bpf: Introduce bpf_sysctl_get_name helper

Add bpf_sysctl_get_name() helper to copy sysctl name (/proc/sys/ entry)
into provided by BPF_PROG_TYPE_CGROUP_SYSCTL program buffer.

By default full name (w/o /proc/sys/) is copied, e.g. "net/ipv4/tcp_mem".

If BPF_F_SYSCTL_BASE_NAME flag is set, only base name will be copied,
e.g. "tcp_mem".

Documentation for the new helper is provided in bpf.h UAPI.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 69 insertions, 1 deletions

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 610491b5f0aa..a68387043244 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -14,6 +14,7 @@
 #include <linux/filter.h>
 #include <linux/slab.h>
 #include <linux/sysctl.h>
+#include <linux/string.h>
 #include <linux/bpf.h>
 #include <linux/bpf-cgroup.h>
 #include <net/sock.h>
@@ -806,10 +807,77 @@ int __cgroup_bpf_run_filter_sysctl(struct ctl_table_header *head,
 }
 EXPORT_SYMBOL(__cgroup_bpf_run_filter_sysctl);
 
+static ssize_t sysctl_cpy_dir(const struct ctl_dir *dir, char **bufp,
+                              size_t *lenp)
+{
+        ssize_t tmp_ret = 0, ret;
+
+        if (dir->header.parent) {
+                tmp_ret = sysctl_cpy_dir(dir->header.parent, bufp, lenp);
+                if (tmp_ret < 0)
+                        return tmp_ret;
+        }
+
+        ret = strscpy(*bufp, dir->header.ctl_table[0].procname, *lenp);
+        if (ret < 0)
+                return ret;
+        *bufp += ret;
+        *lenp -= ret;
+        ret += tmp_ret;
+
+        /* Avoid leading slash. */
+        if (!ret)
+                return ret;
+
+        tmp_ret = strscpy(*bufp, "/", *lenp);
+        if (tmp_ret < 0)
+                return tmp_ret;
+        *bufp += tmp_ret;
+        *lenp -= tmp_ret;
+
+        return ret + tmp_ret;
+}
+
+BPF_CALL_4(bpf_sysctl_get_name, struct bpf_sysctl_kern *, ctx, char *, buf,
+           size_t, buf_len, u64, flags)
+{
+        ssize_t tmp_ret = 0, ret;
+
+        if (!buf)
+                return -EINVAL;
+
+        if (!(flags & BPF_F_SYSCTL_BASE_NAME)) {
+                if (!ctx->head)
+                        return -EINVAL;
+                tmp_ret = sysctl_cpy_dir(ctx->head->parent, &buf, &buf_len);
+                if (tmp_ret < 0)
+                        return tmp_ret;
+        }
+
+        ret = strscpy(buf, ctx->table->procname, buf_len);
+
+        return ret < 0 ? ret : tmp_ret + ret;
+}
+
+static const struct bpf_func_proto bpf_sysctl_get_name_proto = {
+        .func           = bpf_sysctl_get_name,
+        .gpl_only       = false,
+        .ret_type       = RET_INTEGER,
+        .arg1_type      = ARG_PTR_TO_CTX,
+        .arg2_type      = ARG_PTR_TO_MEM,
+        .arg3_type      = ARG_CONST_SIZE,
+        .arg4_type      = ARG_ANYTHING,
+};
+
 static const struct bpf_func_proto *
 sysctl_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
-        return cgroup_base_func_proto(func_id, prog);
+        switch (func_id) {
+        case BPF_FUNC_sysctl_get_name:
+                return &bpf_sysctl_get_name_proto;
+        default:
+                return cgroup_base_func_proto(func_id, prog);
+        }
 }
 
 static bool sysctl_is_valid_access(int off, int size, enum bpf_access_type type,