[syzbot] [nilfs?] KMSAN: kernel-infoleak in nilfs_ioctl_wrap_copy

[syzbot] [nilfs?] KMSAN: kernel-infoleak in nilfs_ioctl_wrap_copy

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    97e36f4aa06f Revert "sched/core: kmsan: do not instrument ..
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=106829a8c80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=46c642641b9ef616
dashboard link: https://syzkaller.appspot.com/bug?extid=132fdd2f1e1805fdc591
compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9931a9627dc6/disk-97e36f4a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1aafdb2fd6dc/vmlinux-97e36f4a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/90df5872c7ff/bzImage-97e36f4a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+132fdd2f1e1805fdc591@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:121 [inline]
BUG: KMSAN: kernel-infoleak in _copy_to_user+0xc0/0x100 lib/usercopy.c:33
 instrument_copy_to_user include/linux/instrumented.h:121 [inline]
 _copy_to_user+0xc0/0x100 lib/usercopy.c:33
 copy_to_user include/linux/uaccess.h:169 [inline]
 nilfs_ioctl_wrap_copy+0x6fa/0xc10 fs/nilfs2/ioctl.c:99
 nilfs_ioctl_get_info fs/nilfs2/ioctl.c:1173 [inline]
 nilfs_ioctl+0x2402/0x4450 fs/nilfs2/ioctl.c:1290
 nilfs_compat_ioctl+0x1b8/0x200 fs/nilfs2/ioctl.c:1343
 __do_compat_sys_ioctl fs/ioctl.c:968 [inline]
 __se_compat_sys_ioctl+0x7dd/0x1000 fs/ioctl.c:910
 __ia32_compat_sys_ioctl+0x93/0xd0 fs/ioctl.c:910
 do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
 __do_fast_syscall_32+0xa2/0x100 arch/x86/entry/common.c:178
 do_fast_syscall_32+0x37/0x80 arch/x86/entry/common.c:203
 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/common.c:246
 entry_SYSENTER_compat_after_hwframe+0x70/0x82

Uninit was created at:
 __alloc_pages+0x9f6/0xe90 mm/page_alloc.c:5572
 alloc_pages+0xab0/0xd80 mm/mempolicy.c:2287
 __get_free_pages+0x34/0xc0 mm/page_alloc.c:5599
 nilfs_ioctl_wrap_copy+0x223/0xc10 fs/nilfs2/ioctl.c:74
 nilfs_ioctl_get_info fs/nilfs2/ioctl.c:1173 [inline]
 nilfs_ioctl+0x2402/0x4450 fs/nilfs2/ioctl.c:1290
 nilfs_compat_ioctl+0x1b8/0x200 fs/nilfs2/ioctl.c:1343
 __do_compat_sys_ioctl fs/ioctl.c:968 [inline]
 __se_compat_sys_ioctl+0x7dd/0x1000 fs/ioctl.c:910
 __ia32_compat_sys_ioctl+0x93/0xd0 fs/ioctl.c:910
 do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
 __do_fast_syscall_32+0xa2/0x100 arch/x86/entry/common.c:178
 do_fast_syscall_32+0x37/0x80 arch/x86/entry/common.c:203
 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/common.c:246
 entry_SYSENTER_compat_after_hwframe+0x70/0x82

Bytes 16-127 of 3968 are uninitialized
Memory access of size 3968 starts at ffff888014534000
Data copied to user address 000000002000002f

CPU: 0 PID: 18968 Comm: syz-executor.0 Not tainted 6.2.0-syzkaller-81152-g97e36f4aa06f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/16/2023
=====================================================


---
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[PATCH] nilfs2: fix kernel-infoleak in nilfs_ioctl_wrap_copy()

[Ryusuke Konishi]

The ioctl helper function nilfs_ioctl_wrap_copy, which exchanges a
metadata array to/from user space, may copy uninitialized buffer regions
to user space memory for read-only ioctl commands NILFS_IOCTL_GET_SUINFO
and NILFS_IOCTL_GET_CPINFO.

