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

f2fs: fix to do sanity check on i_xattr_nid in sanity_check_inode()

syzbot reports a kernel bug as below:

F2FS-fs (loop0): Mounted with checkpoint version = 48b305e4

BUG: KASAN: slab-out-of-bounds in f2fs_test_bit fs/f2fs/f2fs.h:2933 [inline] BUG: KASAN: slab-out-of-bounds in current_nat_addr fs/f2fs/node.h:213 [inline] BUG: KASAN: slab-out-of-bounds in f2fs_get_node_info+0xece/0x1200 fs/f2fs/node.c:600 Read of size 1 at addr ffff88807a58c76c by task syz-executor280/5076

CPU: 1 PID: 5076 Comm: syz-executor280 Not tainted 6.9.0-rc5-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114 print_address_description mm/kasan/report.c:377 [inline] print_report+0x169/0x550 mm/kasan/report.c:488 kasan_report+0x143/0x180 mm/kasan/report.c:601 f2fs_test_bit fs/f2fs/f2fs.h:2933 [inline] current_nat_addr fs/f2fs/node.h:213 [inline] f2fs_get_node_info+0xece/0x1200 fs/f2fs/node.c:600 f2fs_xattr_fiemap fs/f2fs/data.c:1848 [inline] f2fs_fiemap+0x55d/0x1ee0 fs/f2fs/data.c:1925 ioctl_fiemap fs/ioctl.c:220 [inline] do_vfs_ioctl+0x1c07/0x2e50 fs/ioctl.c:838 __do_sys_ioctl fs/ioctl.c:902 [inline] __se_sys_ioctl+0x81/0x170 fs/ioctl.c:890 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The root cause is we missed to do sanity check on i_xattr_nid during f2fs_iget(), so that in fiemap() path, current_nat_addr() will access nat_bitmap w/ offset from invalid i_xattr_nid, result in triggering kasan bug report, fix it.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/1640dcf383cdba52be8b28d2a1a2aa7ef7a30c98
• https://git.kernel.org/stable/c/20faaf30e55522bba2b56d9c46689233205d7717
• https://git.kernel.org/stable/c/68e3cd4ecb8603936cccdc338929130045df2e57
• https://git.kernel.org/stable/c/75c87e2ac6149abf44bdde0dd6d541763ddb0dff
• https://git.kernel.org/stable/c/8c8aa473fe6eb46a4bf99f3ea2dbe52bf0c1a1f0
• https://git.kernel.org/stable/c/be0155202e431f3007778568a72432c68f8946ba
• https://git.kernel.org/stable/c/c559a8d840562fbfce9f318448dda2f7d3e6d8e8
• https://git.kernel.org/stable/c/1640dcf383cdba52be8b28d2a1a2aa7ef7a30c98
• https://git.kernel.org/stable/c/20faaf30e55522bba2b56d9c46689233205d7717
• https://git.kernel.org/stable/c/68e3cd4ecb8603936cccdc338929130045df2e57
• https://git.kernel.org/stable/c/75c87e2ac6149abf44bdde0dd6d541763ddb0dff
• https://git.kernel.org/stable/c/8c8aa473fe6eb46a4bf99f3ea2dbe52bf0c1a1f0
• https://git.kernel.org/stable/c/be0155202e431f3007778568a72432c68f8946ba
• https://git.kernel.org/stable/c/c559a8d840562fbfce9f318448dda2f7d3e6d8e8