[PATCH 4/5] liveupdate: validate handover metadata before using it

[Oskar Gerlicz Kowalczuk <oskar@gerlicz.space>]

The handover restore path currently trusts counts, strings and
addresses copied from the previous kernel. A truncated or corrupted
handover can feed invalid header addresses, oversized counts,
unterminated names or impossible memfd folio layouts straight into
restore code.

That is dangerous because it can turn a bad handover into
out-of-bounds iteration, bogus phys_to_virt() translations or
inconsistent shmem state in the new kernel.

Add cheap sanity checks before consuming the metadata. Validate
session and file counts, require non-zero serialized pointers when
data is present, reject unterminated names, sanity-check FLB headers,
and make memfd_luo reject impossible folio indices and unsupported
flags.

Signed-off-by: Oskar Gerlicz Kowalczuk <oskar@gerlicz.space>
---
 kernel/liveupdate/luo_file.c    | 19 +++++++++++++++----
 kernel/liveupdate/luo_flb.c     | 14 ++++++++++++++
 kernel/liveupdate/luo_session.c | 16 ++++++++++++++++
 mm/memfd_luo.c                  | 26 ++++++++++++++++++++++++++
 4 files changed, 71 insertions(+), 4 deletions(-)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index cc0fd7e9c332..94d49255115d 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -765,10 +765,14 @@ int luo_file_deserialize(struct luo_file_set *file_set,
 	u64 i;
 	int err;
 
-	if (!file_set_ser->files) {
-		WARN_ON(file_set_ser->count);
-		return 0;
-	}
+	if (!file_set_ser->count)
+		return file_set_ser->files ? -EINVAL : 0;
+
+	if (!file_set_ser->files)
+		return -EINVAL;
+
+	if (file_set_ser->count > LUO_FILE_MAX)
+		return -EINVAL;
 
 	file_set->count = file_set_ser->count;
 	file_set->files = phys_to_virt(file_set_ser->files);
@@ -779,6 +783,13 @@ int luo_file_deserialize(struct luo_file_set *file_set,
 		bool handler_found = false;
 		struct luo_file *luo_file;
 
+		if (strnlen(file_ser[i].compatible,
+			    sizeof(file_ser[i].compatible)) ==
+		    sizeof(file_ser[i].compatible)) {
+			err = -EINVAL;
+			goto err_discard;
+		}
+
 		list_private_for_each_entry(fh, &luo_file_handler_list, list) {
 			if (!strcmp(fh->compatible, file_ser[i].compatible)) {
 				handler_found = true;
diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index f52e8114837e..3672cbf8e075 100644
--- a/kernel/liveupdate/luo_flb.c
+++ b/kernel/liveupdate/luo_flb.c
@@ -165,7 +165,14 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
 		return -ENODATA;
 
 	for (int i = 0; i < fh->header_ser->count; i++) {
+		if (strnlen(fh->ser[i].name, sizeof(fh->ser[i].name)) ==
+		    sizeof(fh->ser[i].name))
+			return -EINVAL;
+
 		if (!strcmp(fh->ser[i].name, flb->compatible)) {
+			if (!fh->ser[i].count)
+				return -EINVAL;
+
 			private->incoming.data = fh->ser[i].data;
 			private->incoming.count = fh->ser[i].count;
 			found = true;
@@ -609,7 +616,14 @@ int __init luo_flb_setup_incoming(void *fdt_in)
 	}
 
 	header_ser_pa = get_unaligned((u64 *)ptr);
+	if (!header_ser_pa) {
+		pr_err("FLB header address is missing\n");
+		return -EINVAL;
+	}
+
 	header_ser = phys_to_virt(header_ser_pa);
+	if (header_ser->pgcnt != LUO_FLB_PGCNT || header_ser->count > LUO_FLB_MAX)
+		return -EINVAL;
 
