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bpf/btf: Accept function names that contain dots

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When building a kernel with LLVM=1, LLVM_IAS=0 and CONFIG_KASAN=y, LLVM
leaves DWARF tags for the "asan.module_ctor" & co symbols. In turn,
pahole creates BTF_KIND_FUNC entries for these and this makes the BTF
metadata validation fail because they contain a dot.

In a dramatic turn of event, this BTF verification failure can cause
the netfilter_bpf initialization to fail, causing netfilter_core to
free the netfilter_helper hashmap and netfilter_ftp to trigger a
use-after-free. The risk of u-a-f in netfilter will be addressed
separately but the existence of "asan.module_ctor" debug info under some
build conditions sounds like a good enough reason to accept functions
that contain dots in BTF.

Although using only LLVM=1 is the recommended way to compile clang-based
kernels, users can certainly do LLVM=1, LLVM_IAS=0 as well and we still
try to support that combination according to Nick. To clarify:

  - > v5.10 kernel, LLVM=1 (LLVM_IAS=0 is not the default) is recommended,
    but user can still have LLVM=1, LLVM_IAS=0 to trigger the issue

  - <= 5.10 kernel, LLVM=1 (LLVM_IAS=0 is the default) is recommended in
    which case GNU as will be used

Fixes: 1dc9285184 ("bpf: kernel side support for BTF Var and DataSec")
Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Cc: Yonghong Song <yhs@meta.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/bpf/20230615145607.3469985-1-revest@chromium.org
This commit is contained in:
Florent Revest 2023-06-15 16:56:07 +02:00 committed by Daniel Borkmann
parent b78b34c604
commit 9724160b39
1 changed files with 8 additions and 12 deletions
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20
kernel/bpf/btf.c
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@ -744,13 +744,12 @@ static bool btf_name_offset_valid(const struct btf *btf, u32 offset)
return offset < btf->hdr.str_len;
}
static bool __btf_name_char_ok(char c, bool first, bool dot_ok)
static bool __btf_name_char_ok(char c, bool first)
{
if ((first ? !isalpha(c) :
!isalnum(c)) &&
c != '_' &&
((c == '.' && !dot_ok) ||
c != '.'))
c != '.')
return false;
return true;
}
@ -767,20 +766,20 @@ static const char *btf_str_by_offset(const struct btf *btf, u32 offset)
return NULL;
}
static bool __btf_name_valid(const struct btf *btf, u32 offset, bool dot_ok)
static bool __btf_name_valid(const struct btf *btf, u32 offset)
{
/* offset must be valid */
const char *src = btf_str_by_offset(btf, offset);
const char *src_limit;
if (!__btf_name_char_ok(*src, true, dot_ok))
if (!__btf_name_char_ok(*src, true))
return false;
/* set a limit on identifier length */
src_limit = src + KSYM_NAME_LEN;
src++;
while (*src && src < src_limit) {
if (!__btf_name_char_ok(*src, false, dot_ok))
if (!__btf_name_char_ok(*src, false))
return false;
src++;
}
@ -788,17 +787,14 @@ static bool __btf_name_valid(const struct btf *btf, u32 offset, bool dot_ok)
return !*src;
}
/* Only C-style identifier is permitted. This can be relaxed if
* necessary.
*/
static bool btf_name_valid_identifier(const struct btf *btf, u32 offset)
{
return __btf_name_valid(btf, offset, false);
return __btf_name_valid(btf, offset);
}
static bool btf_name_valid_section(const struct btf *btf, u32 offset)
{
return __btf_name_valid(btf, offset, true);
return __btf_name_valid(btf, offset);
}
static const char *__btf_name_by_offset(const struct btf *btf, u32 offset)
@ -4422,7 +4418,7 @@ static s32 btf_var_check_meta(struct btf_verifier_env *env,
}
if (!t->name_off ||
!__btf_name_valid(env->btf, t->name_off, true)) {
!__btf_name_valid(env->btf, t->name_off)) {
btf_verifier_log_type(env, t, "Invalid name");
return -EINVAL;
}