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bpf: Make bpf_cgroup_acquire() KF_RCU | KF_RET_NULL

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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 <void@manifault.com>
Link: https://lore.kernel.org/r/20230411041633.179404-1-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
David Vernet 2023-04-10 23:16:31 -05:00 committed by Alexei Starovoitov
parent 10fd5f70c3
commit 1d71283987
4 changed files with 40 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
kernel/bpf/helpers.c
View file

@ -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)

5
tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
View file

@ -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);

35
tools/testing/selftests/bpf/progs/cgrp_kfunc_failure.c
View file

@ -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);

5
tools/testing/selftests/bpf/progs/cgrp_kfunc_success.c
View file

@ -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;
}