bpf, arm64: Clear prog->jited_len along prog->jited

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

bpf, arm64: Clear prog->jited_len along prog->jited

syzbot reported an illegal copy_to_user() attempt

from bpf_prog_get_info_by_fd() [1]

There was no repro yet on this bug, but I think

that commit 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns")

is exposing a prior bug in bpf arm64.

bpf_prog_get_info_by_fd() looks at prog->jited_len

to determine if the JIT image can be copied out to user space.

My theory is that syzbot managed to get a prog where prog->jited_len

has been set to 43, while prog->bpf_func has ben cleared.

It is not clear why copy_to_user(uinsns, NULL, ulen) is triggering

this particular warning.

I thought find_vma_area(NULL) would not find a vm_struct.

As we do not hold vmap_area_lock spinlock, it might be possible

that the found vm_struct was garbage.

[1]

usercopy: Kernel memory exposure attempt detected from vmalloc (offset 792633534417210172, size 43)!

kernel BUG at mm/usercopy.c:101!

Internal error: Oops - BUG: 0 [#1] PREEMPT SMP

Modules linked in:

CPU: 0 PID: 25002 Comm: syz-executor.1 Not tainted 5.18.0-syzkaller-10139-g8291eaafed36 #0

Hardware name: linux,dummy-virt (DT)

pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)

pc : usercopy_abort+0x90/0x94 mm/usercopy.c:101

lr : usercopy_abort+0x90/0x94 mm/usercopy.c:89

sp : ffff80000b773a20

x29: ffff80000b773a30 x28: faff80000b745000 x27: ffff80000b773b48

x26: 0000000000000000 x25: 000000000000002b x24: 0000000000000000

x23: 00000000000000e0 x22: ffff80000b75db67 x21: 0000000000000001

x20: 000000000000002b x19: ffff80000b75db3c x18: 00000000fffffffd

x17: 2820636f6c6c616d x16: 76206d6f72662064 x15: 6574636574656420

x14: 74706d6574746120 x13: 2129333420657a69 x12: 73202c3237313031

x11: 3237313434333533 x10: 3336323937207465 x9 : 657275736f707865

x8 : ffff80000a30c550 x7 : ffff80000b773830 x6 : ffff80000b773830

x5 : 0000000000000000 x4 : ffff00007fbbaa10 x3 : 0000000000000000

x2 : 0000000000000000 x1 : f7ff000028fc0000 x0 : 0000000000000064

Call trace:

usercopy_abort+0x90/0x94 mm/usercopy.c:89

check_heap_object mm/usercopy.c:186 [inline]

__check_object_size mm/usercopy.c:252 [inline]

__check_object_size+0x198/0x36c mm/usercopy.c:214

check_object_size include/linux/thread_info.h:199 [inline]

check_copy_size include/linux/thread_info.h:235 [inline]

copy_to_user include/linux/uaccess.h:159 [inline]

bpf_prog_get_info_by_fd.isra.0+0xf14/0xfdc kernel/bpf/syscall.c:3993

bpf_obj_get_info_by_fd+0x12c/0x510 kernel/bpf/syscall.c:4253

__sys_bpf+0x900/0x2150 kernel/bpf/syscall.c:4956

__do_sys_bpf kernel/bpf/syscall.c:5021 [inline]

__se_sys_bpf kernel/bpf/syscall.c:5019 [inline]

__arm64_sys_bpf+0x28/0x40 kernel/bpf/syscall.c:5019

__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]

invoke_syscall+0x48/0x114 arch/arm64/kernel/syscall.c:52

el0_svc_common.constprop.0+0x44/0xec arch/arm64/kernel/syscall.c:142

do_el0_svc+0xa0/0xc0 arch/arm64/kernel/syscall.c:206

el0_svc+0x44/0xb0 arch/arm64/kernel/entry-common.c:624

el0t_64_sync_handler+0x1ac/0x1b0 arch/arm64/kernel/entry-common.c:642

el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:581

Code: aa0003e3 d00038c0 91248000 97fff65f (d4210000)