IB/core: Fix potential NULL pointer dereference in pkey cache

The IB core pkey cache is populated by procedure ib_cache_update().
Initially, the pkey cache pointer is NULL. ib_cache_update allocates a
buffer and populates it with the device's pkeys, via repeated calls to
procedure ib_query_pkey().

If there is a failure in populating the pkey buffer via ib_query_pkey(),
ib_cache_update does not replace the old pkey buffer cache with the
updated one -- it leaves the old cache as is.

Since initially the pkey buffer cache is NULL, when calling
ib_cache_update the first time, a failure in ib_query_pkey() will cause
the pkey buffer cache pointer to remain NULL.

In this situation, any calls subsequent to ib_get_cached_pkey(),
ib_find_cached_pkey(), or ib_find_cached_pkey_exact() will try to
dereference the NULL pkey cache pointer, causing a kernel panic.

Fix this by checking the ib_cache_update() return value.

Fixes: 8faea9f ("RDMA/cache: Move the cache per-port data into the main ib_port_data")
Fixes: 1da177e ("Linux-2.6.12-rc2")
Link: https://lore.kernel.org/r/20200507071012.100594-1-leon@kernel.org
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/cache.c

@@ -1553,8 +1553,11 @@ int ib_cache_setup_one(struct ib_device *device)
 	if (err)
 		return err;
 
-	rdma_for_each_port (device, p)
-		ib_cache_update(device, p, true);
+	rdma_for_each_port (device, p) {
+		err = ib_cache_update(device, p, true);
+		if (err)
+			return err;
+	}
 
 	return 0;
 }