struct cgroup is already an RCU-safe type in the verifier. We can
therefore update bpf_cgroup_acquire() to be KF_RCU | KF_RET_NULL, and
subsequently remove bpf_cgroup_kptr_get(). This patch does the first of
these by updating bpf_cgroup_acquire() to be KF_RCU | KF_RET_NULL, and
also updates selftests accordingly.
Signed-off-by: David Vernet <[email protected]>
---
kernel/bpf/helpers.c | 5 ++-
.../selftests/bpf/progs/cgrp_kfunc_common.h | 5 +++
.../selftests/bpf/progs/cgrp_kfunc_failure.c | 35 +++++++++++++++----
.../selftests/bpf/progs/cgrp_kfunc_success.c | 5 ++-
4 files changed, 40 insertions(+), 10 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b6a5cda5bb59..71f0604bdc97 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2037,8 +2037,7 @@ __bpf_kfunc void bpf_task_release(struct task_struct *p)
*/
__bpf_kfunc struct cgroup *bpf_cgroup_acquire(struct cgroup *cgrp)
{
- cgroup_get(cgrp);
- return cgrp;
+ return cgroup_tryget(cgrp) ? cgrp : NULL;
}
/**
@@ -2314,7 +2313,7 @@ BTF_ID_FLAGS(func, bpf_rbtree_add)
BTF_ID_FLAGS(func, bpf_rbtree_first, KF_RET_NULL)
#ifdef CONFIG_CGROUPS
-BTF_ID_FLAGS(func, bpf_cgroup_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_cgroup_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_cgroup_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_cgroup_release, KF_RELEASE)
BTF_ID_FLAGS(func, bpf_cgroup_ancestor, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
index d0b7cd0d09d7..b0e279f4652b 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
@@ -61,6 +61,11 @@ static inline int cgrps_kfunc_map_insert(struct cgroup *cgrp)
}
acquired = bpf_cgroup_acquire(cgrp);
+ if (!acquired) {
+ bpf_map_delete_elem(&__cgrps_kfunc_map, &id);
+ return -ENOENT;
+ }
+
old = bpf_kptr_xchg(&v->cgrp, acquired);
if (old) {
bpf_cgroup_release(old);
diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c b/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
index 48b2034cadb3..49347f12de39 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
@@ -41,6 +41,23 @@ int BPF_PROG(cgrp_kfunc_acquire_untrusted, struct cgroup *cgrp, const char *path
/* Can't invoke bpf_cgroup_acquire() on an untrusted pointer. */
acquired = bpf_cgroup_acquire(v->cgrp);
+ if (acquired)
+ bpf_cgroup_release(acquired);
+
+ return 0;
+}
+
+SEC("tp_btf/cgroup_mkdir")
+__failure __msg("Possibly NULL pointer passed to trusted arg0")
+int BPF_PROG(cgrp_kfunc_acquire_no_null_check, struct cgroup *cgrp, const char *path)
+{
+ struct cgroup *acquired;
+
+ acquired = bpf_cgroup_acquire(cgrp);
+ /*
+ * Can't invoke bpf_cgroup_release() without checking the return value
+ * of bpf_cgroup_acquire().
+ */
bpf_cgroup_release(acquired);
return 0;
@@ -54,7 +71,8 @@ int BPF_PROG(cgrp_kfunc_acquire_fp, struct cgroup *cgrp, const char *path)
/* Can't invoke bpf_cgroup_acquire() on a random frame pointer. */
acquired = bpf_cgroup_acquire((struct cgroup *)&stack_cgrp);
- bpf_cgroup_release(acquired);
+ if (acquired)
+ bpf_cgroup_release(acquired);
return 0;
}
@@ -67,7 +85,8 @@ int BPF_PROG(cgrp_kfunc_acquire_unsafe_kretprobe, struct cgroup *cgrp)
/* Can't acquire an untrusted struct cgroup * pointer. */
acquired = bpf_cgroup_acquire(cgrp);
- bpf_cgroup_release(acquired);
+ if (acquired)
+ bpf_cgroup_release(acquired);
return 0;
}
@@ -80,7 +99,8 @@ int BPF_PROG(cgrp_kfunc_acquire_trusted_walked, struct cgroup *cgrp, const char
/* Can't invoke bpf_cgroup_acquire() on a pointer obtained from walking a trusted cgroup. */
