bpf: Sanitize the bpf_struct_ops tcp-cc name

The bpf_struct_ops tcp-cc name should be sanitized in order to
avoid problematic chars (e.g. whitespaces).

This patch reuses the bpf_obj_name_cpy() for accepting the same set
of characters in order to keep a consistent bpf programming experience.
A "size" param is added.  Also, the strlen is returned on success so
that the caller (like the bpf_tcp_ca here) can error out on empty name.
The existing callers of the bpf_obj_name_cpy() only need to change the
testing statement to "if (err < 0)".  For all these existing callers,
the err will be overwritten later, so no extra change is needed
for the new strlen return value.

v3:
  - reverse xmas tree style
v2:
  - Save the orig_src to avoid "end - size" (Andrii)

Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf")
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200314010209.1131542-1-kafai@fb.com

1 files changed, 14 insertions, 11 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0c7fb0d4836d..2857b7dda382 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -696,14 +696,15 @@ int bpf_get_file_flag(int flags)
 		   offsetof(union bpf_attr, CMD##_LAST_FIELD) - \
 		   sizeof(attr->CMD##_LAST_FIELD)) != NULL
 
-/* dst and src must have at least BPF_OBJ_NAME_LEN number of bytes.
- * Return 0 on success and < 0 on error.
+/* dst and src must have at least "size" number of bytes.
+ * Return strlen on success and < 0 on error.
  */
-static int bpf_obj_name_cpy(char *dst, const char *src)
+int bpf_obj_name_cpy(char *dst, const char *src, unsigned int size)
 {
-	const char *end = src + BPF_OBJ_NAME_LEN;
+	const char *end = src + size;
+	const char *orig_src = src;
 
-	memset(dst, 0, BPF_OBJ_NAME_LEN);
+	memset(dst, 0, size);
 	/* Copy all isalnum(), '_' and '.' chars. */
 	while (src < end && *src) {
 		if (!isalnum(*src) &&
@@ -712,11 +713,11 @@ static int bpf_obj_name_cpy(char *dst, const char *src)
 		*dst++ = *src++;
 	}
 
-	/* No '\0' found in BPF_OBJ_NAME_LEN number of bytes */
+	/* No '\0' found in "size" number of bytes */
 	if (src == end)
 		return -EINVAL;
 
-	return 0;
+	return src - orig_src;
 }
 
 int map_check_no_btf(const struct bpf_map *map,
@@ -810,8 +811,9 @@ static int map_create(union bpf_attr *attr)
 	if (IS_ERR(map))
 		return PTR_ERR(map);
 
-	err = bpf_obj_name_cpy(map->name, attr->map_name);
-	if (err)
+	err = bpf_obj_name_cpy(map->name, attr->map_name,
+			       sizeof(attr->map_name));
+	if (err < 0)
 		goto free_map;
 
 	atomic64_set(&map->refcnt, 1);
@@ -2098,8 +2100,9 @@ static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr)
 		goto free_prog;
 
 	prog->aux->load_time = ktime_get_boottime_ns();
-	err = bpf_obj_name_cpy(prog->aux->name, attr->prog_name);
-	if (err)
+	err = bpf_obj_name_cpy(prog->aux->name, attr->prog_name,
+			       sizeof(attr->prog_name));
+	if (err < 0)
 		goto free_prog;
 
 	/* run eBPF verifier */