[PATCH RESEND bpf-next 07/18] bpf: add BPF token support to BPF_MAP_CREATE command
Andrii Nakryiko
andrii at kernel.org
Fri Jun 2 15:00:00 UTC 2023
Allow providing token_fd for BPF_MAP_CREATE command to allow controlled
BPF map creation from unprivileged process through delegated BPF token.
Further, add a filter of allowed BPF map types to BPF token, specified
at BPF token creation time. This, in combination with allowed_cmds
allows to create a narrowly-focused BPF token (controlled by privileged
agent) with a restrictive set of BPF maps that application can attempt
to create.
BPF_F_TOKEN_IGNORE_UNKNOWN_MAP_TYPES flag allows application to express
"any supported BPF map type" without having to do an elaborate feature
detection of each supported BPF map. This is a very untrivial process,
especially as some BPF maps have special requirements just to be able to
instantiate a minimal instance (e.g., custom BTF). Allowing application
to just specify ~0 as a bit set makes writing application much simple
without degrading any of kernel's safety of backwards compatibility
concerns.
Signed-off-by: Andrii Nakryiko <andrii at kernel.org>
---
include/linux/bpf.h | 3 +
include/uapi/linux/bpf.h | 12 +++
kernel/bpf/syscall.c | 82 +++++++++++++++----
kernel/bpf/token.c | 8 ++
tools/include/uapi/linux/bpf.h | 16 +++-
.../selftests/bpf/prog_tests/libbpf_str.c | 3 +
6 files changed, 108 insertions(+), 16 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index fe6d51c3a5b1..657bec546351 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -251,6 +251,7 @@ struct bpf_map {
u32 btf_value_type_id;
u32 btf_vmlinux_value_type_id;
struct btf *btf;
+ struct bpf_token *token;
#ifdef CONFIG_MEMCG_KMEM
struct obj_cgroup *objcg;
#endif
@@ -1538,6 +1539,7 @@ struct bpf_token {
struct work_struct work;
atomic64_t refcnt;
u64 allowed_cmds;
+ u64 allowed_map_types;
};
struct bpf_struct_ops_value;
@@ -2092,6 +2094,7 @@ struct bpf_token *bpf_token_get_from_fd(u32 ufd);
bool bpf_token_capable(const struct bpf_token *token, int cap);
bool bpf_token_allow_cmd(const struct bpf_token *token, enum bpf_cmd cmd);
+bool bpf_token_allow_map_type(const struct bpf_token *token, enum bpf_map_type type);
int bpf_obj_pin_user(u32 ufd, int path_fd, const char __user *pathname);
int bpf_obj_get_user(int path_fd, const char __user *pathname, int flags);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 01ab79f2ad9f..7cfaa2da84ee 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -954,6 +954,7 @@ enum bpf_map_type {
BPF_MAP_TYPE_BLOOM_FILTER,
BPF_MAP_TYPE_USER_RINGBUF,
BPF_MAP_TYPE_CGRP_STORAGE,
+ __MAX_BPF_MAP_TYPE
};
/* Note that tracing related programs such as
@@ -1196,6 +1197,10 @@ enum {
* token-enabled.
*/
BPF_F_TOKEN_IGNORE_UNKNOWN_CMDS = 1U << 0,
+ /* Similar to BPF_F_TOKEN_IGNORE_UNKNOWN_CMDS flag, but for
+ * token_create.allowed_map_types bit set.
+ */
+ BPF_F_TOKEN_IGNORE_UNKNOWN_MAP_TYPES = 1U << 1,
};
/* When BPF ldimm64's insn[0].src_reg != 0 then this can have
@@ -1377,6 +1382,7 @@ union bpf_attr {
* to using 5 hash functions).
