PM: EM: Fix NULL pointer dereference when perf domain ID is not found

dev_energymodel_nl_get_perf_domains_doit() calls
em_perf_domain_get_by_id() but does not check the return value before
passing it to __em_nl_get_pd_size(). When a caller supplies a
non-existent perf domain ID, em_perf_domain_get_by_id() returns NULL,
and __em_nl_get_pd_size() immediately dereferences pd->cpus
(struct offset 0x30), causing a NULL pointer dereference.

The sister handler dev_energymodel_nl_get_perf_table_doit() already
handles this correctly via __em_nl_get_pd_table_id(), which returns
NULL and causes the caller to return -EINVAL. Add the same NULL check
in the get-perf-domains do handler.

Fixes: 380ff27 ("PM: EM: Add dump to get-perf-domains in the EM YNL spec")
Reported-by: Yi Lai <[email protected]>
Closes: https://lore.kernel.org/lkml/aXiySM79UYfk+ytd@ly-workstation/
Signed-off-by: Changwoo Min <[email protected]>
Cc: 6.19+ <[email protected]> # 6.19+
[ rjw: Subject and changelog edits ]
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: multics69

kernel/power/em_netlink.c

@@ -109,6 +109,8 @@ int dev_energymodel_nl_get_perf_domains_doit(struct sk_buff *skb,
 
 	id = nla_get_u32(info->attrs[DEV_ENERGYMODEL_A_PERF_DOMAIN_PERF_DOMAIN_ID]);
 	pd = em_perf_domain_get_by_id(id);
+	if (!pd)
+		return -EINVAL;
 
 	__em_nl_get_pd_size(pd, &msg_sz);
 	msg = genlmsg_new(msg_sz, GFP_KERNEL);