acquired = bpf_cgroup_acquire(cgrp->old_dom_cgrp);
- bpf_cgroup_release(acquired);
+ if (acquired)
+ bpf_cgroup_release(acquired);
return 0;
}
@@ -93,9 +113,8 @@ int BPF_PROG(cgrp_kfunc_acquire_null, struct cgroup *cgrp, const char *path)
/* Can't invoke bpf_cgroup_acquire() on a NULL pointer. */
acquired = bpf_cgroup_acquire(NULL);
- if (!acquired)
- return 0;
- bpf_cgroup_release(acquired);
+ if (acquired)
+ bpf_cgroup_release(acquired);
return 0;
}
@@ -137,6 +156,8 @@ int BPF_PROG(cgrp_kfunc_get_non_kptr_acquired, struct cgroup *cgrp, const char *
struct cgroup *kptr, *acquired;
acquired = bpf_cgroup_acquire(cgrp);
+ if (!acquired)
+ return 0;
/* Cannot use bpf_cgroup_kptr_get() on a non-map-value, even if the kptr was acquired. */
kptr = bpf_cgroup_kptr_get(&acquired);
@@ -256,6 +277,8 @@ int BPF_PROG(cgrp_kfunc_release_null, struct cgroup *cgrp, const char *path)
return -ENOENT;
acquired = bpf_cgroup_acquire(cgrp);
+ if (!acquired)
+ return -ENOENT;
old = bpf_kptr_xchg(&v->cgrp, acquired);
diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c b/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
index 030aff700084..e9dbd1af05a7 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
@@ -38,7 +38,10 @@ int BPF_PROG(test_cgrp_acquire_release_argument, struct cgroup *cgrp, const char
return 0;
acquired = bpf_cgroup_acquire(cgrp);
- bpf_cgroup_release(acquired);
+ if (!acquired)
+ err = 1;
+ else
+ bpf_cgroup_release(acquired);
return 0;
}
--
2.40.0
Now that bpf_cgroup_acquire() is KF_RCU | KF_RET_NULL,
bpf_cgroup_kptr_get() is redundant. Let's remove it, and update
selftests to instead use bpf_cgroup_acquire() where appropriate. The
next patch will update the BPF documentation to not mention
bpf_cgroup_kptr_get().
Signed-off-by: David Vernet <[email protected]>
---
kernel/bpf/helpers.c | 32 ---------
.../selftests/bpf/progs/cgrp_kfunc_common.h | 3 +-
.../selftests/bpf/progs/cgrp_kfunc_failure.c | 68 +++----------------
.../selftests/bpf/progs/cgrp_kfunc_success.c | 10 ++-
4 files changed, 14 insertions(+), 99 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 71f0604bdc97..f04e60a4847f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2040,37 +2040,6 @@ __bpf_kfunc struct cgroup *bpf_cgroup_acquire(struct cgroup *cgrp)
return cgroup_tryget(cgrp) ? cgrp : NULL;
}
-/**
- * bpf_cgroup_kptr_get - Acquire a reference on a struct cgroup kptr. A cgroup
- * kptr acquired by this kfunc which is not subsequently stored in a map, must
- * be released by calling bpf_cgroup_release().
- * @cgrpp: A pointer to a cgroup kptr on which a reference is being acquired.
- */
-__bpf_kfunc struct cgroup *bpf_cgroup_kptr_get(struct cgroup **cgrpp)
-{
- struct cgroup *cgrp;
-
- rcu_read_lock();
- /* Another context could remove the cgroup from the map and release it
- * at any time, including after we've done the lookup above. This is
- * safe because we're in an RCU read region, so the cgroup is
- * guaranteed to remain valid until at least the rcu_read_unlock()
- * below.
- */
- cgrp = READ_ONCE(*cgrpp);
-
- if (cgrp && !cgroup_tryget(cgrp))
- /* If the cgroup had been removed from the map and freed as
- * described above, cgroup_tryget() will return false. The
- * cgroup will be freed at some point after the current RCU gp
- * has ended, so just return NULL to the user.
- */
- cgrp = NULL;
- rcu_read_unlock();
-
- return cgrp;
-}
-
/**
* bpf_cgroup_release - Release the reference acquired on a cgroup.
