mm/kasan/quarantine.c:294
 __kasan_slab_alloc+0xa2/0xc0 mm/kasan/common.c:447
 kasan_slab_alloc include/linux/kasan.h:224 [inline]
 slab_post_alloc_hook+0x4d/0x4f0 mm/slab.h:727
 slab_alloc_node mm/slub.c:3243 [inline]
 slab_alloc mm/slub.c:3251 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3258 [inline]
 kmem_cache_alloc+0x151/0x360 mm/slub.c:3268
 ptlock_alloc mm/memory.c:5774 [inline]
 ptlock_init include/linux/mm.h:2261 [inline]
 pmd_ptlock_init include/linux/mm.h:2347 [inline]
 pgtable_pmd_page_ctor include/linux/mm.h:2383 [inline]
 pmd_alloc_one include/asm-generic/pgalloc.h:129 [inline]
 __pmd_alloc+0xbf/0x5b0 mm/memory.c:5225
 pmd_alloc include/linux/mm.h:2211 [inline]
 __handle_mm_fault+0x856/0x2e00 mm/memory.c:5013
 handle_mm_fault+0x322/0xa80 mm/memory.c:5151
 faultin_page mm/gup.c:990 [inline]
 __get_user_pages+0x5be/0x1250 mm/gup.c:1219
 __get_user_pages_locked mm/gup.c:1423 [inline]
 __get_user_pages_remote mm/gup.c:2133 [inline]
 __get_user_pages_remote+0x196/0x810 mm/gup.c:2109
 get_user_pages_remote+0x80/0xc0 mm/gup.c:2206
 get_arg_page+0xe4/0x2a0 fs/exec.c:222
 copy_string_kernel+0x16d/0x4f0 fs/exec.c:639

Memory state around the buggy address:
 ffff888041f53f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888041f53f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888041f54000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888041f54080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888041f54100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Re: KASAN: invalid-free in snd_card_new

[Takashi Iwai]

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;
 	}
 

Re: KASAN: invalid-free in snd_card_new

[Takashi Iwai]

On Mon, 19 Sep 2022 10:30:54 +0200,
Takashi Iwai wrote:
> 
> 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.

A more proper patch is below.  Please give it a try.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: core: Fix double-free at snd_card_new()

During the code change to add the support for devres-managed card
instance, we put an explicit kfree(card) call at the error path in
snd_card_new().  This is needed for the early error path before the
card is initialized with the device, but is rather superfluous and
causes a double-free at the error path after the card instance is
initialized, as the destructor of the card object already contains a
kfree() call.

This patch fixes the double-free situation by removing the superfluous
kfree().  Meanwhile we need to call kfree() explicitly for the early
error path, so it's added there instead.

Fixes: e8ad415b7a55 ("ALSA: core: Add managed card creation")
Reported-by: Rondreis <linhaoguo86@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/CAB7eexL1zBnB636hwS27d-LdPYZ_R1-5fJS_h=ZbCWYU=UPWJg@mail.gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/init.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/sound/core/init.c b/sound/core/init.c
index 193dae361fac..5377f94eb211 100644
--- 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;
 	}
 
@@ -297,6 +295,8 @@ static int snd_card_init(struct snd_card *card, struct device *parent,
 		mutex_unlock(&snd_card_mutex);
 		dev_err(parent, "cannot find the slot for index %d (range 0-%i), error: %d\n",
 			 idx, snd_ecards_limit - 1, err);
+		if (!card->managed)
+			kfree(card); /* manually free here, as no destructor called */
 		return err;
 	}
 	set_bit(idx, snd_cards_lock);		/* lock it */
-- 
2.35.3

Re: KASAN: invalid-free in snd_card_new

[Rondreis]

Hello,

I tested this patch with the reproducer and the crash did not trigger again.

