[PATCH bpf] bpf: add check for invalid name in btf_name_valid_section()

[Jeongjun Park <aha310510@gmail.com>]

If the length of the name string is 1 and the value of name[0] is NULL 
byte, an OOB vulnerability occurs in btf_name_valid_section() and the 
return value is true, so the invalid name passes the check. 

To solve this, you need to check if the first position is NULL byte.

Fixes: bd70a8fb7ca4 ("bpf: Allow all printable characters in BTF DATASEC names")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 kernel/bpf/btf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 520f49f422fe..5c24ea1a65a4 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -823,6 +823,9 @@ static bool btf_name_valid_section(const struct btf *btf, u32 offset)
 	const char *src = btf_str_by_offset(btf, offset);
 	const char *src_limit;
 
+	if (!*src)
+		return false;
+
 	/* set a limit on identifier length */
 	src_limit = src + KSYM_NAME_LEN;
 	src++;
--