Re: [PATCH bpf] bpf: Sanitize the bpf_struct_ops tcp-cc name

On Fri, Mar 13, 2020 at 05:16:55PM -0700, Andrii Nakryiko wrote:

On Fri, Mar 13, 2020 at 4:37 PM Martin KaFai Lau [off-list ref] wrote:

quoted

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.

Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf")
Signed-off-by: Martin KaFai Lau <redacted>
---
 include/linux/bpf.h   |  1 +
 kernel/bpf/syscall.c  | 24 +++++++++++++-----------
 net/ipv4/bpf_tcp_ca.c |  7 ++-----
 3 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 49b1a70e12c8..212991f6f2a5 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -160,6 +160,7 @@ static inline void copy_map_value(struct bpf_map *map, void *dst, void *src)
 }
 void copy_map_value_locked(struct bpf_map *map, void *dst, void *src,
                           bool lock_src);
+int bpf_obj_name_cpy(char *dst, const char *src, unsigned int size);

 struct bpf_offload_dev;
 struct bpf_offloaded_map;

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0c7fb0d4836d..d2984bf362c2 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c

@@ -696,14 +696,14 @@ 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;

-       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 +712,11 @@ 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 - (end - size);

it's a rather convoluted way of writing (src - orig_src), maybe just
remember original src?

Sure. I can send v2.  Thanks for the review!

Either way not a big deal:

Acked-by: Andrii Nakryiko <redacted>

quoted

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