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bpf: verifier: Do not extract constant map keys for irrelevant maps

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Previously, we were trying to extract constant map keys for all
bpf_map_lookup_elem(), regardless of map type. This is an issue if the
map has a u64 key and the value is very high, as it can be interpreted
as a negative signed value. This in turn is treated as an error value by
check_func_arg() which causes a valid program to be incorrectly
rejected.

Fix by only extracting constant map keys for relevant maps. This fix
works because nullness elision is only allowed for {PERCPU_}ARRAY maps,
and keys for these are within u32 range. See next commit for an example
via selftest.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Reported-by: Ilya Leoshkevich <iii@linux.ibm.com>
Tested-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Link: https://lore.kernel.org/r/aa868b642b026ff87ba6105ea151bc8693b35932.1738689872.git.dxu@dxuuu.xyz
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Xu 2025-02-04 10:25:16 -07:00 • committed by Alexei Starovoitov
parent 517e8a7835
commit 884c3a18da
1 changed files with 7 additions and 3 deletions
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10
kernel/bpf/verifier.c
View file

@ -9206,6 +9206,8 @@ static s64 get_constant_map_key(struct bpf_verifier_env *env,
return reg->var_off.value;
}
static bool can_elide_value_nullness(enum bpf_map_type type);
static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
struct bpf_call_arg_meta *meta,
const struct bpf_func_proto *fn,
@ -9354,9 +9356,11 @@ skip_type_check:
err = check_helper_mem_access(env, regno, key_size, BPF_READ, false, NULL);
if (err)
return err;
meta->const_map_key = get_constant_map_key(env, reg, key_size);
if (meta->const_map_key < 0 && meta->const_map_key != -EOPNOTSUPP)
return meta->const_map_key;
if (can_elide_value_nullness(meta->map_ptr->map_type)) {
meta->const_map_key = get_constant_map_key(env, reg, key_size);
if (meta->const_map_key < 0 && meta->const_map_key != -EOPNOTSUPP)
return meta->const_map_key;
}
break;
case ARG_PTR_TO_MAP_VALUE:
if (type_may_be_null(arg_type) && register_is_null(reg))