[PATCH 2/3] bootstd: Probe bootmeth devices for bootmeths env var

[Sam Protsenko]

Specifying efi_mgr in 'bootmeths' environment variable leads to NULL
pointer dereference when 'bootflow scan' is executed, with call trace
like this:

    priv->fake_dev // NULL pointer dereference
    .read_bootflow = efi_mgr_read_bootflow()
    bootmeth_get_bootflow()
    bootflow_check()
    bootflow_scan_first()
    do_bootflow_scan()
    'bootflow scan -l'

That happens because in case when 'bootmeths' env var is defined the
bootmeth_efi_mgr driver is not probed, and the memory for its private
data isn't allocated by .priv_auto. In case when 'bootmeths' env var is
not defined, the std->bootmeth_count is 0, and the execution flow in
bootmeth_setup_iter_order() takes "no ordering" path, which in turn runs
uclass_get_device_by_seq() -> ... -> device_probe(), so issue isn't
present there. But when 'bootmeths' is defined and contains efi_mgr, the
std->bootmeth_count > 0, so bootmeth_setup_iter_order() follows the "we
have an ordering" path, where devices are not probed. In other words:

    'bootmeths' defined           'bootmeths' not defined
    --------------------------------------------------------
    priv == NULL                    priv != NULL
         ^                                ^
         |                        device_alloc_priv()
     no probe                     device_of_to_plat()
         ^                        device_probe()
         |                        uclass_get_device_tail()
    dev = order[i]                uclass_get_device_by_seq()
         ^                                ^
         | have an ordering               | no ordering
         +----------------+---------------+
                          |
             bootmeth_setup_iter_order()
             bootflow_scan_first()
             do_bootflow_scan()

Add an explicit device_probe() call in "we have an ordering" case to fix
the issue.

Fixes: c627cfc14c08 ("bootstd: Allow scanning for global bootmeths separately")
Signed-off-by: Sam Protsenko <semen.protsenko at linaro.org>
---
 boot/bootmeth-uclass.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/boot/bootmeth-uclass.c b/boot/bootmeth-uclass.c
index ff36da78d5a1..049389403191 100644
--- a/boot/bootmeth-uclass.c
+++ b/boot/bootmeth-uclass.c
@@ -11,6 +11,7 @@
 #include <bootmeth.h>
 #include <bootstd.h>
 #include <dm.h>
+#include <dm/device-internal.h>
 #include <env_internal.h>
 #include <fs.h>
 #include <malloc.h>
@@ -146,6 +147,12 @@ int bootmeth_setup_iter_order(struct bootflow_iter *iter, bool include_global)
 				struct bootmeth_uc_plat *ucp;
 				bool is_global;
 
+				ret = device_probe(dev);
+				if (ret) {
+					ret = log_msg_ret("probe", ret);
+					goto err_order;
+				}
+
 				ucp = dev_get_uclass_plat(dev);
 				is_global = ucp->flags &
 					BOOTMETHF_GLOBAL;
-- 
2.39.5