In the Linux kernel, the following vulnerability has been resolved:

ntfs: fix use-after-free in ntfs_attr_find()

Patch series ntfs: fix bugs about Attribute, v2.

This patchset fixes three bugs relative to Attribute in record:

Patch 1 adds a sanity check to ensure that, attrs_offset field in first mft record loading from disk is within bounds.

Patch 2 moves the ATTR_RECORDs bounds checking earlier, to avoid dereferencing ATTR_RECORD before checking this ATTR_RECORD is within bounds.

Patch 3 adds an overflow checking to avoid possible forever loop in ntfs_attr_find().

Without patch 1 and patch 2, the kernel triggersa KASAN use-after-free detection as reported by Syzkaller.

Although one of patch 1 or patch 2 can fix this, we still need both of them. Because patch 1 fixes the root cause, and patch 2 not only fixes the direct cause, but also fixes the potential out-of-bounds bug.

This patch (of 3):

Syzkaller reported use-after-free read as follows:

BUG: KASAN: use-after-free in ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597 Read of size 2 at addr ffff88807e352009 by task syz-executor153/3607

[…] Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 print_address_description mm/kasan/report.c:317 [inline] print_report.cold+0x2ba/0x719 mm/kasan/report.c:433 kasan_report+0xb1/0x1e0 mm/kasan/report.c:495 ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597 ntfs_attr_lookup+0x1056/0x2070 fs/ntfs/attrib.c:1193 ntfs_read_inode_mount+0x89a/0x2580 fs/ntfs/inode.c:1845 ntfs_fill_super+0x1799/0x9320 fs/ntfs/super.c:2854 mount_bdev+0x34d/0x410 fs/super.c:1400 legacy_get_tree+0x105/0x220 fs/fs_context.c:610 vfs_get_tree+0x89/0x2f0 fs/super.c:1530 do_new_mount fs/namespace.c:3040 [inline] path_mount+0x1326/0x1e20 fs/namespace.c:3370 do_mount fs/namespace.c:3383 [inline] __do_sys_mount fs/namespace.c:3591 [inline] __se_sys_mount fs/namespace.c:3568 [inline] __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd […]

The buggy address belongs to the physical page: page:ffffea0001f8d400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7e350 head:ffffea0001f8d400 order:3 compound_mapcount:0 compound_pincount:0 flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff) raw: 00fff00000010200 0000000000000000 dead000000000122 ffff888011842140 raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff88807e351f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88807e351f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

ffff88807e352000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88807e352080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88807e352100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================

Kernel will loads $MFT/$DATAs first mft record in ntfs_read_inode_mount().

Yet the problem is that after loading, kernel doesnt check whether attrs_offset field is a valid value.

To be more specific, if attrs_offset field is larger than bytes_allocated field, then it may trigger the out-of-bounds read bug(reported as use-after-free bug) in ntfs_attr_find(), when kernel tries to access the corresponding mft records attribute.

This patch solves it by adding the sanity check between attrs_offset field and bytes_allocated field, after loading the first mft record.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/266bd5306286316758e6246ea0345133427b0f62
• https://git.kernel.org/stable/c/4863f815463034f588a035cfd99cdca97a4f1069
• https://git.kernel.org/stable/c/5330c423b86263ac7883fef0260b9e2229cb531e
• https://git.kernel.org/stable/c/79f3ac7dcd12c05b7539239a4c6fa229a50d786c
• https://git.kernel.org/stable/c/b825bfbbaafbe8da2037e3a778ad660c59f9e054
• https://git.kernel.org/stable/c/d0006d739738a658a9c29b438444259d9f71dfa0
• https://git.kernel.org/stable/c/d85a1bec8e8d552ab13163ca1874dcd82f3d1550
• https://git.kernel.org/stable/c/fb2004bafd1932e08d21ca604ee5844f2b7f212d