This allows user to push data into a msg using sk_msg program types. The format is as follows, bpf_msg_push_data(msg, offset, len, flags) this will insert 'len' bytes at offset 'offset'. For example to prepend 10 bytes at the front of the message the user can, bpf_msg_push_data(msg, 0, 10, 0); This will invalidate data bounds so BPF user will have to then recheck data bounds after calling this. After this the msg size will have been updated and the user is free to write into the added bytes. We allow any offset/len as long as it is within the (data, data_end) range. However, a copy will be required if the ring is full and its possible for the helper to fail with ENOMEM or EINVAL errors which need to be handled by the BPF program. This can be used similar to XDP metadata to pass data between sk_msg layer and lower layers.
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| @@ -2240,6 +2240,23 @@ union bpf_attr { · 2239 unmodified lines | ||
| 2240 | 2240 | * pointer that was returned from bpf_sk_lookup_xxx\ (). |
| 2241 | 2241 | * Return |
| 2242 | 2242 | * 0 on success, or a negative error in case of failure. |
| 2243 | + * | |
| 2244 | + * int bpf_msg_push_data(struct sk_buff *skb, u32 start, u32 len, u64 flags) | |
| 2245 | + * Description | |
| 2246 | + * For socket policies, insert *len* bytes into msg at offset | |
| 2247 | + * *start*. | |
| 2248 | + * | |
| 2249 | + * If a program of type **BPF_PROG_TYPE_SK_MSG** is run on a | |
| 2250 | + * *msg* it may want to insert metadata or options into the msg. | |
| 2251 | + * This can later be read and used by any of the lower layer BPF | |
| 2252 | + * hooks. | |
| 2253 | + * | |
| 2254 | + * This helper may fail if under memory pressure (a malloc | |
| 2255 | + * fails) in these cases BPF programs will get an appropriate | |
| 2256 | + * error and BPF programs will need to handle them. | |
| 2257 | + * | |
| 2258 | + * Return | |
| 2259 | + * 0 on success, or a negative error in case of failure. | |
| 2243 | 2260 | */ |
| 2244 | 2261 | #define __BPF_FUNC_MAPPER(FN) \ |
| 2245 | 2262 | FN(unspec), \ |
| @@ -2331,7 +2348,8 @@ union bpf_attr { · 85 unmodified lines | ||
| 2331 | 2348 | FN(sk_release), \ |
| 2332 | 2349 | FN(map_push_elem), \ |
| 2333 | 2350 | FN(map_pop_elem), \ |
| 2334 | − FN(map_peek_elem), | |
| 2351 | + FN(map_peek_elem), \ | |
| 2352 | + FN(msg_push_data), | |
| 2335 | 2353 | |
| 2336 | 2354 | /* integer value in 'imm' field of BPF_CALL instruction selects which helper |
| 2337 | 2355 | * function eBPF program intends to call |