netdevsim: Zero-initialize memory for new map's value in function nsim_bpf_map_alloc

ANBZ: torvalds#415

commit 4812217 upstream

Zero-initialize memory for new map's value in function nsim_bpf_map_alloc
since it may cause a potential kernel information leak issue, as follows:
1. nsim_bpf_map_alloc calls nsim_map_alloc_elem to allocate elements for
a new map.
2. nsim_map_alloc_elem uses kmalloc to allocate map's value, but doesn't
zero it.
3. A user application can use IOCTL BPF_MAP_LOOKUP_ELEM to get specific
element's information in the map.
4. The kernel function map_lookup_elem will call bpf_map_copy_value to get
the information allocated at step-2, then use copy_to_user to copy to the
user buffer.
This can only leak information for an array map.

Fixes: 395cacb ("netdevsim: bpf: support fake map offload")
Suggested-by: Jakub Kicinski <[email protected]>
Acked-by: Jakub Kicinski <[email protected]>
Signed-off-by: Haimin Zhang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Fixes: CVE-2021-4135
Signed-off-by: Qiao Ma <[email protected]>
Acked-by: Tony Lu <[email protected]>

Author: Haimin Zhang

drivers/net/netdevsim/bpf.c

@@ -493,6 +493,7 @@ nsim_bpf_map_alloc(struct netdevsim *ns, struct bpf_offloaded_map *offmap)
 				goto err_free;
 			key = nmap->entry[i].key;
 			*key = i;
+			memset(nmap->entry[i].value, 0, offmap->map.value_size);
 		}
 	}