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

[Christian Brauner]

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@xxxxxxxxxx: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@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> =====================================================
> 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