* If this kfunc is invoked in an RCU read region, the cgroup is guaranteed to
@@ -2314,7 +2283,6 @@ BTF_ID_FLAGS(func, bpf_rbtree_first, KF_RET_NULL)
#ifdef CONFIG_CGROUPS
BTF_ID_FLAGS(func, bpf_cgroup_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
-BTF_ID_FLAGS(func, bpf_cgroup_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_cgroup_release, KF_RELEASE)
BTF_ID_FLAGS(func, bpf_cgroup_ancestor, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_cgroup_from_id, KF_ACQUIRE | KF_RET_NULL)
diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
index b0e279f4652b..22914a70db54 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
@@ -21,10 +21,11 @@ struct hash_map {
} __cgrps_kfunc_map SEC(".maps");
struct cgroup *bpf_cgroup_acquire(struct cgroup *p) __ksym;
-struct cgroup *bpf_cgroup_kptr_get(struct cgroup **pp) __ksym;
void bpf_cgroup_release(struct cgroup *p) __ksym;
struct cgroup *bpf_cgroup_ancestor(struct cgroup *cgrp, int level) __ksym;
struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
+void bpf_rcu_read_lock(void) __ksym;
+void bpf_rcu_read_unlock(void) __ksym;
static inline struct __cgrps_kfunc_map_value *cgrps_kfunc_map_value_lookup(struct cgroup *cgrp)
{
diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c b/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
index 49347f12de39..0fa564a5cc5b 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
@@ -133,59 +133,6 @@ int BPF_PROG(cgrp_kfunc_acquire_unreleased, struct cgroup *cgrp, const char *pat
return 0;
}
-SEC("tp_btf/cgroup_mkdir")
-__failure __msg("arg#0 expected pointer to map value")
-int BPF_PROG(cgrp_kfunc_get_non_kptr_param, struct cgroup *cgrp, const char *path)
-{
- struct cgroup *kptr;
-
- /* Cannot use bpf_cgroup_kptr_get() on a non-kptr, even on a valid cgroup. */
- kptr = bpf_cgroup_kptr_get(&cgrp);
- if (!kptr)
- return 0;
-
- bpf_cgroup_release(kptr);
-
- return 0;
-}
-
-SEC("tp_btf/cgroup_mkdir")
-__failure __msg("arg#0 expected pointer to map value")
-int BPF_PROG(cgrp_kfunc_get_non_kptr_acquired, struct cgroup *cgrp, const char *path)
-{
- struct cgroup *kptr, *acquired;
-
- acquired = bpf_cgroup_acquire(cgrp);
- if (!acquired)
- return 0;
-
- /* Cannot use bpf_cgroup_kptr_get() on a non-map-value, even if the kptr was acquired. */
- kptr = bpf_cgroup_kptr_get(&acquired);
- bpf_cgroup_release(acquired);
- if (!kptr)
- return 0;
-
- bpf_cgroup_release(kptr);
-
- return 0;
-}
-
-SEC("tp_btf/cgroup_mkdir")
-__failure __msg("arg#0 expected pointer to map value")
-int BPF_PROG(cgrp_kfunc_get_null, struct cgroup *cgrp, const char *path)
-{
- struct cgroup *kptr;
-
- /* Cannot use bpf_cgroup_kptr_get() on a NULL pointer. */
- kptr = bpf_cgroup_kptr_get(NULL);
- if (!kptr)
- return 0;
-
- bpf_cgroup_release(kptr);
-
- return 0;
-}
-
SEC("tp_btf/cgroup_mkdir")
__failure __msg("Unreleased reference")
int BPF_PROG(cgrp_kfunc_xchg_unreleased, struct cgroup *cgrp, const char *path)
@@ -207,8 +154,8 @@ int BPF_PROG(cgrp_kfunc_xchg_unreleased, struct cgroup *cgrp, const char *path)
}
SEC("tp_btf/cgroup_mkdir")
-__failure __msg("Unreleased reference")
-int BPF_PROG(cgrp_kfunc_get_unreleased, struct cgroup *cgrp, const char *path)
+__failure __msg("must be referenced or trusted")
+int BPF_PROG(cgrp_kfunc_rcu_get_release, struct cgroup *cgrp, const char *path)
{
struct cgroup *kptr;
struct __cgrps_kfunc_map_value *v;
@@ -217,11 +164,12 @@ int BPF_PROG(cgrp_kfunc_get_unreleased, struct cgroup *cgrp, const char *path)
if (!v)
return 0;
- kptr = bpf_cgroup_kptr_get(&v->cgrp);
- if (!kptr)
- return 0;
-
- /* Kptr acquired above is never released. */
+ bpf_rcu_read_lock();
+ kptr = v->cgrp;
+ if (kptr)
+ /* Can't release a cgroup kptr stored in a map. */
+ bpf_cgroup_release(kptr);
+ bpf_rcu_read_unlock();
return 0;
}
diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c b/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
index e9dbd1af05a7..5354455a01be 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
+++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
@@ -126,13 +126,11 @@ int BPF_PROG(test_cgrp_get_release, struct cgroup *cgrp, const char *path)
return 0;
}
- kptr = bpf_cgroup_kptr_get(&v->cgrp);
- if (!kptr) {
+ bpf_rcu_read_lock();
+ kptr = v->cgrp;
+ if (!kptr)
err = 3;
- return 0;
- }
-
- bpf_cgroup_release(kptr);
+ bpf_rcu_read_unlock();
return 0;
}
--
2.40.0
The bpf_cgroup_kptr_get() kfunc has been removed, and
bpf_cgroup_acquire() / bpf_cgroup_release() now have the same semantics
as bpf_task_acquire() / bpf_task_release(). This patch updates the BPF
documentation to reflect this.