 	luo_flb_global.incoming.header_ser = header_ser;
 	luo_flb_global.incoming.ser = (void *)(header_ser + 1);
diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
index 77afa913d6c7..9a08e9794062 100644
--- a/kernel/liveupdate/luo_session.c
+++ b/kernel/liveupdate/luo_session.c
@@ -542,6 +542,11 @@ int __init luo_session_setup_incoming(void *fdt_in)
 	}
 
 	header_ser_pa = get_unaligned((u64 *)ptr);
+	if (!header_ser_pa) {
+		pr_err("Session header address is missing\n");
+		return -EINVAL;
+	}
+
 	header_ser = phys_to_virt(header_ser_pa);
 
 	luo_session_global.incoming.header_ser = header_ser;
@@ -565,9 +570,20 @@ int luo_session_deserialize(void)
 	if (!sh->active)
 		return 0;
 
+	if (sh->header_ser->count > LUO_SESSION_MAX) {
+		pr_warn("Invalid session count %llu\n", sh->header_ser->count);
+		return -EINVAL;
+	}
+
 	for (int i = 0; i < sh->header_ser->count; i++) {
 		struct luo_session *session;
 
+		if (strnlen(sh->ser[i].name, sizeof(sh->ser[i].name)) ==
+		    sizeof(sh->ser[i].name)) {
+			pr_warn("Session name is not NUL-terminated\n");
+			return -EINVAL;
+		}
+
 		session = luo_session_alloc(sh->ser[i].name);
 		if (IS_ERR(session)) {
 			pr_warn("Failed to allocate session [%s] during deserialization %pe\n",
diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c
index b8edb9f981d7..75f3f7226e6e 100644
--- a/mm/memfd_luo.c
+++ b/mm/memfd_luo.c
@@ -394,10 +394,15 @@ static int memfd_luo_retrieve_folios(struct file *file,
 {
 	struct inode *inode = file_inode(file);
 	struct address_space *mapping = inode->i_mapping;
+	u64 max_index = i_size_read(inode);
+	u64 prev_index = 0;
 	struct folio *folio;
 	int err = -EIO;
 	long i;
 
+	if (max_index)
+		max_index = (max_index - 1) >> PAGE_SHIFT;
+
 	for (i = 0; i < nr_folios; i++) {
 		const struct memfd_luo_folio_ser *pfolio = &folios_ser[i];
 		phys_addr_t phys;
@@ -407,6 +412,18 @@ static int memfd_luo_retrieve_folios(struct file *file,
 		if (!pfolio->pfn)
 			continue;
 
+		if (pfolio->flags &
+		    ~(MEMFD_LUO_FOLIO_DIRTY | MEMFD_LUO_FOLIO_UPTODATE)) {
+			err = -EINVAL;
+			goto put_folios;
+		}
+
+		if (pfolio->index > max_index ||
+		    (i && pfolio->index <= prev_index)) {
+			err = -EINVAL;
+			goto put_folios;
+		}
+
 		phys = PFN_PHYS(pfolio->pfn);
 		folio = kho_restore_folio(phys);
 		if (!folio) {
@@ -415,6 +432,7 @@ static int memfd_luo_retrieve_folios(struct file *file,
 			goto put_folios;
 		}
 		index = pfolio->index;
+		prev_index = index;
 		flags = pfolio->flags;
 
 		/* Set up the folio for insertion. */
@@ -486,6 +504,14 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)
 	if (!ser)
 		return -EINVAL;
 
+	if (!!ser->nr_folios != !!ser->folios.first.phys)
+		return -EINVAL;
+
+	if (ser->nr_folios &&
+	    (!ser->size ||
+	     ser->nr_folios > ((ser->size - 1) >> PAGE_SHIFT) + 1))
+		return -EINVAL;
+
 	file = memfd_alloc_file("", 0);
 	if (IS_ERR(file)) {
 		pr_err("failed to setup file: %pe\n", file);
-- 
2.53.0