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libbpf: Fix reuse of pinned map on older kernel

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[ Upstream commit 97eb31384af943d6b97eb5947262cee4ef25cb87 ]

When loading a BPF program with a pinned map, the loader checks whether
the pinned map can be reused, i.e. their properties match. To derive
such of the pinned map, the loader invokes BPF_OBJ_GET_INFO_BY_FD and
then does the comparison.

Unfortunately, on < 4.12 kernels the BPF_OBJ_GET_INFO_BY_FD is not
available, so loading the program fails with the following error:

	libbpf: failed to get map info for map FD 5: Invalid argument
	libbpf: couldn't reuse pinned map at
		'/sys/fs/bpf/tc/globals/cilium_call_policy': parameter
		mismatch"
	libbpf: map 'cilium_call_policy': error reusing pinned map
	libbpf: map 'cilium_call_policy': failed to create:
		Invalid argument(-22)
	libbpf: failed to load object 'bpf_overlay.o'

To fix this, fallback to derivation of the map properties via
/proc/$PID/fdinfo/$MAP_FD if BPF_OBJ_GET_INFO_BY_FD fails with EINVAL,
which can be used as an indicator that the kernel doesn't support
the latter.

Signed-off-by: Martynas Pumputis <m@lambda.lt>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210712125552.58705-1-m@lambda.lt
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Martynas Pumputis 2021-07-12 14:55:51 +02:00 committed by Greg Kroah-Hartman
parent 6a985c5794
commit c327b69e96
1 changed files with 45 additions and 3 deletions
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48
tools/lib/bpf/libbpf.c
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@ -3613,6 +3613,42 @@ static int bpf_map_find_btf_info(struct bpf_object *obj, struct bpf_map *map)
return 0;
}
static int bpf_get_map_info_from_fdinfo(int fd, struct bpf_map_info *info)
{
char file[PATH_MAX], buff[4096];
FILE *fp;
__u32 val;
int err;
snprintf(file, sizeof(file), "/proc/%d/fdinfo/%d", getpid(), fd);
memset(info, 0, sizeof(*info));
fp = fopen(file, "r");
if (!fp) {
err = -errno;
pr_warn("failed to open %s: %d. No procfs support?\n", file,
err);
return err;
}
while (fgets(buff, sizeof(buff), fp)) {
if (sscanf(buff, "map_type:\t%u", &val) == 1)
info->type = val;
else if (sscanf(buff, "key_size:\t%u", &val) == 1)
info->key_size = val;
else if (sscanf(buff, "value_size:\t%u", &val) == 1)
info->value_size = val;
else if (sscanf(buff, "max_entries:\t%u", &val) == 1)
info->max_entries = val;
else if (sscanf(buff, "map_flags:\t%i", &val) == 1)
info->map_flags = val;
}
fclose(fp);
return 0;
}
int bpf_map__reuse_fd(struct bpf_map *map, int fd)
{
struct bpf_map_info info = {};
@ -3621,6 +3657,8 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
char *new_name;
err = bpf_obj_get_info_by_fd(fd, &info, &len);
if (err && errno == EINVAL)
err = bpf_get_map_info_from_fdinfo(fd, &info);
if (err)
return err;
@ -4032,12 +4070,16 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
struct bpf_map_info map_info = {};
char msg[STRERR_BUFSIZE];
__u32 map_info_len;
int err;
map_info_len = sizeof(map_info);
if (bpf_obj_get_info_by_fd(map_fd, &map_info, &map_info_len)) {
pr_warn("failed to get map info for map FD %d: %s\n",
map_fd, libbpf_strerror_r(errno, msg, sizeof(msg)));
err = bpf_obj_get_info_by_fd(map_fd, &map_info, &map_info_len);
if (err && errno == EINVAL)
err = bpf_get_map_info_from_fdinfo(map_fd, &map_info);
if (err) {
pr_warn("failed to get map info for map FD %d: %s\n", map_fd,
libbpf_strerror_r(errno, msg, sizeof(msg)));
return false;
}