*/
__u64 map_extra;
+ __u32 map_token_fd;
};
struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */
@@ -1661,6 +1667,12 @@ union bpf_attr {
* validity checking of this set
*/
__u64 allowed_cmds;
+ /* similarly to allowed_cmds, a bit set of BPF map types that
+ * are allowed to be created by requested BPF token;
+ * see also BPF_F_TOKEN_IGNORE_UNKNOWN_MAP_TYPES for its
+ * effect on validity checking of this set
+ */
+ __u64 allowed_map_types;
} token_create;
} __attribute__((aligned(8)));
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6e7ccbd54524..eb77ba71fbcf 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -691,6 +691,7 @@ static void bpf_map_free_deferred(struct work_struct *work)
{
struct bpf_map *map = container_of(work, struct bpf_map, work);
struct btf_record *rec = map->record;
+ struct bpf_token *token = map->token;
security_bpf_map_free(map);
bpf_map_release_memcg(map);
@@ -706,6 +707,7 @@ static void bpf_map_free_deferred(struct work_struct *work)
* template bpf_map struct used during verification.
*/
btf_record_free(rec);
+ bpf_token_put(token);
}
static void bpf_map_put_uref(struct bpf_map *map)
@@ -1010,7 +1012,7 @@ static int map_check_btf(struct bpf_map *map, const struct btf *btf,
if (!IS_ERR_OR_NULL(map->record)) {
int i;
- if (!bpf_capable()) {
+ if (!bpf_token_capable(map->token, CAP_BPF)) {
ret = -EPERM;
goto free_map_tab;
}
@@ -1092,11 +1094,12 @@ static int map_check_btf(struct bpf_map *map, const struct btf *btf,
return ret;
}
-#define BPF_MAP_CREATE_LAST_FIELD map_extra
+#define BPF_MAP_CREATE_LAST_FIELD map_token_fd
/* called via syscall */
static int map_create(union bpf_attr *attr)
{
const struct bpf_map_ops *ops;
+ struct bpf_token *token = NULL;
int numa_node = bpf_map_attr_numa_node(attr);
u32 map_type = attr->map_type;
struct bpf_map *map;
@@ -1147,14 +1150,32 @@ static int map_create(union bpf_attr *attr)
if (!ops->map_mem_usage)
return -EINVAL;
+ if (attr->map_token_fd) {
+ token = bpf_token_get_from_fd(attr->map_token_fd);
+ if (IS_ERR(token))
+ return PTR_ERR(token);
+
+ /* if current token doesn't grant map creation permissions,
+ * then we can't use this token, so ignore it and rely on
+ * system-wide capabilities checks
+ */
+ if (!bpf_token_allow_cmd(token, BPF_MAP_CREATE) ||
+ !bpf_token_allow_map_type(token, attr->map_type)) {
+ bpf_token_put(token);
+ token = NULL;
+ }
+ }
+
+ err = -EPERM;
+
/* Intent here is for unprivileged_bpf_disabled to block BPF map
* creation for unprivileged users; other actions depend
* on fd availability and access to bpffs, so are dependent on
* object creation success. Even with unprivileged BPF disabled,
* capability checks are still carried out.
