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bpf: verifier: permit non-zero returns from async callbacks

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The verifier currently enforces a zero return value for all async
callbacks—a constraint originally introduced for bpf_timer. That
restriction is too narrow for other async use cases.

Relax the rule by allowing non-zero return codes from async callbacks in
general, while preserving the zero-return requirement for bpf_timer to
maintain its existing semantics.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250923112404.668720-5-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Mykyta Yatsenko 2025-09-23 12:23:59 +01:00 committed by Alexei Starovoitov
parent acc3a0d250
commit d2699bdb6e
1 changed files with 2 additions and 3 deletions
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5
kernel/bpf/verifier.c
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@ -10789,7 +10789,7 @@ static int set_timer_callback_state(struct bpf_verifier_env *env,
__mark_reg_not_init(env, &callee->regs[BPF_REG_4]);
__mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
callee->in_async_callback_fn = true;
callee->callback_ret_range = retval_range(0, 1);
callee->callback_ret_range = retval_range(0, 0);
return 0;
}
@ -17073,9 +17073,8 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
}
if (frame->in_async_callback_fn) {
/* enforce return zero from async callbacks like timer */
exit_ctx = "At async callback return";
range = retval_range(0, 0);
range = frame->callback_ret_range;
goto enforce_retval;
}