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    Subject[PATCH 5.10 86/86] bpf: Dont use tnum_range on array range checking for poke descriptors
    Date
    From: Daniel Borkmann <daniel@iogearbox.net>

    commit a657182a5c5150cdfacb6640aad1d2712571a409 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    kernel/bpf/verifier.c | 10 ++++------
    1 file changed, 4 insertions(+), 6 deletions(-)

    --- a/kernel/bpf/verifier.c
    +++ b/kernel/bpf/verifier.c
    @@ -5282,8 +5282,7 @@ record_func_key(struct bpf_verifier_env
    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)
    @@ -5293,10 +5292,11 @@ record_func_key(struct bpf_verifier_env
    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;
    }
    @@ -5304,8 +5304,6 @@ record_func_key(struct bpf_verifier_env
    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) &&

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