Re: [syzbot] [alsa?] memory leak in snd_seq_create_port

[Takashi Iwai <tiwai@suse.de>]

On Sun, 16 Jul 2023 21:06:52 +0200,
Geraldo Nascimento wrote:
> 
> 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()

It's a bug that happened only on 6.5-rc1, so no need to bother too
much with security issue fiasco for distros.


Takashi