Commit c6bde958 authored by Florian Lehner's avatar Florian Lehner Committed by Alexei Starovoitov

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: default avatarFlorian Lehner <dev@der-flo.net>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20201029201442.596690-1-dev@der-flo.net
parent b6b466a8
...@@ -415,17 +415,11 @@ static int htab_map_alloc_check(union bpf_attr *attr) ...@@ -415,17 +415,11 @@ static int htab_map_alloc_check(union bpf_attr *attr)
attr->value_size == 0) attr->value_size == 0)
return -EINVAL; return -EINVAL;
if (attr->key_size > MAX_BPF_STACK) if ((u64)attr->key_size + attr->value_size >= KMALLOC_MAX_SIZE -
/* eBPF programs initialize keys on stack, so they cannot be sizeof(struct htab_elem))
* larger than max stack size /* if key_size + value_size is bigger, the user space won't be
*/ * able to access the elements via bpf syscall. This check
return -E2BIG; * also makes sure that the elem_size doesn't overflow and it's
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
* kmalloc-able later in htab_map_update_elem() * kmalloc-able later in htab_map_update_elem()
*/ */
return -E2BIG; return -E2BIG;
......
// 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);
}
// 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;
}
...@@ -1223,9 +1223,10 @@ static void test_map_in_map(void) ...@@ -1223,9 +1223,10 @@ static void test_map_in_map(void)
static void test_map_large(void) static void test_map_large(void)
{ {
struct bigkey { struct bigkey {
int a; int a;
char b[116]; char b[4096];
long long c; long long c;
} key; } key;
int fd, i, value; int fd, i, value;
......
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