linux-kernel - Re: [syzbot] [btrfs?] KMSAN: kernel-infoleak in btrfs_ioctl_logical_to

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Message-ID: <20240416165648.GS3492@twin.jikos.cz>
Date: Tue, 16 Apr 2024 18:56:49 +0200
From: David Sterba <dsterba@...e.cz>
To: syzbot <syzbot+510a1abbb8116eeb341d@...kaller.appspotmail.com>
Cc: clm@...com, dsterba@...e.com, josef@...icpanda.com,
	linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [btrfs?] KMSAN: kernel-infoleak in
 btrfs_ioctl_logical_to_ino (2)

On Tue, Apr 16, 2024 at 06:14:20AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    cef27048e5c2 Merge tag 'bcachefs-2024-04-15' of https://ev..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11a1fec7180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=87a805e655619c64
> dashboard link: https://syzkaller.appspot.com/bug?extid=510a1abbb8116eeb341d
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/fce0439cf562/disk-cef27048.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/99540e71cf72/vmlinux-cef27048.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/65fbfc2c486f/bzImage-cef27048.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+510a1abbb8116eeb341d@...kaller.appspotmail.com
> 
> BTRFS info (device loop1): first mount of filesystem c9fe44da-de57-406a-8241-57ec7d4412cf
> BTRFS info (device loop1): using crc32c (crc32c-generic) checksum algorithm
> BTRFS info (device loop1): using free-space-tree
> =====================================================
> BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
> BUG: KMSAN: kernel-infoleak in _copy_to_user+0xbc/0x110 lib/usercopy.c:40
>  instrument_copy_to_user include/linux/instrumented.h:114 [inline]
>  _copy_to_user+0xbc/0x110 lib/usercopy.c:40
>  copy_to_user include/linux/uaccess.h:191 [inline]
>  btrfs_ioctl_logical_to_ino+0x440/0x750 fs/btrfs/ioctl.c:3499
>  btrfs_ioctl+0x714/0x1260
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:904 [inline]
>  __se_sys_ioctl+0x261/0x450 fs/ioctl.c:890
>  __x64_sys_ioctl+0x96/0xe0 fs/ioctl.c:890
>  x64_sys_call+0x1883/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:17
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Uninit was created at:
>  __kmalloc_large_node+0x231/0x370 mm/slub.c:3921
>  __do_kmalloc_node mm/slub.c:3954 [inline]
>  __kmalloc_node+0xb07/0x1060 mm/slub.c:3973
>  kmalloc_node include/linux/slab.h:648 [inline]
>  kvmalloc_node+0xc0/0x2d0 mm/util.c:634
>  kvmalloc include/linux/slab.h:766 [inline]
>  init_data_container+0x49/0x1e0 fs/btrfs/backref.c:2779

2767 struct btrfs_data_container *init_data_container(u32 total_bytes)
2768 {
2769         struct btrfs_data_container *data;
2770         size_t alloc_bytes;
2771
2772         alloc_bytes = max_t(size_t, total_bytes, sizeof(*data));
2773         data = kvmalloc(alloc_bytes, GFP_KERNEL);

and then data is passed around in the ioctl.

>  btrfs_ioctl_logical_to_ino+0x17c/0x750 fs/btrfs/ioctl.c:3480
>  btrfs_ioctl+0x714/0x1260
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:904 [inline]
>  __se_sys_ioctl+0x261/0x450 fs/ioctl.c:890
>  __x64_sys_ioctl+0x96/0xe0 fs/ioctl.c:890
>  x64_sys_call+0x1883/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:17
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Bytes 40-65535 of 65536 are uninitialized

It is possible to let the ioctl allocate a big buffer but return it
filled only partially. So it should be kvcalloc.