This can occur when the element size of the user space metadata given
by the v_size member of the argument nilfs_argv structure is larger than
the size of the metadata element (nilfs_suinfo structure or nilfs_cpinfo
structure) on the file system side.

KMSAN-enabled kernels detect this issue as follows:

 BUG: KMSAN: kernel-infoleak in instrument_copy_to_user
 include/linux/instrumented.h:121 [inline]
 BUG: KMSAN: kernel-infoleak in _copy_to_user+0xc0/0x100 lib/usercopy.c:33
  instrument_copy_to_user include/linux/instrumented.h:121 [inline]
  _copy_to_user+0xc0/0x100 lib/usercopy.c:33
  copy_to_user include/linux/uaccess.h:169 [inline]
  nilfs_ioctl_wrap_copy+0x6fa/0xc10 fs/nilfs2/ioctl.c:99
  nilfs_ioctl_get_info fs/nilfs2/ioctl.c:1173 [inline]
  nilfs_ioctl+0x2402/0x4450 fs/nilfs2/ioctl.c:1290
  nilfs_compat_ioctl+0x1b8/0x200 fs/nilfs2/ioctl.c:1343
  __do_compat_sys_ioctl fs/ioctl.c:968 [inline]
  __se_compat_sys_ioctl+0x7dd/0x1000 fs/ioctl.c:910
  __ia32_compat_sys_ioctl+0x93/0xd0 fs/ioctl.c:910
  do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
  __do_fast_syscall_32+0xa2/0x100 arch/x86/entry/common.c:178
  do_fast_syscall_32+0x37/0x80 arch/x86/entry/common.c:203
  do_SYSENTER_32+0x1f/0x30 arch/x86/entry/common.c:246
  entry_SYSENTER_compat_after_hwframe+0x70/0x82

 Uninit was created at:
  __alloc_pages+0x9f6/0xe90 mm/page_alloc.c:5572
  alloc_pages+0xab0/0xd80 mm/mempolicy.c:2287
  __get_free_pages+0x34/0xc0 mm/page_alloc.c:5599
  nilfs_ioctl_wrap_copy+0x223/0xc10 fs/nilfs2/ioctl.c:74
  nilfs_ioctl_get_info fs/nilfs2/ioctl.c:1173 [inline]
  nilfs_ioctl+0x2402/0x4450 fs/nilfs2/ioctl.c:1290
  nilfs_compat_ioctl+0x1b8/0x200 fs/nilfs2/ioctl.c:1343
  __do_compat_sys_ioctl fs/ioctl.c:968 [inline]
  __se_compat_sys_ioctl+0x7dd/0x1000 fs/ioctl.c:910
  __ia32_compat_sys_ioctl+0x93/0xd0 fs/ioctl.c:910
  do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
  __do_fast_syscall_32+0xa2/0x100 arch/x86/entry/common.c:178
  do_fast_syscall_32+0x37/0x80 arch/x86/entry/common.c:203
  do_SYSENTER_32+0x1f/0x30 arch/x86/entry/common.c:246
  entry_SYSENTER_compat_after_hwframe+0x70/0x82

 Bytes 16-127 of 3968 are uninitialized
 ...

This eliminates the leak issue by initializing the page allocated as
buffer using get_zeroed_page().

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+132fdd2f1e1805fdc591@syzkaller.appspotmail.com
Link: https://lkml.kernel.org/r/000000000000a5bd2d05f63f04ae@google.com
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: stable@vger.kernel.org
---
 fs/nilfs2/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index 5ccc638ae92f..1dfbc0c34513 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -71,7 +71,7 @@ static int nilfs_ioctl_wrap_copy(struct the_nilfs *nilfs,
 	if (argv->v_index > ~(__u64)0 - argv->v_nmembs)
 		return -EINVAL;
 
-	buf = (void *)__get_free_pages(GFP_NOFS, 0);
+	buf = (void *)get_zeroed_page(GFP_NOFS);
 	if (unlikely(!buf))
 		return -ENOMEM;
 	maxmembs = PAGE_SIZE / argv->v_size;
-- 
2.34.1