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Message-Id: <20201029201442.596690-1-dev@der-flo.net>
Date: Thu, 29 Oct 2020 21:14:42 +0100
From: Florian Lehner <dev@...-flo.net>
To: bpf@...r.kernel.org
Cc: netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
john.fastabend@...il.com, Florian Lehner <dev@...-flo.net>
Subject: [PATCH bpf-next v5] bpf: Lift hashtab key_size limit
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:
v5:
- Fix cast overflow
v4:
- Utilize BPF skeleton in tests
- Rebase
v3:
- Rebase
v2:
- Add a test for bpf side
Signed-off-by: Florian Lehner <dev@...-flo.net>
Acked-by: John Fastabend <john.fastabend@...il.com>
---
kernel/bpf/hashtab.c | 16 +++----
.../selftests/bpf/prog_tests/hash_large_key.c | 43 ++++++++++++++++++
.../selftests/bpf/progs/test_hash_large_key.c | 44 +++++++++++++++++++
tools/testing/selftests/bpf/test_maps.c | 3 +-
4 files changed, 94 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..893a60ccb2df 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 ((u64)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..34684c0fc76d
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/hash_large_key.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include "test_hash_large_key.skel.h"
+
+void test_hash_large_key(void)
+{
+ int err, value = 21, duration = 0, hash_map_fd;
+ struct test_hash_large_key *skel;
+
+ struct bigelement {
+ int a;
+ char b[4096];
+ long long c;
+ } key;
+ bzero(&key, sizeof(key));
+
+ skel = test_hash_large_key__open_and_load();
+ if (CHECK(!skel, "skel_open_and_load", "skeleton open/load failed\n"))
+ return;
+
+ hash_map_fd = bpf_map__fd(skel->maps.hash_map);
+ if (CHECK(hash_map_fd < 0, "bpf_map__fd", "failed\n"))
+ goto cleanup;
+
+ err = test_hash_large_key__attach(skel);
+ if (CHECK(err, "attach_raw_tp", "err %d\n", err))
+ goto cleanup;
+
+ err = bpf_map_update_elem(hash_map_fd, &key, &value, BPF_ANY);
+ if (CHECK(err, "bpf_map_update_elem", "errno=%d\n", errno))
+ goto cleanup;
+
+ key.c = 1;
+ err = bpf_map_lookup_elem(hash_map_fd, &key, &value);
+ if (CHECK(err, "bpf_map_lookup_elem", "errno=%d\n", errno))
+ goto cleanup;
+
+ CHECK_FAIL(value != 42);
+
+cleanup:
+ test_hash_large_key__destroy(skel);
+}
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..473a22794a62
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_hash_large_key.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+ __uint(type, BPF_MAP_TYPE_HASH);
+ __uint(max_entries, 2);
+ __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");
+
+struct bigelement {
+ int a;
+ char b[4096];
+ long long c;
+};
+
+SEC("raw_tracepoint/sys_enter")
+int bpf_hash_large_key_test(void *ctx)
+{
+ int zero = 0, err = 1, value = 42;
+ struct bigelement *key;
+
+ key = bpf_map_lookup_elem(&key_map, &zero);
+ if (!key)
+ return 0;
+
+ key->c = 1;
+ if (bpf_map_update_elem(&hash_map, key, &value, BPF_ANY))
+ return 0;
+
+ return 0;
+}
+
diff --git a/tools/testing/selftests/bpf/test_maps.c b/tools/testing/selftests/bpf/test_maps.c
index 0d92ebcb335d..0ad3e6305ff0 100644
--- a/tools/testing/selftests/bpf/test_maps.c
+++ b/tools/testing/selftests/bpf/test_maps.c
@@ -1223,9 +1223,10 @@ static void test_map_in_map(void)
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
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