[PATCH 5.6 049/106] cpumap: Avoid warning when CONFIG_DEBUG_PER_CPU_MAPS is enabled

[Greg Kroah-Hartman]

From: Toke HÃiland-JÃrgensen <toke@xxxxxxxxxx>

commit bc23d0e3f717ced21fbfacab3ab887d55e5ba367 upstream.

When the kernel is built with CONFIG_DEBUG_PER_CPU_MAPS, the cpumap code
can trigger a spurious warning if CONFIG_CPUMASK_OFFSTACK is also set. This
happens because in this configuration, NR_CPUS can be larger than
nr_cpumask_bits, so the initial check in cpu_map_alloc() is not sufficient
to guard against hitting the warning in cpumask_check().

Fix this by explicitly checking the supplied key against the
nr_cpumask_bits variable before calling cpu_possible().

Fixes: 6710e1126934 ("bpf: introduce new bpf cpu map type BPF_MAP_TYPE_CPUMAP")
Reported-by: Xiumei Mu <xmu@xxxxxxxxxx>
Signed-off-by: Toke HÃiland-JÃrgensen <toke@xxxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Tested-by: Xiumei Mu <xmu@xxxxxxxxxx>
Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Acked-by: Song Liu <songliubraving@xxxxxx>
Link: https://lore.kernel.org/bpf/20200416083120.453718-1-toke@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/bpf/cpumap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -469,7 +469,7 @@ static int cpu_map_update_elem(struct bp
 		return -EOVERFLOW;
 
 	/* Make sure CPU is a valid possible cpu */
-	if (!cpu_possible(key_cpu))
+	if (key_cpu >= nr_cpumask_bits || !cpu_possible(key_cpu))
 		return -ENODEV;
 
 	if (qsize == 0) {