On Mon, Sep 09, 2024 at 08:09:58PM -0300, Diogo Jahchan Koike wrote:

From: Yonghong Song yhs@fb.com

commit e6c2f594ed961273479505b42040782820190305 upstream.

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 (cherry picked from commit e6c2f594ed961273479505b42040782820190305) Signed-off-by: Diogo Jahchan Koike djahchankoike@gmail.com

---

kernel/bpf/btf.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 7582ec4fd413..2c58a6c3f978 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -466,10 +466,16 @@ static bool btf_type_is_fwd(const struct btf_type *t) return BTF_INFO_KIND(t->info) == BTF_KIND_FWD; } +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_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) @@ -492,11 +498,6 @@ static bool btf_type_is_datasec(const struct btf_type *t) return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC; } -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_is_decl_tag_target(const struct btf_type *t) { return btf_type_is_func(t) || btf_type_is_struct(t) || -- 2.43.0

Now queued up, thanks.

greg k-h