Re: [syzbot] [btrfs?] KMSAN: kernel-infoleak in btrfs_ioctl_logical_to_ino (2)

David Sterba
2024-04-16T17:04:21Z

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@syzkaller.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.