Currently key_size of hashtab is limited to MAX_BPF_STACK.
As the key of hashtab can also be a value from a per cpu map it can be
larger than MAX_BPF_STACK.
The use-case for this patch originates to implement allow/disallow
lists for files and file paths. The maximum length of file paths is
defined by PATH_MAX with 4096 chars including nul.
This limit exceeds MAX_BPF_STACK.
Changelog:
v3:
- Rebase
v2:
- Add a test for bpf side
Signed-off-by: Florian Lehner <dev@xxxxxxxxxxx>
---
kernel/bpf/hashtab.c | 16 +++----
.../selftests/bpf/prog_tests/hash_large_key.c | 28 ++++++++++++
.../selftests/bpf/progs/test_hash_large_key.c | 45 +++++++++++++++++++
tools/testing/selftests/bpf/test_maps.c | 2 +-
4 files changed, 79 insertions(+), 12 deletions(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/hash_large_key.c
create mode 100644 tools/testing/selftests/bpf/progs/test_hash_large_key.c
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 1815e97d4c9c..10097d6bcc35 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -390,17 +390,11 @@ static int htab_map_alloc_check(union bpf_attr *attr)
attr->value_size == 0)
return -EINVAL;
- if (attr->key_size > MAX_BPF_STACK)
- /* eBPF programs initialize keys on stack, so they cannot be
- * larger than max stack size
- */
- return -E2BIG;
-
- if (attr->value_size >= KMALLOC_MAX_SIZE -
- MAX_BPF_STACK - sizeof(struct htab_elem))
- /* if value_size is bigger, the user space won't be able to
- * access the elements via bpf syscall. This check also makes
- * sure that the elem_size doesn't overflow and it's
+ if ((attr->key_size + attr->value_size) >= KMALLOC_MAX_SIZE -
+ sizeof(struct htab_elem))
+ /* if key_size + value_size is bigger, the user space won't be
+ * able to access the elements via bpf syscall. This check
+ * also makes sure that the elem_size doesn't overflow and it's
* kmalloc-able later in htab_map_update_elem()
*/
return -E2BIG;
diff --git a/tools/testing/selftests/bpf/prog_tests/hash_large_key.c b/tools/testing/selftests/bpf/prog_tests/hash_large_key.c
new file mode 100644
index 000000000000..962f56060b76
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/hash_large_key.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Florian Lehner
+
+#include <test_progs.h>
+
+void test_hash_large_key(void)
+{
+ const char *file = "./test_hash_large_key.o";
+ int prog_fd, map_fd[2];
+ struct bpf_object *obj = NULL;
+ int err = 0;
+
+ err = bpf_prog_load(file, BPF_PROG_TYPE_CGROUP_SKB, &obj, &prog_fd);
+ if (CHECK_FAIL(err)) {
+ printf("test_hash_large_key: bpf_prog_load errno %d", errno);
+ goto close_prog;
+ }
+
+ map_fd[0] = bpf_find_map(__func__, obj, "hash_map");
+ if (CHECK_FAIL(map_fd[0] < 0))
+ goto close_prog;
+ map_fd[1] = bpf_find_map(__func__, obj, "key_map");
+ if (CHECK_FAIL(map_fd[1] < 0))
+ goto close_prog;
+
+close_prog:
+ bpf_object__close(obj);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_hash_large_key.c b/tools/testing/selftests/bpf/progs/test_hash_large_key.c
new file mode 100644
index 000000000000..622ee73a4572
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_hash_large_key.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Florian Lehner
+
+#include <linux/bpf.h>
+#include <linux/version.h>
+#include <bpf/bpf_helpers.h>
+
+struct bigelement {
+ int a;
+ char b[4096];
+ long long c;
+};
+
+struct {
+ __uint(type, BPF_MAP_TYPE_HASH);
+ __uint(max_entries, 1);
+ __type(key, struct bigelement);
+ __type(value, __u32);
+} hash_map SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+ __uint(max_entries, 1);
+ __type(key, __u32);
+ __type(value, struct bigelement);
+} key_map SEC(".maps");
+
+SEC("hash_large_key_demo")
+int bpf_hash_large_key_test(struct __sk_buf *skb)
+{
+ int zero = 0, err = 1, value = 42;
+ struct bigelement *key;
+
+ key = bpf_map_lookup_elem(&key_map, &zero);
+ if (!key)
+ goto err;
+
+ if (bpf_map_update_elem(&hash_map, key, &value, BPF_ANY))
+ goto err;
+ err = 0;
+err:
+ return err;
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/test_maps.c b/tools/testing/selftests/bpf/test_maps.c
index 0d92ebcb335d..17fe19a2114d 100644
--- a/tools/testing/selftests/bpf/test_maps.c
+++ b/tools/testing/selftests/bpf/test_maps.c
@@ -1225,7 +1225,7 @@ static void test_map_large(void)
{
struct bigkey {
int a;
- char b[116];
+ char b[4096];
long long c;
} key;
int fd, i, value;
--
2.26.2
