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Merge branch 'Fix for crash due to overwrite in copy_map_value'

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Kumar Kartikeya says:

====================

A fix for an oversight in copy_map_value that leads to kernel crash.

Also, a question for BPF developers:
It seems in arraymap.c, we always do check_and_free_timer_in_array after we do
copy_map_value in map_update_elem callback, but the same is not done for
hashtab.c. Is there a specific reason for this difference in behavior, or did I
miss that it happens for hashtab.c as well?

Changlog:
---------
v1 -> v2:
v1: https://lore.kernel.org/bpf/20220209051113.870717-1-memxor@gmail.com

 * Fix build error for selftests patch due to missing SYS_PREFIX in bpf tree
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov 2022-02-11 13:13:04 -08:00
commit acc3c47394
3 changed files with 88 additions and 1 deletions
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3
include/linux/bpf.h
View File

@ -224,7 +224,8 @@ static inline void copy_map_value(struct bpf_map *map, void *dst, void *src)
if (unlikely(map_value_has_spin_lock(map))) {
s_off = map->spin_lock_off;
s_sz = sizeof(struct bpf_spin_lock);
} else if (unlikely(map_value_has_timer(map))) {
}
if (unlikely(map_value_has_timer(map))) {
t_off = map->timer_off;
t_sz = sizeof(struct bpf_timer);
}

32
tools/testing/selftests/bpf/prog_tests/timer_crash.c Normal file
View File

@ -0,0 +1,32 @@
// SPDX-License-Identifier: GPL-2.0
#include <test_progs.h>
#include "timer_crash.skel.h"
enum {
MODE_ARRAY,
MODE_HASH,
};
static void test_timer_crash_mode(int mode)
{
struct timer_crash *skel;
skel = timer_crash__open_and_load();
if (!ASSERT_OK_PTR(skel, "timer_crash__open_and_load"))
return;
skel->bss->pid = getpid();
skel->bss->crash_map = mode;
if (!ASSERT_OK(timer_crash__attach(skel), "timer_crash__attach"))
goto end;
usleep(1);
end:
timer_crash__destroy(skel);
}
void test_timer_crash(void)
{
if (test__start_subtest("array"))
test_timer_crash_mode(MODE_ARRAY);
if (test__start_subtest("hash"))
test_timer_crash_mode(MODE_HASH);
}

54
tools/testing/selftests/bpf/progs/timer_crash.c Normal file
View File

@ -0,0 +1,54 @@
// SPDX-License-Identifier: GPL-2.0
#include <vmlinux.h>
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_helpers.h>
struct map_elem {
struct bpf_timer timer;
struct bpf_spin_lock lock;
};
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__uint(max_entries, 1);
__type(key, int);
__type(value, struct map_elem);
} amap SEC(".maps");
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(max_entries, 1);
__type(key, int);
__type(value, struct map_elem);
} hmap SEC(".maps");
int pid = 0;
int crash_map = 0; /* 0 for amap, 1 for hmap */
SEC("fentry/do_nanosleep")
int sys_enter(void *ctx)
{
struct map_elem *e, value = {};
void *map = crash_map ? (void *)&hmap : (void *)&amap;
if (bpf_get_current_task_btf()->tgid != pid)
return 0;
*(void **)&value = (void *)0xdeadcaf3;
bpf_map_update_elem(map, &(int){0}, &value, 0);
/* For array map, doing bpf_map_update_elem will do a
* check_and_free_timer_in_array, which will trigger the crash if timer
* pointer was overwritten, for hmap we need to use bpf_timer_cancel.
*/
if (crash_map == 1) {
e = bpf_map_lookup_elem(map, &(int){0});
if (!e)
return 0;
bpf_timer_cancel(&e->timer);
}
return 0;
}
char _license[] SEC("license") = "GPL";