*/
- if (sysctl_unprivileged_bpf_disabled && !bpf_capable())
- return -EPERM;
+ if (sysctl_unprivileged_bpf_disabled && !bpf_token_capable(token, CAP_BPF))
+ goto put_token;
/* check privileged map type permissions */
switch (map_type) {
@@ -1187,28 +1208,36 @@ static int map_create(union bpf_attr *attr)
case BPF_MAP_TYPE_LRU_PERCPU_HASH:
case BPF_MAP_TYPE_STRUCT_OPS:
case BPF_MAP_TYPE_CPUMAP:
- if (!bpf_capable())
- return -EPERM;
+ if (!bpf_token_capable(token, CAP_BPF))
+ goto put_token;
break;
case BPF_MAP_TYPE_SOCKMAP:
case BPF_MAP_TYPE_SOCKHASH:
case BPF_MAP_TYPE_DEVMAP:
case BPF_MAP_TYPE_DEVMAP_HASH:
case BPF_MAP_TYPE_XSKMAP:
- if (!capable(CAP_NET_ADMIN))
- return -EPERM;
+ if (!bpf_token_capable(token, CAP_NET_ADMIN))
+ goto put_token;
break;
default:
WARN(1, "unsupported map type %d", map_type);
- return -EPERM;
+ goto put_token;
}
map = ops->map_alloc(attr);
- if (IS_ERR(map))
- return PTR_ERR(map);
+ if (IS_ERR(map)) {
+ err = PTR_ERR(map);
+ goto put_token;
+ }
map->ops = ops;
map->map_type = map_type;
+ if (token) {
+ /* move token reference into map->token, reuse our refcnt */
+ map->token = token;
+ token = NULL;
+ }
+
err = bpf_obj_name_cpy(map->name, attr->map_name,
sizeof(attr->map_name));
if (err < 0)
@@ -1281,8 +1310,11 @@ static int map_create(union bpf_attr *attr)
free_map_sec:
security_bpf_map_free(map);
free_map:
+ bpf_token_put(map->token);
btf_put(map->btf);
map->ops->map_free(map);
+put_token:
+ bpf_token_put(token);
return err;
}
@@ -5081,15 +5113,23 @@ static int bpf_prog_bind_map(union bpf_attr *attr)
return ret;
}
-#define BPF_TOKEN_FLAGS_MASK (BPF_F_TOKEN_IGNORE_UNKNOWN_CMDS)
-#define BPF_TOKEN_CMDS_MASK ((1ULL << BPF_TOKEN_CREATE))
+#define BPF_TOKEN_FLAGS_MASK ( \
+ BPF_F_TOKEN_IGNORE_UNKNOWN_CMDS \
+ | BPF_F_TOKEN_IGNORE_UNKNOWN_MAP_TYPES \
+)
+#define BPF_TOKEN_CMDS_MASK ( \
+ (1ULL << BPF_TOKEN_CREATE) \
+ | (1ULL << BPF_MAP_CREATE) \
+)
+#define BPF_TOKEN_MAP_TYPES_MASK \
+ ((BIT_ULL(__MAX_BPF_MAP_TYPE) - 1) & ~BIT_ULL(BPF_MAP_TYPE_UNSPEC))
-#define BPF_TOKEN_CREATE_LAST_FIELD token_create.allowed_cmds
+#define BPF_TOKEN_CREATE_LAST_FIELD token_create.allowed_map_types
static int token_create(union bpf_attr *attr)
{
struct bpf_token *new_token, *token = NULL;
- u64 allowed_cmds;
+ u64 allowed_cmds, allowed_map_types;
int fd, err;
if (CHECK_ATTR(BPF_TOKEN_CREATE))
@@ -5117,6 +5157,12 @@ static int token_create(union bpf_attr *attr)
err = -ENOTSUPP;
goto err_out;
}
+ allowed_map_types = attr->token_create.allowed_map_types;
+ if (!(attr->token_create.flags & BPF_F_TOKEN_IGNORE_UNKNOWN_MAP_TYPES) &&
+ allowed_map_types & ~BPF_TOKEN_MAP_TYPES_MASK) {
+ err = -ENOTSUPP;
+ goto err_out;
+ }
if (!bpf_token_capable(token, CAP_SYS_ADMIN)) {
err = -EPERM;
@@ -5128,6 +5174,11 @@ static int token_create(union bpf_attr *attr)
err = -EPERM;
goto err_out;
}
+ /* requested map types should be a subset of associated token's set */
+ if (token && (token->allowed_map_types & allowed_map_types) != allowed_map_types) {
+ err = -EPERM;
+ goto err_out;
+ }
new_token = bpf_token_alloc();
