Re: [syzbot] KMSAN: uninit-value in from_kuid

From: Alexander Potapenko <glider@google.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: syzbot <syzbot+dfac92a50024b54acaa4@syzkaller.appspotmail.com>,
	akpm@linux-foundation.org, cxfcosmos@gmail.com,
	ebiederm@xmission.com, legion@kernel.org,
	linux-kernel@vger.kernel.org, serge@hallyn.com,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] KMSAN: uninit-value in from_kuid
Date: Mon, 29 Nov 2021 13:03:50 +0100	[thread overview]
Message-ID: <CAG_fn=UNdZi=fV2Ma0kSUL8ezEopga9DgoYRHPyuWQso-GHbrQ@mail.gmail.com> (raw)
In-Reply-To: <20211129114713.at2mo64hgnlmkx3x@wittgenstein>

On Mon, Nov 29, 2021 at 12:47 PM Christian Brauner
<christian.brauner@ubuntu.com> wrote:
>
> On Sat, Nov 27, 2021 at 07:50:27AM -0800, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    425295055ce6 kmsan: core: address comments to kmsan-checks.h
> > git tree:       https://github.com/google/kmsan.git master
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1640209ab00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=2d142cdf4204061
> > dashboard link: https://syzkaller.appspot.com/bug?extid=dfac92a50024b54acaa4
> > compiler:       clang version 14.0.0 (git@github.com:llvm/llvm-project.git 0996585c8e3b3d409494eb5f1cad714b9e1f7fb5), GNU ld (GNU Binutils for Debian) 2.35.2
> > userspace arch: i386
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+dfac92a50024b54acaa4@syzkaller.appspotmail.com
> >
> > =====================================================
> > BUG: KMSAN: uninit-value in map_id_up_base kernel/user_namespace.c:335 [inline]
> > BUG: KMSAN: uninit-value in map_id_up kernel/user_namespace.c:365 [inline]
> > BUG: KMSAN: uninit-value in from_kuid+0x51d/0xbd0 kernel/user_namespace.c:413
> >  map_id_up_base kernel/user_namespace.c:335 [inline]
> >  map_id_up kernel/user_namespace.c:365 [inline]
> >  from_kuid+0x51d/0xbd0 kernel/user_namespace.c:413
> >  p9pdu_vwritef+0x15ab/0x5120 net/9p/protocol.c:398
> >  p9pdu_writef+0x23a/0x280 net/9p/protocol.c:539
> >  p9pdu_vwritef+0x21f0/0x5120 net/9p/protocol.c:490
> >  p9_client_prepare_req+0xa4b/0xff0 net/9p/client.c:709
> >  p9_client_rpc+0x278/0x1410 net/9p/client.c:740
> >  p9_client_setattr+0x115/0x2c0 net/9p/client.c:1899
> >  v9fs_vfs_setattr_dotl+0x7e2/0xd70 fs/9p/vfs_inode_dotl.c:590
> >  notify_change+0x1fe3/0x2170 fs/attr.c:410
> >  vfs_utimes+0x8aa/0xc70 fs/utimes.c:65
> >  do_utimes_path fs/utimes.c:98 [inline]
> >  do_utimes fs/utimes.c:144 [inline]
> >  __do_sys_utime32 fs/utimes.c:247 [inline]
> >  __se_sys_utime32+0x386/0x520 fs/utimes.c:235
> >  __ia32_sys_utime32+0x91/0xc0 fs/utimes.c:235
> >  do_syscall_32_irqs_on arch/x86/entry/common.c:114 [inline]
> >  __do_fast_syscall_32+0x96/0xf0 arch/x86/entry/common.c:180
> >  do_fast_syscall_32+0x34/0x70 arch/x86/entry/common.c:205
> >  do_SYSENTER_32+0x1b/0x20 arch/x86/entry/common.c:248
> >  entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
> >
> > Uninit was stored to memory at:
> >  v9fs_vfs_setattr_dotl+0x58a/0xd70 fs/9p/vfs_inode_dotl.c:567
>
> That's a bug in the 9P2000.L implementation of .setattr.
> It copies struct iattr values without checking ia_valid. That's causing
> uninitalized memory to be copied. I sent a fix to 9p for this.
>
> Christian

Thanks!

-- 
Alexander Potapenko
Software Engineer

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