bpf, cgroup: Fix invalid storage access after __cgroup_bpf_attach failed

A potential invalid storage access issue can occur after replacing a
cgroup bpf prog.

This occurs in the following scenario:
1. prog1 with storage is attached to a cgroup in multi-attach mode.
2. prog1 is replaced with prog2 using BPF_F_REPLACE in multi-attach
   mode, but fails midway (e.g. in bpf_trampoline_link_cgroup_shim or
   update_effective_progs).
3. A new prog3 is attached to the cgroup in multi-attach mode.

The reason is that __cgroup_bpf_attach overwrites pl->storage with the
new storage prior to attachment completion. When attachment fails
midway, the cleanup path calls bpf_cgroup_storages_free(new_storage) to
free the newly allocated storage, but fails to restore pl->storage back
to old_storage.

Consequently, the still-active prog1 holds invalid or dangling storage
pointers, leading to an invalid memory access when prog1 executes and
calls bpf_get_local_storage. Additionally, original pl->flags and
cgrp->bpf.flags[atype] are left unrestored.

Fix this by saving old_pl_flags, old_storage, and old_flags prior to the
update, and properly restoring all of them in the cleanup path on error.

Fixes: 7d9c3427894f ("bpf: Make cgroup storages shared between programs on the same cgroup")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/bpf/20260803013934.4036646-1-pulehui@huaweicloud.com

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index fb9357b64cad..d2da5063d8f8 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -813,8 +813,10 @@ static int __cgroup_bpf_attach(struct cgroup *cgrp,
 	struct bpf_prog *old_prog = NULL;
 	struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
 	struct bpf_cgroup_storage *new_storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
+	struct bpf_cgroup_storage *old_storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
 	struct bpf_prog *new_prog = prog ? : link->link.prog;
 	enum cgroup_bpf_attach_type atype;
+	u32 old_flags, old_pl_flags;
 	struct bpf_prog_list *pl;
 	struct hlist_head *progs;
 	int err;
@@ -865,6 +867,8 @@ static int __cgroup_bpf_attach(struct cgroup *cgrp,
 
 	if (pl) {
 		old_prog = pl->prog;
+		old_pl_flags = pl->flags;
+		bpf_cgroup_storages_assign(old_storage, pl->storage);
 	} else {
 		pl = kmalloc_obj(*pl);
 		if (!pl) {
@@ -884,6 +888,7 @@ static int __cgroup_bpf_attach(struct cgroup *cgrp,
 	pl->link = link;
 	pl->flags = flags;
 	bpf_cgroup_storages_assign(pl->storage, storage);
+	old_flags = cgrp->bpf.flags[atype];
 	cgrp->bpf.flags[atype] = saved_flags;
 
 	if (type == BPF_LSM_CGROUP) {
@@ -915,12 +920,15 @@ cleanup:
 	if (old_prog) {
 		pl->prog = old_prog;
 		pl->link = NULL;
+		pl->flags = old_pl_flags;
+		bpf_cgroup_storages_assign(pl->storage, old_storage);
 	}
 	bpf_cgroup_storages_free(new_storage);
 	if (!old_prog) {
 		hlist_del(&pl->node);
 		kfree(pl);
 	}
+	cgrp->bpf.flags[atype] = old_flags;
 	return err;
 }