ata: libata-core: fix NULL pointer deref in ata_host_alloc_pinfo()

stable inclusion
from stable-4.19.249
commit a810bd5af06977a847d1f202b22d7defd5c62497
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5I4FP
CVE: NA

--------------------------------

[ Upstream commit bf476fe2 ]

In an unlikely (and probably wrong?) case that the 'ppi' parameter of
ata_host_alloc_pinfo() points to an array starting with a NULL pointer,
there's going to be a kernel oops as the 'pi' local variable won't get
reassigned from the initial value of NULL. Initialize 'pi' instead to
'&ata_dummy_port_info' to fix the possible kernel oops for good...

Found by Linux Verification Center (linuxtesting.org) with the SVACE static
analysis tool.
Signed-off-by: NSergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: NDamien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

drivers/ata/libata-core.c

@@ -6240,7 +6240,7 @@ struct ata_host *ata_host_alloc_pinfo(struct device *dev,
 				      const struct ata_port_info * const * ppi,
 				      int n_ports)
 {
-	const struct ata_port_info *pi;
+	const struct ata_port_info *pi = &ata_dummy_port_info;
 	struct ata_host *host;
 	int i, j;
 
@@ -6248,7 +6248,7 @@ struct ata_host *ata_host_alloc_pinfo(struct device *dev,
 	if (!host)
 		return NULL;
 
-	for (i = 0, j = 0, pi = NULL; i < host->n_ports; i++) {
+	for (i = 0, j = 0; i < host->n_ports; i++) {
 		struct ata_port *ap = host->ports[i];
 
 		if (ppi[j])