Subject: CVE-2021-47300: bpf: Fix tail_call_reachable rejection for interpreter when jit failed

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

bpf: Fix tail_call_reachable rejection for interpreter when jit failed

During testing of f263a81451c1 ("bpf: Track subprog poke descriptors correctly
and fix use-after-free") under various failure conditions, for example, when
jit_subprogs() fails and tries to clean up the program to be run under the
interpreter, we ran into the following freeze:

  [...]
  #127/8 tailcall_bpf2bpf_3:FAIL
  [...]
  [   92.041251] BUG: KASAN: slab-out-of-bounds in ___bpf_prog_run+0x1b9d/0x2e20
  [   92.042408] Read of size 8 at addr ffff88800da67f68 by task test_progs/682
  [   92.043707]
  [   92.044030] CPU: 1 PID: 682 Comm: test_progs Tainted: G   O   5.13.0-53301-ge6c08cb33a30-dirty #87
  [   92.045542] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
  [   92.046785] Call Trace:
  [   92.047171]  ? __bpf_prog_run_args64+0xc0/0xc0
  [   92.047773]  ? __bpf_prog_run_args32+0x8b/0xb0
  [   92.048389]  ? __bpf_prog_run_args64+0xc0/0xc0
  [   92.049019]  ? ktime_get+0x117/0x130
  [...] // few hundred [similar] lines more
  [   92.659025]  ? ktime_get+0x117/0x130
  [   92.659845]  ? __bpf_prog_run_args64+0xc0/0xc0
  [   92.660738]  ? __bpf_prog_run_args32+0x8b/0xb0
  [   92.661528]  ? __bpf_prog_run_args64+0xc0/0xc0
  [   92.662378]  ? print_usage_bug+0x50/0x50
  [   92.663221]  ? print_usage_bug+0x50/0x50
  [   92.664077]  ? bpf_ksym_find+0x9c/0xe0
  [   92.664887]  ? ktime_get+0x117/0x130
  [   92.665624]  ? kernel_text_address+0xf5/0x100
  [   92.666529]  ? __kernel_text_address+0xe/0x30
  [   92.667725]  ? unwind_get_return_address+0x2f/0x50
  [   92.668854]  ? ___bpf_prog_run+0x15d4/0x2e20
  [   92.670185]  ? ktime_get+0x117/0x130
  [   92.671130]  ? __bpf_prog_run_args64+0xc0/0xc0
  [   92.672020]  ? __bpf_prog_run_args32+0x8b/0xb0
  [   92.672860]  ? __bpf_prog_run_args64+0xc0/0xc0
  [   92.675159]  ? ktime_get+0x117/0x130
  [   92.677074]  ? lock_is_held_type+0xd5/0x130
  [   92.678662]  ? ___bpf_prog_run+0x15d4/0x2e20
  [   92.680046]  ? ktime_get+0x117/0x130
  [   92.681285]  ? __bpf_prog_run32+0x6b/0x90
  [   92.682601]  ? __bpf_prog_run64+0x90/0x90
  [   92.683636]  ? lock_downgrade+0x370/0x370
  [   92.684647]  ? mark_held_locks+0x44/0x90
  [   92.685652]  ? ktime_get+0x117/0x130
  [   92.686752]  ? lockdep_hardirqs_on+0x79/0x100
  [   92.688004]  ? ktime_get+0x117/0x130
  [   92.688573]  ? __cant_migrate+0x2b/0x80
  [   92.689192]  ? bpf_test_run+0x2f4/0x510
  [   92.689869]  ? bpf_test_timer_continue+0x1c0/0x1c0
  [   92.690856]  ? rcu_read_lock_bh_held+0x90/0x90
  [   92.691506]  ? __kasan_slab_alloc+0x61/0x80
  [   92.692128]  ? eth_type_trans+0x128/0x240
  [   92.692737]  ? __build_skb+0x46/0x50
  [   92.693252]  ? bpf_prog_test_run_skb+0x65e/0xc50
  [   92.693954]  ? bpf_prog_test_run_raw_tp+0x2d0/0x2d0
  [   92.694639]  ? __fget_light+0xa1/0x100
  [   92.695162]  ? bpf_prog_inc+0x23/0x30
  [   92.695685]  ? __sys_bpf+0xb40/0x2c80
  [   92.696324]  ? bpf_link_get_from_fd+0x90/0x90
  [   92.697150]  ? mark_held_locks+0x24/0x90
  [   92.698007]  ? lockdep_hardirqs_on_prepare+0x124/0x220
  [   92.699045]  ? finish_task_switch+0xe6/0x370
  [   92.700072]  ? lockdep_hardirqs_on+0x79/0x100
  [   92.701233]  ? finish_task_switch+0x11d/0x370
  [   92.702264]  ? __switch_to+0x2c0/0x740
  [   92.703148]  ? mark_held_locks+0x24/0x90
  [   92.704155]  ? __x64_sys_bpf+0x45/0x50
  [   92.705146]  ? do_syscall_64+0x35/0x80
  [   92.706953]  ? entry_SYSCALL_64_after_hwframe+0x44/0xae
  [...]

Turns out that the program rejection from e411901c0b77 ("bpf: allow for tailcalls
in BPF subprograms for x64 JIT") is buggy since env->prog->aux->tail_call_reachable
is never true. Commit ebf7d1f508a7 ("bpf, x64: rework pro/epilogue and tailcall
handling in JIT") added a tracker into check_max_stack_depth() which propagates
the tail_call_reachable condition throughout the subprograms. This info is then
assigned to the subprogram's func[i]->aux->tail_call_reachable. However, in the
case of the rejection check upon JIT failure, env->prog->aux->tail_call_reachable
is used. func[0]->aux->tail_call_reachable which represents the main program's
information did not propagate this to the outer env->prog->aux, though. Add this
propagation into check_max_stack_depth() where it needs to belong so that the
check can be done reliably.

The Linux kernel CVE team has assigned CVE-2021-47300 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.10 with commit e411901c0b77 and fixed in 5.10.54 with commit 39f1735c8107
	Issue introduced in 5.10 with commit e411901c0b77 and fixed in 5.13.6 with commit cbb086074dab
	Issue introduced in 5.10 with commit e411901c0b77 and fixed in 5.14 with commit 5dd0a6b8582f

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47300
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	kernel/bpf/verifier.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/39f1735c8107ef43a53c4daf82f330d880488d8f
	https://git.kernel.org/stable/c/cbb086074dab631ac43f8645cbac1d7b148e05c4
	https://git.kernel.org/stable/c/5dd0a6b8582ffbfa88351949d50eccd5b6694ade