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—