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Date:   Sun, 16 Jul 2023 16:06:52 -0300
From:   Geraldo Nascimento <geraldogabriel@gmail.com>
To:     Takashi Iwai <tiwai@suse.de>
Cc:     syzbot <syzbot+cf8e7fa4eeec59b3d485@syzkaller.appspotmail.com>,
        alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org,
        perex@perex.cz, syzkaller-bugs@googlegroups.com, tiwai@suse.com
Subject: Re: [syzbot] [alsa?] memory leak in snd_seq_create_port
Message-ID: <ZLQ/zKgTGMHy/6Jn@geday>
References: <00000000000098ed3a0600965f89@google.com>
 <87v8ekattg.wl-tiwai@suse.de>
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On Sun, Jul 16, 2023 at 03:07:23PM +0200, Takashi Iwai wrote:
> On Sun, 16 Jul 2023 10:21:49 +0200,
> syzbot wrote:
> > 
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    3f01e9fed845 Merge tag 'linux-watchdog-6.5-rc2' of git://w..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=14b07344a80000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=75da4f0a455bdbd3
> > dashboard link: https://syzkaller.appspot.com/bug?extid=cf8e7fa4eeec59b3d485
> > compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15877dc2a80000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12905004a80000
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/441fb7ea58b8/disk-3f01e9fe.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/8fa7790ba0c3/vmlinux-3f01e9fe.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/5e7a6471dadf/bzImage-3f01e9fe.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+cf8e7fa4eeec59b3d485@syzkaller.appspotmail.com
> > 
> > Warning: Permanently added '10.128.1.1' (ED25519) to the list of known hosts.
> > executing program
> > executing program
> > BUG: memory leak
> > unreferenced object 0xffff888100877000 (size 512):
> >   comm "syz-executor257", pid 5012, jiffies 4294941742 (age 12.790s)
> >   hex dump (first 32 bytes):
> >     80 ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >   backtrace:
> >     [<ffffffff8154bf94>] kmalloc_trace+0x24/0x90 mm/slab_common.c:1076
> >     [<ffffffff83d29e28>] kmalloc include/linux/slab.h:582 [inline]
> >     [<ffffffff83d29e28>] kzalloc include/linux/slab.h:703 [inline]
> >     [<ffffffff83d29e28>] snd_seq_create_port+0x78/0x300 sound/core/seq/seq_ports.c:135
> >     [<ffffffff83d1f681>] snd_seq_ioctl_create_port+0xe1/0x2a0 sound/core/seq/seq_clientmgr.c:1324
> >     [<ffffffff83d20e5e>] snd_seq_ioctl+0x13e/0x290 sound/core/seq/seq_clientmgr.c:2327
> >     [<ffffffff81685173>] vfs_ioctl fs/ioctl.c:51 [inline]
> >     [<ffffffff81685173>] __do_sys_ioctl fs/ioctl.c:870 [inline]
> >     [<ffffffff81685173>] __se_sys_ioctl fs/ioctl.c:856 [inline]
> >     [<ffffffff81685173>] __x64_sys_ioctl+0x103/0x140 fs/ioctl.c:856
> >     [<ffffffff84a77ff9>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >     [<ffffffff84a77ff9>] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
> >     [<ffffffff84c0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > 
> > BUG: memory leak
> > unreferenced object 0xffff888106742c00 (size 512):
> >   comm "syz-executor257", pid 5013, jiffies 4294942276 (age 7.450s)
> >   hex dump (first 32 bytes):
> >     80 ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >   backtrace:
> >     [<ffffffff8154bf94>] kmalloc_trace+0x24/0x90 mm/slab_common.c:1076
> >     [<ffffffff83d29e28>] kmalloc include/linux/slab.h:582 [inline]
> >     [<ffffffff83d29e28>] kzalloc include/linux/slab.h:703 [inline]
> >     [<ffffffff83d29e28>] snd_seq_create_port+0x78/0x300 sound/core/seq/seq_ports.c:135
> >     [<ffffffff83d1f681>] snd_seq_ioctl_create_port+0xe1/0x2a0 sound/core/seq/seq_clientmgr.c:1324
> >     [<ffffffff83d20e5e>] snd_seq_ioctl+0x13e/0x290 sound/core/seq/seq_clientmgr.c:2327
> >     [<ffffffff81685173>] vfs_ioctl fs/ioctl.c:51 [inline]
> >     [<ffffffff81685173>] __do_sys_ioctl fs/ioctl.c:870 [inline]
> >     [<ffffffff81685173>] __se_sys_ioctl fs/ioctl.c:856 [inline]
> >     [<ffffffff81685173>] __x64_sys_ioctl+0x103/0x140 fs/ioctl.c:856
> >     [<ffffffff84a77ff9>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >     [<ffffffff84a77ff9>] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
> >     [<ffffffff84c0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Likely a forgotten kfree() at the error path.
> The patch below should fix it.
> 
> 
> Takashi
> 
> -- 8< --
> From: Takashi Iwai <tiwai@suse.de>
> Subject: [PATCH] ALSA: seq: Fix memory leak at error path in
>  snd_seq_create_port()
> 
> We forgot to release a newly allocated item at the error path in
> snd_seq_create_port().  This patch fixes it.

Thanks for the clarification and quick proposed resolution Takashi. As
an ALSA novice these bots always stunt me, personally. I understand how
helpful they are however, even if cryptic.

But shouldn't this be reported to security? It's always prone to bad
stuff when we forget a kfree()

Thanks,
Geraldo Nascimento

> 
> Reported-by: syzbot+cf8e7fa4eeec59b3d485@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/r/00000000000098ed3a0600965f89@google.com
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
>  sound/core/seq/seq_ports.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/sound/core/seq/seq_ports.c b/sound/core/seq/seq_ports.c
> index 9b80f8275026..f3f14ff0f80f 100644
> --- a/sound/core/seq/seq_ports.c
> +++ b/sound/core/seq/seq_ports.c
> @@ -149,6 +149,7 @@ int snd_seq_create_port(struct snd_seq_client *client, int port,
>  	write_lock_irq(&client->ports_lock);
>  	list_for_each_entry(p, &client->ports_list_head, list) {
>  		if (p->addr.port == port) {
> +			kfree(new_port);
>  			num = -EBUSY;
>  			goto unlock;
>  		}
> -- 
> 2.35.3
>