[PATCH bpf-next] bpf: initialize storage pointers to NULL to prevent freeing garbage pointer

[PATCH bpf-next] bpf: initialize storage pointers to NULL to prevent freeing garbage pointer

[Andrii Nakryiko]

Local storage array isn't initialized, so if cgroup storage allocation fails
for BPF_CGROUP_STORAGE_SHARED, error handling code will attempt to free
uninitialized pointer for BPF_CGROUP_STORAGE_PERCPI storage type. Avoid this
by always initializing storage pointers to NULLs.

Fixes: 8bad74f9840f ("bpf: extend cgroup bpf core to allow multiple cgroup storage types")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 kernel/bpf/cgroup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 9a500fadbef5..b2bc4c335bb1 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -302,8 +302,8 @@ int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
 	u32 saved_flags = (flags & (BPF_F_ALLOW_OVERRIDE | BPF_F_ALLOW_MULTI));
 	struct list_head *progs = &cgrp->bpf.progs[type];
 	struct bpf_prog *old_prog = NULL;
-	struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE],
-		*old_storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {NULL};
+	struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
+	struct bpf_cgroup_storage *old_storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
 	struct bpf_prog_list *pl, *replace_pl = NULL;
 	enum bpf_cgroup_storage_type stype;
 	int err;
-- 
2.17.1

Re: [PATCH bpf-next] bpf: initialize storage pointers to NULL to prevent freeing garbage pointer

[Alexei Starovoitov]

On Mon, Mar 9, 2020 at 3:28 PM Andrii Nakryiko <andriin@fb.com> wrote:
>
> Local storage array isn't initialized, so if cgroup storage allocation fails
> for BPF_CGROUP_STORAGE_SHARED, error handling code will attempt to free
> uninitialized pointer for BPF_CGROUP_STORAGE_PERCPI storage type. Avoid this
> by always initializing storage pointers to NULLs.
>
> Fixes: 8bad74f9840f ("bpf: extend cgroup bpf core to allow multiple cgroup storage types")
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Applied to bpf tree and fixed typo in commit log.