[PATCH 1/1] mm/slab_common: reject zero object_size before calculate_alignment

[Longlong Xia]

From: Longlong Xia <xialonglong@xxxxxxxxxx>

calculate_alignment() with SLAB_HWCACHE_ALIGN halves ralign in a
while (size <= ralign / 2) loop. When size is 0, ralign eventually
reaches 0 and the condition stays true indefinitely, hanging the
kernel.

kmem_cache_sanity_check() rejected size > KMALLOC_MAX_SIZE but not
size == 0, and the sanity check is compiled out without
CONFIG_DEBUG_VM. Add a !object_size check in
__kmem_cache_create_args(), which is always compiled, and add !size
to the DEBUG_VM sanity check for diagnostics.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Longlong Xia <xialonglong@xxxxxxxxxx>
---
 mm/slab_common.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 657fd75776ea..209fe838fe71 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -102,7 +102,7 @@ static bool kmem_cache_is_duplicate_name(const char *name)
 
 static int kmem_cache_sanity_check(const char *name, unsigned int size)
 {
-	if (!name || in_interrupt() || size > KMALLOC_MAX_SIZE) {
+	if (!name || in_interrupt() || !size || size > KMALLOC_MAX_SIZE) {
 		pr_err("kmem_cache_create(%s) integrity check failed\n", name);
 		return -EINVAL;
 	}
@@ -354,7 +354,7 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
 		goto out_unlock;
 	}
 
-	if (flags & ~SLAB_FLAGS_PERMITTED) {
+	if (!object_size || flags & ~SLAB_FLAGS_PERMITTED) {
 		err = -EINVAL;
 		goto out_unlock;
 	}
-- 
2.43.0