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selftests/bpf: Add test for prealloc_lru_pop bug

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Add a regression test to check against invalid check_and_init_map_value
call inside prealloc_lru_pop.

The kptr should not be reset to NULL once we set it after deleting the
map element. Hence, we trigger a program that updates the element
causing its reuse, and checks whether the unref kptr is reset or not.
If it is, prealloc_lru_pop does an incorrect check_and_init_map_value
call and the test fails.

Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220809213033.24147-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi 2022-08-09 23:30:33 +02:00 committed by Alexei Starovoitov
parent 275c30bcee
commit de7b992710
2 changed files with 70 additions and 0 deletions
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21
tools/testing/selftests/bpf/prog_tests/lru_bug.c Normal file
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// SPDX-License-Identifier: GPL-2.0
#include <test_progs.h>
#include "lru_bug.skel.h"
void test_lru_bug(void)
{
struct lru_bug *skel;
int ret;
skel = lru_bug__open_and_load();
if (!ASSERT_OK_PTR(skel, "lru_bug__open_and_load"))
return;
ret = lru_bug__attach(skel);
if (!ASSERT_OK(ret, "lru_bug__attach"))
goto end;
usleep(1);
ASSERT_OK(skel->data->result, "prealloc_lru_pop doesn't call check_and_init_map_value");
end:
lru_bug__destroy(skel);
}

49
tools/testing/selftests/bpf/progs/lru_bug.c Normal file
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// SPDX-License-Identifier: GPL-2.0
#include <vmlinux.h>
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_helpers.h>
struct map_value {
struct task_struct __kptr *ptr;
};
struct {
__uint(type, BPF_MAP_TYPE_LRU_HASH);
__uint(max_entries, 1);
__type(key, int);
__type(value, struct map_value);
} lru_map SEC(".maps");
int pid = 0;
int result = 1;
SEC("fentry/bpf_ktime_get_ns")
int printk(void *ctx)
{
struct map_value v = {};
if (pid == bpf_get_current_task_btf()->pid)
bpf_map_update_elem(&lru_map, &(int){0}, &v, 0);
return 0;
}
SEC("fentry/do_nanosleep")
int nanosleep(void *ctx)
{
struct map_value val = {}, *v;
struct task_struct *current;
bpf_map_update_elem(&lru_map, &(int){0}, &val, 0);
v = bpf_map_lookup_elem(&lru_map, &(int){0});
if (!v)
return 0;
bpf_map_delete_elem(&lru_map, &(int){0});
current = bpf_get_current_task_btf();
v->ptr = current;
pid = current->pid;
bpf_ktime_get_ns();
result = !v->ptr;
return 0;
}
char _license[] SEC("license") = "GPL";