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From:   Roman Gushchin <guro@fb.com>
To:     <netdev@vger.kernel.org>
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        Roman Gushchin <guro@fb.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>
Subject: [PATCH v2 bpf 3/5] bpf: bpf_prog_array_free() should take a generic non-rcu pointer
Date:   Fri, 13 Jul 2018 12:41:12 -0700
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bpf_prog_array_free() should take a generic non-rcu pointer
as an argument, as freeing the objects assumes that we're
holding an exclusive rights on it.

rcu_access_pointer() can be used to convert a __rcu pointer to
a generic pointer before passing it to bpf_prog_array_free(),
if necessary.

This patch eliminates the following sparse warning:
kernel/bpf/core.c:1556:9: warning: incorrect type in argument 1 (different address spaces)
kernel/bpf/core.c:1556:9:    expected struct callback_head *head
kernel/bpf/core.c:1556:9:    got struct callback_head [noderef] <asn:4>*<noident>

Fixes: 324bda9e6c5a ("bpf: multi program support for cgroup+bpf")
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
---
 drivers/media/rc/bpf-lirc.c |  6 +++---
 include/linux/bpf.h         |  2 +-
 kernel/bpf/cgroup.c         | 11 ++++++-----
 kernel/bpf/core.c           |  5 ++---
 kernel/trace/bpf_trace.c    |  8 ++++----
 5 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/drivers/media/rc/bpf-lirc.c b/drivers/media/rc/bpf-lirc.c
index fcfab6635f9c..509b262aa0dc 100644
--- a/drivers/media/rc/bpf-lirc.c
+++ b/drivers/media/rc/bpf-lirc.c
@@ -135,7 +135,7 @@ static int lirc_bpf_attach(struct rc_dev *rcdev, struct bpf_prog *prog)
 		goto unlock;
 
 	rcu_assign_pointer(raw->progs, new_array);
-	bpf_prog_array_free(old_array);
+	bpf_prog_array_free(rcu_access_pointer(old_array));
 
 unlock:
 	mutex_unlock(&ir_raw_handler_lock);
@@ -173,7 +173,7 @@ static int lirc_bpf_detach(struct rc_dev *rcdev, struct bpf_prog *prog)
 		goto unlock;
 
 	rcu_assign_pointer(raw->progs, new_array);
-	bpf_prog_array_free(old_array);
+	bpf_prog_array_free(rcu_access_pointer(old_array));
 unlock:
 	mutex_unlock(&ir_raw_handler_lock);
 	return ret;
@@ -204,7 +204,7 @@ void lirc_bpf_free(struct rc_dev *rcdev)
 	while (*progs)
 		bpf_prog_put(*progs++);
 
-	bpf_prog_array_free(rcdev->raw->progs);
+	bpf_prog_array_free(rcu_access_pointer(rcdev->raw->progs));
 }
 
 int lirc_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 943fb08d8287..329026baef6e 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -353,7 +353,7 @@ struct bpf_prog_array {
 };
 
 struct bpf_prog_array *bpf_prog_array_alloc(u32 prog_cnt, gfp_t flags);
-void bpf_prog_array_free(struct bpf_prog_array __rcu *progs);
+void bpf_prog_array_free(struct bpf_prog_array *progs);
 int bpf_prog_array_length(struct bpf_prog_array __rcu *progs);
 int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
 				__u32 __user *prog_ids, u32 cnt);
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index badabb0b435c..9ac0c9b51d0d 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -37,7 +37,8 @@ void cgroup_bpf_put(struct cgroup *cgrp)
 			kfree(pl);
 			static_branch_dec(&cgroup_bpf_enabled_key);
 		}
-		bpf_prog_array_free(cgrp->bpf.effective[type]);
+		bpf_prog_array_free(rcu_access_pointer(
+					    cgrp->bpf.effective[type]));
 	}
 }
 
@@ -139,7 +140,7 @@ static void activate_effective_progs(struct cgroup *cgrp,
 	/* free prog array after grace period, since __cgroup_bpf_run_*()
 	 * might be still walking the array
 	 */
-	bpf_prog_array_free(old_array);
+	bpf_prog_array_free(rcu_access_pointer(old_array));
 }
 
 /**
@@ -168,7 +169,7 @@ int cgroup_bpf_inherit(struct cgroup *cgrp)
 	return 0;
 cleanup:
 	for (i = 0; i < NR; i++)
-		bpf_prog_array_free(arrays[i]);
+		bpf_prog_array_free(rcu_access_pointer(arrays[i]));
 	return -ENOMEM;
 }
 
@@ -270,7 +271,7 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
 	css_for_each_descendant_pre(css, &cgrp->self) {
 		struct cgroup *desc = container_of(css, struct cgroup, self);
 
-		bpf_prog_array_free(desc->bpf.inactive);
+		bpf_prog_array_free(rcu_access_pointer(desc->bpf.inactive));
 		desc->bpf.inactive = NULL;
 	}
 
@@ -372,7 +373,7 @@ int __cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
 	css_for_each_descendant_pre(css, &cgrp->self) {
 		struct cgroup *desc = container_of(css, struct cgroup, self);
 
-		bpf_prog_array_free(desc->bpf.inactive);
+		bpf_prog_array_free(rcu_access_pointer(desc->bpf.inactive));
 		desc->bpf.inactive = NULL;
 	}
 
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 253aa8e79c7b..fdf961f70deb 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1548,10 +1548,9 @@ struct bpf_prog_array *bpf_prog_array_alloc(u32 prog_cnt, gfp_t flags)
 	return &empty_prog_array.hdr;
 }
 
-void bpf_prog_array_free(struct bpf_prog_array __rcu *progs)
+void bpf_prog_array_free(struct bpf_prog_array *progs)
 {
-	if (!progs ||
-	    progs == (struct bpf_prog_array __rcu *)&empty_prog_array.hdr)
+	if (!progs || progs == &empty_prog_array.hdr)
 		return;
 	kfree_rcu(progs, rcu);
 }
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 0ae6829804bc..5dace25d3088 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -995,8 +995,8 @@ int perf_event_attach_bpf_prog(struct perf_event *event,
 
 	/* set the new array to event->tp_event and set event->prog */
 	event->prog = prog;
-	rcu_assign_pointer(event->tp_event->prog_array, new_array);
-	bpf_prog_array_free(old_array);
+	rcu_swap_protected(event->tp_event->prog_array, new_array, 1);
+	bpf_prog_array_free(new_array);
 
 unlock:
 	mutex_unlock(&bpf_event_mutex);
@@ -1021,8 +1021,8 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
 	if (ret < 0) {
 		bpf_prog_array_delete_safe(old_array, event->prog);
 	} else {
-		rcu_assign_pointer(event->tp_event->prog_array, new_array);
-		bpf_prog_array_free(old_array);
+		rcu_swap_protected(event->tp_event->prog_array, new_array, 1);
+		bpf_prog_array_free(new_array);
 	}
 
 	bpf_prog_put(event->prog);
-- 
2.14.4