CVE-2022-49341 — bpf, arm64: Clear prog->jited_len along prog->jited

Affected: Linux

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: 0000000000000…

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CVE-2022-49341 — bpf, arm64: Clear prog->jited_len along prog->jited