6.1-stable review patch. If anyone has any objections, please let me know.
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From: David Vernet void@manifault.com
[ Upstream commit 829955981c557c7fc7416581c4cd68a8a0c28620 ]
The verifier, as part of check_return_code(), verifies that async callbacks such as from e.g. timers, will return 0. It does this by correctly checking that R0->var_off is in tnum_const(0), which effectively checks that it's in a range of 0. If this condition fails, however, it prints an error message which says that the value should have been in (0x0; 0x1). This results in possibly confusing output such as the following in which an async callback returns 1:
At async callback the register R0 has value (0x1; 0x0) should have been in (0x0; 0x1)
The fix is easy -- we should just pass the tnum_const(0) as the correct range to verbose_invalid_scalar(), which will then print the following:
At async callback the register R0 has value (0x1; 0x0) should have been in (0x0; 0x0)
Fixes: bfc6bb74e4f1 ("bpf: Implement verifier support for validation of async callbacks.") Signed-off-by: David Vernet void@manifault.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20231009161414.235829-1-void@manifault.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 3052680201e57..eb3f52be115d6 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10778,7 +10778,7 @@ static int check_return_code(struct bpf_verifier_env *env) struct tnum enforce_attach_type_range = tnum_unknown; const struct bpf_prog *prog = env->prog; struct bpf_reg_state *reg; - struct tnum range = tnum_range(0, 1); + struct tnum range = tnum_range(0, 1), const_0 = tnum_const(0); enum bpf_prog_type prog_type = resolve_prog_type(env->prog); int err; struct bpf_func_state *frame = env->cur_state->frame[0]; @@ -10826,8 +10826,8 @@ static int check_return_code(struct bpf_verifier_env *env) return -EINVAL; }
- if (!tnum_in(tnum_const(0), reg->var_off)) { - verbose_invalid_scalar(env, reg, &range, "async callback", "R0"); + if (!tnum_in(const_0, reg->var_off)) { + verbose_invalid_scalar(env, reg, &const_0, "async callback", "R0"); return -EINVAL; } return 0;