if (!new_token) {
@@ -5136,6 +5187,7 @@ static int token_create(union bpf_attr *attr)
}
new_token->allowed_cmds = allowed_cmds & BPF_TOKEN_CMDS_MASK;
+ new_token->allowed_map_types = allowed_map_types & BPF_TOKEN_MAP_TYPES_MASK;
fd = bpf_token_new_fd(new_token);
if (fd < 0) {
diff --git a/kernel/bpf/token.c b/kernel/bpf/token.c
index 7e989b25fa06..ef053c48d7db 100644
--- a/kernel/bpf/token.c
+++ b/kernel/bpf/token.c
@@ -116,6 +116,14 @@ bool bpf_token_allow_cmd(const struct bpf_token *token, enum bpf_cmd cmd)
return token->allowed_cmds & (1ULL << cmd);
}
+bool bpf_token_allow_map_type(const struct bpf_token *token, enum bpf_map_type type)
+{
+ if (!token || type >= __MAX_BPF_MAP_TYPE)
+ return false;
+
+ return token->allowed_map_types & (1ULL << type);
+}
+
bool bpf_token_capable(const struct bpf_token *token, int cap)
{
return token || capable(cap) || (cap != CAP_SYS_ADMIN && capable(CAP_SYS_ADMIN));
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index d1d7ca71756f..7cfaa2da84ee 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -954,6 +954,7 @@ enum bpf_map_type {
BPF_MAP_TYPE_BLOOM_FILTER,
BPF_MAP_TYPE_USER_RINGBUF,
BPF_MAP_TYPE_CGRP_STORAGE,
+ __MAX_BPF_MAP_TYPE
};
/* Note that tracing related programs such as
@@ -1196,6 +1197,10 @@ enum {
* token-enabled.
*/
BPF_F_TOKEN_IGNORE_UNKNOWN_CMDS = 1U << 0,
+ /* Similar to BPF_F_TOKEN_IGNORE_UNKNOWN_CMDS flag, but for
+ * token_create.allowed_map_types bit set.
+ */
+ BPF_F_TOKEN_IGNORE_UNKNOWN_MAP_TYPES = 1U << 1,
};
/* When BPF ldimm64's insn[0].src_reg != 0 then this can have
@@ -1377,6 +1382,7 @@ union bpf_attr {
* to using 5 hash functions).
*/
__u64 map_extra;
+ __u32 map_token_fd;
};
struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */
@@ -1656,9 +1662,17 @@ union bpf_attr {
/* a bit set of allowed bpf() syscall commands,
* e.g., (1ULL << BPF_TOKEN_CREATE) | (1ULL << BPF_PROG_LOAD)
* will allow creating derived BPF tokens and loading new BPF
- * programs
+ * programs;
+ * see also BPF_F_TOKEN_IGNORE_UNKNOWN_CMDS for its effect on
+ * validity checking of this set
*/
__u64 allowed_cmds;
+ /* similarly to allowed_cmds, a bit set of BPF map types that
+ * are allowed to be created by requested BPF token;
+ * see also BPF_F_TOKEN_IGNORE_UNKNOWN_MAP_TYPES for its
+ * effect on validity checking of this set
+ */
+ __u64 allowed_map_types;
} token_create;
} __attribute__((aligned(8)));
diff --git a/tools/testing/selftests/bpf/prog_tests/libbpf_str.c b/tools/testing/selftests/bpf/prog_tests/libbpf_str.c
index efb8bd43653c..e677c0435cec 100644
--- a/tools/testing/selftests/bpf/prog_tests/libbpf_str.c
+++ b/tools/testing/selftests/bpf/prog_tests/libbpf_str.c
@@ -132,6 +132,9 @@ static void test_libbpf_bpf_map_type_str(void)
const char *map_type_str;
char buf[256];
+ if (map_type == __MAX_BPF_MAP_TYPE)
+ continue;
+
map_type_name = btf__str_by_offset(btf, e->name_off);
map_type_str = libbpf_bpf_map_type_str(map_type);
ASSERT_OK_PTR(map_type_str, map_type_name);
--
2.34.1
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