On Mon, Sep 19, 2022 at 5:24 PM Takashi Iwai <tiwai@suse.de> wrote:
>
> On Mon, 19 Sep 2022 10:30:54 +0200,
> Takashi Iwai wrote:
> >
> > 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.
>
> A more proper patch is below.  Please give it a try.
>
>
> thanks,
>
> Takashi
>
> -- 8< --
> From: Takashi Iwai <tiwai@suse.de>
> Subject: [PATCH] ALSA: core: Fix double-free at snd_card_new()
>
> During the code change to add the support for devres-managed card
> instance, we put an explicit kfree(card) call at the error path in
> snd_card_new().  This is needed for the early error path before the
> card is initialized with the device, but is rather superfluous and
> causes a double-free at the error path after the card instance is
> initialized, as the destructor of the card object already contains a
> kfree() call.
>
> This patch fixes the double-free situation by removing the superfluous
> kfree().  Meanwhile we need to call kfree() explicitly for the early
> error path, so it's added there instead.
>
> Fixes: e8ad415b7a55 ("ALSA: core: Add managed card creation")
> Reported-by: Rondreis <linhaoguo86@gmail.com>
> Cc: <stable@vger.kernel.org>
> Link: https://lore.kernel.org/r/CAB7eexL1zBnB636hwS27d-LdPYZ_R1-5fJS_h=ZbCWYU=UPWJg@mail.gmail.com
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
>  sound/core/init.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/sound/core/init.c b/sound/core/init.c
> index 193dae361fac..5377f94eb211 100644
> --- 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;
>         }
>
> @@ -297,6 +295,8 @@ static int snd_card_init(struct snd_card *card, struct device *parent,
>                 mutex_unlock(&snd_card_mutex);
>                 dev_err(parent, "cannot find the slot for index %d (range 0-%i), error: %d\n",
>                          idx, snd_ecards_limit - 1, err);
> +               if (!card->managed)
> +                       kfree(card); /* manually free here, as no destructor called */
>                 return err;
>         }
>         set_bit(idx, snd_cards_lock);           /* lock it */
> --
> 2.35.3
>

Re: KASAN: invalid-free in snd_card_new

[Takashi Iwai]

On Mon, 19 Sep 2022 13:46:43 +0200,
Rondreis wrote:
> 
> Hello,
> 
> I tested this patch with the reproducer and the crash did not trigger again.

Thanks for quick testing.
I'm going to submit and merge the fix, then.


Takashi

> 
> On Mon, Sep 19, 2022 at 5:24 PM Takashi Iwai <tiwai@suse.de> wrote:
> >
> > On Mon, 19 Sep 2022 10:30:54 +0200,
> > Takashi Iwai wrote:
> > >
> > > 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.
> >
> > A more proper patch is below.  Please give it a try.
> >
> >
> > thanks,
> >
> > Takashi
> >
> > -- 8< --
> > From: Takashi Iwai <tiwai@suse.de>
> > Subject: [PATCH] ALSA: core: Fix double-free at snd_card_new()
> >
> > During the code change to add the support for devres-managed card
> > instance, we put an explicit kfree(card) call at the error path in
> > snd_card_new().  This is needed for the early error path before the
> > card is initialized with the device, but is rather superfluous and
> > causes a double-free at the error path after the card instance is
> > initialized, as the destructor of the card object already contains a
> > kfree() call.
> >
> > This patch fixes the double-free situation by removing the superfluous
> > kfree().  Meanwhile we need to call kfree() explicitly for the early
> > error path, so it's added there instead.
> >
> > Fixes: e8ad415b7a55 ("ALSA: core: Add managed card creation")
> > Reported-by: Rondreis <linhaoguo86@gmail.com>
> > Cc: <stable@vger.kernel.org>
> > Link: https://lore.kernel.org/r/CAB7eexL1zBnB636hwS27d-LdPYZ_R1-5fJS_h=ZbCWYU=UPWJg@mail.gmail.com
> > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > ---
> >  sound/core/init.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/sound/core/init.c b/sound/core/init.c
> > index 193dae361fac..5377f94eb211 100644
> > --- 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;
> >         }
> >
> > @@ -297,6 +295,8 @@ static int snd_card_init(struct snd_card *card, struct device *parent,
> >                 mutex_unlock(&snd_card_mutex);
> >                 dev_err(parent, "cannot find the slot for index %d (range 0-%i), error: %d\n",
> >                          idx, snd_ecards_limit - 1, err);
> > +               if (!card->managed)
> > +                       kfree(card); /* manually free here, as no destructor called */
> >                 return err;
> >         }
> >         set_bit(idx, snd_cards_lock);           /* lock it */
> > --
> > 2.35.3
> >
>