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authorDaniel Borkmann <daniel@iogearbox.net>2022-08-25 23:26:47 +0200
committerAlexei Starovoitov <ast@kernel.org>2022-08-25 14:58:30 -0700
commita657182a5c5150cdfacb6640aad1d2712571a409 (patch)
tree02a3517d59fb986b4b6d34e829ce6d3293f68cd5 /kernel
parentcb15c7348737c6956652832832d0407f69b2aff3 (diff)
bpf: Don't use tnum_range on array range checking for poke descriptors
Hsin-Wei reported a KASAN splat triggered by their BPF runtime fuzzer which is based on a customized syzkaller: BUG: KASAN: slab-out-of-bounds in bpf_int_jit_compile+0x1257/0x13f0 Read of size 8 at addr ffff888004e90b58 by task syz-executor.0/1489 CPU: 1 PID: 1489 Comm: syz-executor.0 Not tainted 5.19.0 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x9c/0xc9 print_address_description.constprop.0+0x1f/0x1f0 ? bpf_int_jit_compile+0x1257/0x13f0 kasan_report.cold+0xeb/0x197 ? kvmalloc_node+0x170/0x200 ? bpf_int_jit_compile+0x1257/0x13f0 bpf_int_jit_compile+0x1257/0x13f0 ? arch_prepare_bpf_dispatcher+0xd0/0xd0 ? rcu_read_lock_sched_held+0x43/0x70 bpf_prog_select_runtime+0x3e8/0x640 ? bpf_obj_name_cpy+0x149/0x1b0 bpf_prog_load+0x102f/0x2220 ? __bpf_prog_put.constprop.0+0x220/0x220 ? find_held_lock+0x2c/0x110 ? __might_fault+0xd6/0x180 ? lock_downgrade+0x6e0/0x6e0 ? lock_is_held_type+0xa6/0x120 ? __might_fault+0x147/0x180 __sys_bpf+0x137b/0x6070 ? bpf_perf_link_attach+0x530/0x530 ? new_sync_read+0x600/0x600 ? __fget_files+0x255/0x450 ? lock_downgrade+0x6e0/0x6e0 ? fput+0x30/0x1a0 ? ksys_write+0x1a8/0x260 __x64_sys_bpf+0x7a/0xc0 ? syscall_enter_from_user_mode+0x21/0x70 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f917c4e2c2d The problem here is that a range of tnum_range(0, map->max_entries - 1) has limited ability to represent the concrete tight range with the tnum as the set of resulting states from value + mask can result in a superset of the actual intended range, and as such a tnum_in(range, reg->var_off) check may yield true when it shouldn't, for example tnum_range(0, 2) would result in 00XX -> v = 0000, m = 0011 such that the intended set of {0, 1, 2} is here represented by a less precise superset of {0, 1, 2, 3}. As the register is known const scalar, really just use the concrete reg->var_off.value for the upper index check. Fixes: d2e4c1e6c294 ("bpf: Constant map key tracking for prog array pokes") Reported-by: Hsin-Wei Hung <hsinweih@uci.edu> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Cc: Shung-Hsi Yu <shung-hsi.yu@suse.com> Acked-by: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/r/984b37f9fdf7ac36831d2137415a4a915744c1b6.1661462653.git.daniel@iogearbox.net Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/bpf/verifier.c10
1 files changed, 4 insertions, 6 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 30c6eebce146..3eadb14e090b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7033,8 +7033,7 @@ record_func_key(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
struct bpf_insn_aux_data *aux = &env->insn_aux_data[insn_idx];
struct bpf_reg_state *regs = cur_regs(env), *reg;
struct bpf_map *map = meta->map_ptr;
- struct tnum range;
- u64 val;
+ u64 val, max;
int err;
if (func_id != BPF_FUNC_tail_call)
@@ -7044,10 +7043,11 @@ record_func_key(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
return -EINVAL;
}
- range = tnum_range(0, map->max_entries - 1);
reg = &regs[BPF_REG_3];
+ val = reg->var_off.value;
+ max = map->max_entries;
- if (!register_is_const(reg) || !tnum_in(range, reg->var_off)) {
+ if (!(register_is_const(reg) && val < max)) {
bpf_map_key_store(aux, BPF_MAP_KEY_POISON);
return 0;
}
@@ -7055,8 +7055,6 @@ record_func_key(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
err = mark_chain_precision(env, BPF_REG_3);
if (err)
return err;
-
- val = reg->var_off.value;
if (bpf_map_key_unseen(aux))
bpf_map_key_store(aux, val);
else if (!bpf_map_key_poisoned(aux) &&