BPF: Fix potential bad pointer dereference in bpf_sys_bpf()
CVE: CVE-2022-50069
Component: kernel
Severity: Moderate
CVSS v3: 7.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Release date: 2022-01-01T00:00:00+00:00

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

BPF: Fix potential bad pointer dereference in bpf_sys_bpf()

The bpf_sys_bpf() helper function allows an eBPF program to load another
eBPF program from within the kernel. In this case the argument union
bpf_attr pointer (as well as the insns and license pointers inside) is a
kernel address instead of a userspace address (which is the case of a
usual bpf() syscall). To make the memory copying process in the syscall
work in both cases, bpfptr_t was introduced to wrap around the pointer
and distinguish its origin. Specifically, when copying memory contents
from a bpfptr_t, a copy_from_user() is performed in case of a userspace
address and a memcpy() is performed for a kernel address.

This can lead to problems because the in-kernel pointer is never checked
for validity. The problem happens when an eBPF syscall program tries to
call bpf_sys_bpf() to load a program but provides a bad insns pointer --
say 0xdeadbeef -- in the bpf_attr union. The helper calls __sys_bpf()
which would then call bpf_prog_load() to load the program.
bpf_prog_load() is responsible for copying the eBPF instructions to the
newly allocated memory for the program; it creates a kernel bpfptr_t for
insns and invokes copy_from_bpfptr(). Internally, all bpfptr_t
operations are backed by the corresponding sockptr_t operations, which
performs direct memcpy() on kernel pointers for copy_from/strncpy_from
operations. Therefore, the code is always happy to dereference the bad
pointer to trigger a un-handle-able page fault and in turn an oops.
However, this is not supposed to happen because at that point the eBPF
program is already verified and should not cause a memory error.

Sample KASAN trace:

[   25.685056][  T228] ==================================================================
[   25.685680][  T228] BUG: KASAN: user-memory-access in copy_from_bpfptr+0x21/0x30
[   25.686210][  T228] Read of size 80 at addr 00000000deadbeef by task poc/228
[   25.686732][  T228]
[   25.686893][  T228] CPU: 3 PID: 228 Comm: poc Not tainted 5.19.0-rc7 #7
[   25.687375][  T228] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS d55cb5a 04/01/2014
[   25.687991][  T228] Call Trace:
[   25.688223][  T228]  <TASK>
[   25.688429][  T228]  dump_stack_lvl+0x73/0x9e
[   25.688747][  T228]  print_report+0xea/0x200
[   25.689061][  T228]  ? copy_from_bpfptr+0x21/0x30
[   25.689401][  T228]  ? _printk+0x54/0x6e
[   25.689693][  T228]  ? _raw_spin_lock_irqsave+0x70/0xd0
[   25.690071][  T228]  ? copy_from_bpfptr+0x21/0x30
[   25.690412][  T228]  kasan_report+0xb5/0xe0
[   25.690716][  T228]  ? copy_from_bpfptr+0x21/0x30
[   25.691059][  T228]  kasan_check_range+0x2bd/0x2e0
[   25.691405][  T228]  ? copy_from_bpfptr+0x21/0x30
[   25.691734][  T228]  memcpy+0x25/0x60
[   25.692000][  T228]  copy_from_bpfptr+0x21/0x30
[   25.692328][  T228]  bpf_prog_load+0x604/0x9e0
[   25.692653][  T228]  ? cap_capable+0xb4/0xe0
[   25.692956][  T228]  ? security_capable+0x4f/0x70
[   25.693324][  T228]  __sys_bpf+0x3af/0x580
[   25.693635][  T228]  bpf_sys_bpf+0x45/0x240
[   25.693937][  T228]  bpf_prog_f0ec79a5a3caca46_bpf_func1+0xa2/0xbd
[   25.694394][  T228]  bpf_prog_run_pin_on_cpu+0x2f/0xb0
[   25.694756][  T228]  bpf_prog_test_run_syscall+0x146/0x1c0
[   25.695144][  T228]  bpf_prog_test_run+0x172/0x190
[   25.695487][  T228]  __sys_bpf+0x2c5/0x580
[   25.695776][  T228]  __x64_sys_bpf+0x3a/0x50
[   25.696084][  T228]  do_syscall_64+0x60/0x90
[   25.696393][  T228]  ? fpregs_assert_state_consistent+0x50/0x60
[   25.696815][  T228]  ? exit_to_user_mode_prepare+0x36/0xa0
[   25.697202][  T228]  ? syscall_exit_to_user_mode+0x20/0x40
[   25.697586][  T228]  ? do_syscall_64+0x6e/0x90
[   25.697899][  T228]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
[   25.698312][  T228] RIP: 0033:0x7f6d543fb759
[   25.698624][  T228] Code: 08 5b 89 e8 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 
---truncated---


Remediation:
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.