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bpf: Silence a warning in btf_type_id_size()

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syzbot reported a warning in [1] with the following stacktrace:
  WARNING: CPU: 0 PID: 5005 at kernel/bpf/btf.c:1988 btf_type_id_size+0x2d9/0x9d0 kernel/bpf/btf.c:1988
  ...
  RIP: 0010:btf_type_id_size+0x2d9/0x9d0 kernel/bpf/btf.c:1988
  ...
  Call Trace:
   <TASK>
   map_check_btf kernel/bpf/syscall.c:1024 [inline]
   map_create+0x1157/0x1860 kernel/bpf/syscall.c:1198
   __sys_bpf+0x127f/0x5420 kernel/bpf/syscall.c:5040
   __do_sys_bpf kernel/bpf/syscall.c:5162 [inline]
   __se_sys_bpf kernel/bpf/syscall.c:5160 [inline]
   __x64_sys_bpf+0x79/0xc0 kernel/bpf/syscall.c:5160
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x63/0xcd

With the following btf
  [1] DECL_TAG 'a' type_id=4 component_idx=-1
  [2] PTR '(anon)' type_id=0
  [3] TYPE_TAG 'a' type_id=2
  [4] VAR 'a' type_id=3, linkage=static
and when the bpf_attr.btf_key_type_id = 1 (DECL_TAG),
the following WARN_ON_ONCE in btf_type_id_size() is triggered:
  if (WARN_ON_ONCE(!btf_type_is_modifier(size_type) &&
                   !btf_type_is_var(size_type)))
          return NULL;

Note that 'return NULL' is the correct behavior as we don't want
a DECL_TAG type to be used as a btf_{key,value}_type_id even
for the case like 'DECL_TAG -> STRUCT'. So there
is no correctness issue here, we just want to silence warning.

To silence the warning, I added DECL_TAG as one of kinds in
btf_type_nosize() which will cause btf_type_id_size() returning
NULL earlier without the warning.

  [1] https://lore.kernel.org/bpf/000000000000e0df8d05fc75ba86@google.com/

Reported-by: syzbot+958967f249155967d42a@syzkaller.appspotmail.com
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20230530205029.264910-1-yhs@fb.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
This commit is contained in:
Yonghong Song 2023-05-30 13:50:29 -07:00 committed by Martin KaFai Lau
parent bc590b4754
commit e6c2f594ed
1 changed files with 12 additions and 11 deletions
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23
kernel/bpf/btf.c
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@ -492,17 +492,6 @@ static bool btf_type_is_fwd(const struct btf_type *t)
return BTF_INFO_KIND(t->info) == BTF_KIND_FWD;
}
static bool btf_type_nosize(const struct btf_type *t)
{
return btf_type_is_void(t) || btf_type_is_fwd(t) ||
btf_type_is_func(t) || btf_type_is_func_proto(t);
}
static bool btf_type_nosize_or_null(const struct btf_type *t)
{
return !t || btf_type_nosize(t);
}
static bool btf_type_is_datasec(const struct btf_type *t)
{
return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
@ -513,6 +502,18 @@ static bool btf_type_is_decl_tag(const struct btf_type *t)
return BTF_INFO_KIND(t->info) == BTF_KIND_DECL_TAG;
}
static bool btf_type_nosize(const struct btf_type *t)
{
return btf_type_is_void(t) || btf_type_is_fwd(t) ||
btf_type_is_func(t) || btf_type_is_func_proto(t) ||
btf_type_is_decl_tag(t);
}
static bool btf_type_nosize_or_null(const struct btf_type *t)
{
return !t || btf_type_nosize(t);
}
static bool btf_type_is_decl_tag_target(const struct btf_type *t)
{
return btf_type_is_func(t) || btf_type_is_struct(t) ||