bpf: Add bpf_strncmp helper

The helper compares two strings: one string is a null-terminated
read-only string, and another string has const max storage size
but doesn't need to be null-terminated. It can be used to compare
file name in tracing or LSM program.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211210141652.877186-2-houtao1@huawei.com

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 0ceb54c..7a40022 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2163,6 +2163,7 @@ extern const struct bpf_func_proto bpf_sk_getsockopt_proto;
 extern const struct bpf_func_proto bpf_kallsyms_lookup_name_proto;
 extern const struct bpf_func_proto bpf_find_vma_proto;
 extern const struct bpf_func_proto bpf_loop_proto;
+extern const struct bpf_func_proto bpf_strncmp_proto;
 
 const struct bpf_func_proto *tracing_prog_func_proto(
   enum bpf_func_id func_id, const struct bpf_prog *prog);

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c268712..2820c77 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4983,6 +4983,16 @@ union bpf_attr {
  *     Return
  *             The number of loops performed, **-EINVAL** for invalid **flags**,
  *             **-E2BIG** if **nr_loops** exceeds the maximum number of loops.
+ *
+ * long bpf_strncmp(const char *s1, u32 s1_sz, const char *s2)
+ *     Description
+ *             Do strncmp() between **s1** and **s2**. **s1** doesn't need
+ *             to be null-terminated and **s1_sz** is the maximum storage
+ *             size of **s1**. **s2** must be a read-only string.
+ *     Return
+ *             An integer less than, equal to, or greater than zero
+ *             if the first **s1_sz** bytes of **s1** is found to be
+ *             less than, to match, or be greater than **s2**.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5167,6 +5177,7 @@ union bpf_attr {
        FN(kallsyms_lookup_name),       \
        FN(find_vma),                   \
        FN(loop),                       \
+       FN(strncmp),                    \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 19fecfe..8babae0 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -565,6 +565,20 @@ const struct bpf_func_proto bpf_strtoul_proto = {
 };
 #endif
 
+BPF_CALL_3(bpf_strncmp, const char *, s1, u32, s1_sz, const char *, s2)
+{
+       return strncmp(s1, s2, s1_sz);
+}
+
+const struct bpf_func_proto bpf_strncmp_proto = {
+       .func           = bpf_strncmp,
+       .gpl_only       = false,
+       .ret_type       = RET_INTEGER,
+       .arg1_type      = ARG_PTR_TO_MEM,
+       .arg2_type      = ARG_CONST_SIZE,
+       .arg3_type      = ARG_PTR_TO_CONST_STR,
+};
+
 BPF_CALL_4(bpf_get_ns_current_pid_tgid, u64, dev, u64, ino,
           struct bpf_pidns_info *, nsdata, u32, size)
 {
@@ -1378,6 +1392,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
                return &bpf_for_each_map_elem_proto;
        case BPF_FUNC_loop:
                return &bpf_loop_proto;
+       case BPF_FUNC_strncmp:
+               return &bpf_strncmp_proto;
        default:
                break;
        }

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c268712..2820c77 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4983,6 +4983,16 @@ union bpf_attr {
  *     Return
  *             The number of loops performed, **-EINVAL** for invalid **flags**,
  *             **-E2BIG** if **nr_loops** exceeds the maximum number of loops.
+ *
+ * long bpf_strncmp(const char *s1, u32 s1_sz, const char *s2)
+ *     Description
+ *             Do strncmp() between **s1** and **s2**. **s1** doesn't need
+ *             to be null-terminated and **s1_sz** is the maximum storage
+ *             size of **s1**. **s2** must be a read-only string.
+ *     Return
+ *             An integer less than, equal to, or greater than zero
+ *             if the first **s1_sz** bytes of **s1** is found to be
+ *             less than, to match, or be greater than **s2**.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5167,6 +5177,7 @@ union bpf_attr {
        FN(kallsyms_lookup_name),       \
        FN(find_vma),                   \
        FN(loop),                       \
+       FN(strncmp),                    \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper