bpf: Silence a warning in btf_type_id_size()

yonghong-song · gregkh · commit 7c4f5ab63e79 · 2023-07-27T08:56:49.000+02:00
[ Upstream commit e6c2f59 ] 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> Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
@@ -485,25 +485,26 @@ 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)
+static bool btf_type_is_datasec(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);
+	return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
 }
 
-static bool btf_type_nosize_or_null(const struct btf_type *t)
+static bool btf_type_is_decl_tag(const struct btf_type *t)
 {
-	return !t || btf_type_nosize(t);
+	return BTF_INFO_KIND(t->info) == BTF_KIND_DECL_TAG;
 }
 
-static bool btf_type_is_datasec(const struct btf_type *t)
+static bool btf_type_nosize(const struct btf_type *t)
 {
-	return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
+	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_is_decl_tag(const struct btf_type *t)
+static bool btf_type_nosize_or_null(const struct btf_type *t)
 {
-	return BTF_INFO_KIND(t->info) == BTF_KIND_DECL_TAG;
+	return !t || btf_type_nosize(t);
 }
 
 static bool btf_type_is_decl_tag_target(const struct btf_type *t)

Original file line number	Diff line number	Diff line change
`@@ -485,25 +485,26 @@ static bool btf_type_is_fwd(const struct btf_type *t)`
`485`	`485`	`return BTF_INFO_KIND(t->info) == BTF_KIND_FWD;`
`486`	`486`	`}`
`487`	`487`
`488`		`-static bool btf_type_nosize(const struct btf_type *t)`
	`488`	`+static bool btf_type_is_datasec(const struct btf_type *t)`
`489`	`489`	`{`
`490`		`- return btf_type_is_void(t) \|\| btf_type_is_fwd(t) \|\|`
`491`		`- btf_type_is_func(t) \|\| btf_type_is_func_proto(t);`
	`490`	`+ return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;`
`492`	`491`	`}`
`493`	`492`
`494`		`-static bool btf_type_nosize_or_null(const struct btf_type *t)`
	`493`	`+static bool btf_type_is_decl_tag(const struct btf_type *t)`
`495`	`494`	`{`
`496`		`- return !t \|\| btf_type_nosize(t);`
	`495`	`+ return BTF_INFO_KIND(t->info) == BTF_KIND_DECL_TAG;`
`497`	`496`	`}`
`498`	`497`
`499`		`-static bool btf_type_is_datasec(const struct btf_type *t)`
	`498`	`+static bool btf_type_nosize(const struct btf_type *t)`
`500`	`499`	`{`
`501`		`- return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;`
	`500`	`+ return btf_type_is_void(t) \|\| btf_type_is_fwd(t) \|\|`
	`501`	`+ btf_type_is_func(t) \|\| btf_type_is_func_proto(t) \|\|`
	`502`	`+ btf_type_is_decl_tag(t);`
`502`	`503`	`}`
`503`	`504`
`504`		`-static bool btf_type_is_decl_tag(const struct btf_type *t)`
	`505`	`+static bool btf_type_nosize_or_null(const struct btf_type *t)`
`505`	`506`	`{`
`506`		`- return BTF_INFO_KIND(t->info) == BTF_KIND_DECL_TAG;`
	`507`	`+ return !t \|\| btf_type_nosize(t);`
`507`	`508`	`}`
`508`	`509`
`509`	`510`	`static bool btf_type_is_decl_tag_target(const struct btf_type *t)`