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bpf: Relax verifier recursion check.

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In the following bpf subprogram:
static int timer_cb(void *map, void *key, void *value)
{
    bpf_timer_set_callback(.., timer_cb);
}

the 'timer_cb' is a pointer to a function.
ld_imm64 insn is used to carry this pointer.
bpf_pseudo_func() returns true for such ld_imm64 insn.

Unlike bpf_for_each_map_elem() the bpf_timer_set_callback() is asynchronous.
Relax control flow check to allow such "recursion" that is seen as an infinite
loop by check_cfg(). The distinction between bpf_for_each_map_elem() the
bpf_timer_set_callback() is done in the follow up patch.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210715005417.78572-8-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2021-07-14 17:54:13 -07:00 committed by Daniel Borkmann
parent 40ec00abf1
commit 86fc6ee6e2
1 changed files with 6 additions and 2 deletions
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8
kernel/bpf/verifier.c
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@ -9463,8 +9463,12 @@ static int visit_func_call_insn(int t, int insn_cnt,
init_explored_state(env, t + 1);
if (visit_callee) {
init_explored_state(env, t);
ret = push_insn(t, t + insns[t].imm + 1, BRANCH,
env, false);
ret = push_insn(t, t + insns[t].imm + 1, BRANCH, env,
/* It's ok to allow recursion from CFG point of
* view. __check_func_call() will do the actual
* check.
*/
bpf_pseudo_func(insns + t));
}
return ret;
}