Signed-off-by: David Vernet <[email protected]>
---
Documentation/bpf/kfuncs.rst | 68 ------------------------------------
1 file changed, 68 deletions(-)
diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
index d8a16c4bef7f..3b42cfe12437 100644
--- a/Documentation/bpf/kfuncs.rst
+++ b/Documentation/bpf/kfuncs.rst
@@ -572,74 +572,6 @@ bpf_task_release() respectively, so we won't provide examples for them.
----
-You may also acquire a reference to a ``struct cgroup`` kptr that's already
-stored in a map using bpf_cgroup_kptr_get():
-
-.. kernel-doc:: kernel/bpf/helpers.c
- :identifiers: bpf_cgroup_kptr_get
-
-Here's an example of how it can be used:
-
-.. code-block:: c
-
- /* struct containing the struct task_struct kptr which is actually stored in the map. */
- struct __cgroups_kfunc_map_value {
- struct cgroup __kptr * cgroup;
- };
-
- /* The map containing struct __cgroups_kfunc_map_value entries. */
- struct {
- __uint(type, BPF_MAP_TYPE_HASH);
- __type(key, int);
- __type(value, struct __cgroups_kfunc_map_value);
- __uint(max_entries, 1);
- } __cgroups_kfunc_map SEC(".maps");
-
- /* ... */
-
- /**
- * A simple example tracepoint program showing how a
- * struct cgroup kptr that is stored in a map can
- * be acquired using the bpf_cgroup_kptr_get() kfunc.
- */
- SEC("tp_btf/cgroup_mkdir")
- int BPF_PROG(cgroup_kptr_get_example, struct cgroup *cgrp, const char *path)
- {
- struct cgroup *kptr;
- struct __cgroups_kfunc_map_value *v;
- s32 id = cgrp->self.id;
-
- /* Assume a cgroup kptr was previously stored in the map. */
- v = bpf_map_lookup_elem(&__cgroups_kfunc_map, &id);
- if (!v)
- return -ENOENT;
-
- /* Acquire a reference to the cgroup kptr that's already stored in the map. */
- kptr = bpf_cgroup_kptr_get(&v->cgroup);
- if (!kptr)
- /* If no cgroup was present in the map, it's because
- * we're racing with another CPU that removed it with
- * bpf_kptr_xchg() between the bpf_map_lookup_elem()
- * above, and our call to bpf_cgroup_kptr_get().
- * bpf_cgroup_kptr_get() internally safely handles this
- * race, and will return NULL if the task is no longer
- * present in the map by the time we invoke the kfunc.
- */
- return -EBUSY;
-
- /* Free the reference we just took above. Note that the
- * original struct cgroup kptr is still in the map. It will
- * be freed either at a later time if another context deletes
- * it from the map, or automatically by the BPF subsystem if
- * it's still present when the map is destroyed.
- */
- bpf_cgroup_release(kptr);
-
- return 0;
- }
-
-----
-
Other kfuncs available for interacting with ``struct cgroup *`` objects are
bpf_cgroup_ancestor() and bpf_cgroup_from_id(), allowing callers to access
the ancestor of a cgroup and find a cgroup by its ID, respectively. Both
--
2.40.0
Hello:
This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <[email protected]>:
On Mon, 10 Apr 2023 23:16:31 -0500 you wrote:
> struct cgroup is already an RCU-safe type in the verifier. We can
> therefore update bpf_cgroup_acquire() to be KF_RCU | KF_RET_NULL, and
> subsequently remove bpf_cgroup_kptr_get(). This patch does the first of
> these by updating bpf_cgroup_acquire() to be KF_RCU | KF_RET_NULL, and
> also updates selftests accordingly.
>
> Signed-off-by: David Vernet <[email protected]>
>
> [...]
Here is the summary with links:
- [bpf-next,1/3] bpf: Make bpf_cgroup_acquire() KF_RCU | KF_RET_NULL
https://git.kernel.org/bpf/bpf-next/c/1d71283987c7
- [bpf-next,2/3] bpf: Remove bpf_cgroup_kptr_get() kfunc
https://git.kernel.org/bpf/bpf-next/c/6499fe6edc4f
- [bpf-next,3/3] bpf,docs: Remove references to bpf_cgroup_kptr_get()
https://git.kernel.org/bpf/bpf-next/c/ec48599abee3
You are awesome, thank you!
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