bpf: Ensure unit_size is matched with slab cache object size

JIRA: https://issues.redhat.com/browse/RHEL-10691

commit c930472552022bd09aab3cd946ba3f243070d5c7
Author: Hou Tao <houtao1@huawei.com>
Date:   Fri Sep 8 21:39:22 2023 +0800

    bpf: Ensure unit_size is matched with slab cache object size

    Add extra check in bpf_mem_alloc_init() to ensure the unit_size of
    bpf_mem_cache is matched with the object_size of underlying slab cache.
    If these two sizes are unmatched, print a warning once and return
    -EINVAL in bpf_mem_alloc_init(), so the mismatch can be found early and
    the potential issue can be prevented.

    Suggested-by: Alexei Starovoitov <ast@kernel.org>
    Signed-off-by: Hou Tao <houtao1@huawei.com>
    Link: https://lore.kernel.org/r/20230908133923.2675053-4-houtao@huaweicloud.com
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

kernel/bpf/memalloc.c

@@ -486,6 +486,24 @@ static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
 	alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu), false);
 }
 
+static int check_obj_size(struct bpf_mem_cache *c, unsigned int idx)
+{
+	struct llist_node *first;
+	unsigned int obj_size;
+
+	first = c->free_llist.first;
+	if (!first)
+		return 0;
+
+	obj_size = ksize(first);
+	if (obj_size != c->unit_size) {
+		WARN_ONCE(1, "bpf_mem_cache[%u]: unexpected object size %u, expect %u\n",
+			  idx, obj_size, c->unit_size);
+		return -EINVAL;
+	}
+	return 0;
+}
+
 /* When size != 0 bpf_mem_cache for each cpu.
  * This is typical bpf hash map use case when all elements have equal size.
  *
@@ -496,10 +514,10 @@ static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
 int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 {
 	static u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
+	int cpu, i, err, unit_size, percpu_size = 0;
 	struct bpf_mem_caches *cc, __percpu *pcc;
 	struct bpf_mem_cache *c, __percpu *pc;
 	struct obj_cgroup *objcg = NULL;
-	int cpu, i, unit_size, percpu_size = 0;
 
 	if (size) {
 		pc = __alloc_percpu_gfp(sizeof(*pc), 8, GFP_KERNEL);
@@ -537,6 +555,7 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 	pcc = __alloc_percpu_gfp(sizeof(*cc), 8, GFP_KERNEL);
 	if (!pcc)
 		return -ENOMEM;
+	err = 0;
 #ifdef CONFIG_MEMCG_KMEM
 	objcg = get_obj_cgroup_from_current();
 #endif
@@ -557,10 +576,20 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 			if (i != bpf_mem_cache_idx(c->unit_size))
 				continue;
 			prefill_mem_cache(c, cpu);
+			err = check_obj_size(c, i);
+			if (err)
+				goto out;
 		}
 	}
+
+out:
 	ma->caches = pcc;
-	return 0;
+	/* refill_work is either zeroed or initialized, so it is safe to
+	 * call irq_work_sync().
+	 */
+	if (err)
+		bpf_mem_alloc_destroy(ma);
+	return err;
 }
 
 static void drain_mem_cache(struct bpf_mem_cache *c)