[PATCH v5 1/3] mm/memfd_luo: validate serialized_data before conversion

[Tarun Sahu <tarunsahu@google.com>]

In memfd_luo_finish() and memfd_luo_retrieve(), phys_to_virt() was called
on args->serialized_data before checking if the physical address is valid.
Since physical address 0 does not map to virtual NULL (due to direct
mapping offsets), the subsequent check 'if (!ser)' was ineffective at
catching a missing serialized_data, leading to unsafe dereferences later.

Validate that args->serialized_data is non-zero before calling
phys_to_virt().

Fixes: b3749f174d68 ("mm: memfd_luo: allow preserving memfd")
Signed-off-by: Tarun Sahu <tarunsahu@google.com>
---
 mm/memfd_luo.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c
index 59de210bee5f..10f3983b0060 100644
--- a/mm/memfd_luo.c
+++ b/mm/memfd_luo.c
@@ -397,10 +397,11 @@ static void memfd_luo_finish(struct liveupdate_file_op_args *args)
 	if (args->retrieve_status)
 		return;
 
-	ser = phys_to_virt(args->serialized_data);
-	if (!ser)
+	if (!args->serialized_data)
 		return;
 
+	ser = phys_to_virt(args->serialized_data);
+
 	if (ser->nr_folios) {
 		folios_ser = kho_restore_vmalloc(&ser->folios);
 		if (!folios_ser)
@@ -522,10 +523,11 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)
 	struct file *file;
 	int err;
 
-	ser = phys_to_virt(args->serialized_data);
-	if (!ser)
+	if (!args->serialized_data)
 		return -EINVAL;
 
+	ser = phys_to_virt(args->serialized_data);
+
 	/* Make sure the file only has seals supported by this version. */
 	if (ser->seals & ~MEMFD_LUO_ALL_SEALS) {
 		err = -EOPNOTSUPP;
-- 
2.55.0.rc0.786.g65d90a0328-goog