[PATCH v2] mm/slub: preserve original size in _kmalloc_nolock_noprof retry path

[hu.shengming]

From: Shengming Hu <hu.shengming@xxxxxxxxxx>

_kmalloc_nolock_noprof() retries from the next kmalloc bucket when the
initial allocation fails. The retry currently reuses `size` as the
bucket selector and overwrites it with s->object_size + 1.

That value is later passed as the original allocation size to
__slab_alloc_node(), slab_post_alloc_hook() and kasan_kmalloc(). On a
successful retry this makes KASAN/slub-debug observe the retry bucket
selector rather than the caller requested size, potentially widening the
valid kmalloc range and hiding overflows.

Keep the caller requested size separately as orig_size and pass it to
the allocation/debug/KASAN paths. Continue using `size` as the retry cache
selector.

Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock()")
Signed-off-by: Shengming Hu <hu.shengming@xxxxxxxxxx>
---
Changes in v2:
- Use an explicit orig_size variable instead of bucket_size, as suggested
  by Harry and Vlastimil.
- Link to v1: https://lore.kernel.org/all/20260603211011530GqLSXP_rgcuQdR47IGQLL@xxxxxxxxxx/

---
 mm/slub.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 67abbbf68fc1..7e1a1fe5daaa 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5350,6 +5350,7 @@ EXPORT_SYMBOL(__kmalloc_noprof);
 void *_kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_flags, int node)
 {
 	gfp_t alloc_gfp = __GFP_NOWARN | __GFP_NOMEMALLOC | gfp_flags;
+	size_t orig_size = size;
 	struct kmem_cache *s;
 	bool can_retry = true;
 	void *ret;
@@ -5398,7 +5399,7 @@ void *_kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_flags, in
 	 * kfence_alloc. Hence call __slab_alloc_node() (at most twice)
 	 * and slab_post_alloc_hook() directly.
 	 */
-	ret = __slab_alloc_node(s, alloc_gfp, node, _RET_IP_, size);
+	ret = __slab_alloc_node(s, alloc_gfp, node, _RET_IP_, orig_size);

 	/*
 	 * It's possible we failed due to trylock as we preempted someone with
@@ -5422,9 +5423,9 @@ void *_kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_flags, in
 success:
 	maybe_wipe_obj_freeptr(s, ret);
 	slab_post_alloc_hook(s, NULL, alloc_gfp, 1, &ret,
-			     slab_want_init_on_alloc(alloc_gfp, s), size);
+			     slab_want_init_on_alloc(alloc_gfp, s), orig_size);

-	ret = kasan_kmalloc(s, ret, size, alloc_gfp);
+	ret = kasan_kmalloc(s, ret, orig_size, alloc_gfp);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(_kmalloc_nolock_noprof);
-- 
2.25.1