CVE-2021-47300

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

---truncated---