CVE-2022-49985

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

bpf: Don't use tnum_range on array range checking for poke descriptors

Hsin-Wei reported a KASAN splat triggered by their BPF runtime fuzzer which

is based on a customized syzkaller:

BUG: KASAN: slab-out-of-bounds in bpf_int_jit_compile+0x1257/0x13f0

Read of size 8 at addr ffff888004e90b58 by task syz-executor.0/1489

CPU: 1 PID: 1489 Comm: syz-executor.0 Not tainted 5.19.0 #1

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS

1.13.0-1ubuntu1.1 04/01/2014

Call Trace:

<TASK>

dump_stack_lvl+0x9c/0xc9

print_address_description.constprop.0+0x1f/0x1f0

? bpf_int_jit_compile+0x1257/0x13f0

kasan_report.cold+0xeb/0x197

? kvmalloc_node+0x170/0x200

? bpf_int_jit_compile+0x1257/0x13f0

bpf_int_jit_compile+0x1257/0x13f0

? arch_prepare_bpf_dispatcher+0xd0/0xd0

? rcu_read_lock_sched_held+0x43/0x70

bpf_prog_select_runtime+0x3e8/0x640

? bpf_obj_name_cpy+0x149/0x1b0

bpf_prog_load+0x102f/0x2220

? __bpf_prog_put.constprop.0+0x220/0x220

? find_held_lock+0x2c/0x110

? __might_fault+0xd6/0x180

? lock_downgrade+0x6e0/0x6e0

? lock_is_held_type+0xa6/0x120

? __might_fault+0x147/0x180

__sys_bpf+0x137b/0x6070

? bpf_perf_link_attach+0x530/0x530

? new_sync_read+0x600/0x600

? __fget_files+0x255/0x450

? lock_downgrade+0x6e0/0x6e0

? fput+0x30/0x1a0

? ksys_write+0x1a8/0x260

__x64_sys_bpf+0x7a/0xc0

? syscall_enter_from_user_mode+0x21/0x70

do_syscall_64+0x3b/0x90

entry_SYSCALL_64_after_hwframe+0x63/0xcd

RIP: 0033:0x7f917c4e2c2d

The problem here is that a range of tnum_range(0, map->max_entries - 1) has

limited ability to represent the concrete tight range with the tnum as the

set of resulting states from value + mask can result in a superset of the

actual intended range, and as such a tnum_in(range, reg->var_off) check may

yield true when it shouldn't, for example tnum_range(0, 2) would result in

00XX -> v = 0000, m = 0011 such that the intended set of {0, 1, 2} is here

represented by a less precise superset of {0, 1, 2, 3}. As the register is

known const scalar, really just use the concrete reg->var_off.value for the

upper index check.