From f58191bb7ce796a37260ae9c8a35ecc27246f66f Mon Sep 17 00:00:00 2001 From: Peng Fan Date: Fri, 23 Aug 2024 14:24:15 +0800 Subject: [PATCH] mm, slub: avoid zeroing kmalloc redzone With commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested"), setting orig_size treats the wasted space (object_size - orig_size) as redzones. But (in check_object()) when orig_size is set to zero, the entire object is perceived as a redzone. To a valid allocated kmalloc space, when init_on_free=1, the wasted space and the orig_size should not be cleared to 0, otherwise there will be kernel dump: [ 0.000000] ============================================================================= [ 0.000000] BUG kmalloc-8 (Not tainted): kmalloc Redzone overwritten [ 0.000000] ----------------------------------------------------------------------------- [ 0.000000] [ 0.000000] 0xffff000010032858-0xffff00001003285f @offset=2136. First byte 0x0 instead of 0xcc [ 0.000000] FIX kmalloc-8: Restoring kmalloc Redzone 0xffff000010032858-0xffff00001003285f=0xcc [ 0.000000] Slab 0xfffffdffc0400c80 objects=36 used=23 fp=0xffff000010032a18 flags=0x3fffe0000000200(workingset|node=0|zone=0|lastcpupid=0x1ffff) [ 0.000000] Object 0xffff000010032858 @offset=2136 fp=0xffff0000100328c8 [ 0.000000] [ 0.000000] Redzone ffff000010032850: cc cc cc cc cc cc cc cc ........ [ 0.000000] Object ffff000010032858: cc cc cc cc cc cc cc cc ........ [ 0.000000] Redzone ffff000010032860: cc cc cc cc cc cc cc cc ........ [ 0.000000] Padding ffff0000100328b4: 00 00 00 00 00 00 00 00 00 00 00 00 ............ [ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.11.0-rc3-next-20240814-00004-g61844c55c3f4 #144 [ 0.000000] Hardware name: NXP i.MX95 19X19 board (DT) [ 0.000000] Call trace: [ 0.000000] dump_backtrace+0x90/0xe8 [ 0.000000] show_stack+0x18/0x24 [ 0.000000] dump_stack_lvl+0x74/0x8c [ 0.000000] dump_stack+0x18/0x24 [ 0.000000] print_trailer+0x150/0x218 [ 0.000000] check_object+0xe4/0x454 [ 0.000000] free_to_partial_list+0x2f8/0x5ec To address the issue, use orig_size to clear the used area. And restore the value of orig_size after clear the remaining area. When CONFIG_SLUB_DEBUG not defined, (get_orig_size()' directly returns s->object_size. So when using memset to init the area, the size can simply be orig_size, as orig_size returns object_size when CONFIG_SLUB_DEBUG not enabled. And orig_size can never be bigger than object_size. Fixes: 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested") Signed-off-by: Peng Fan --- mm/slub.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index b6b947596e269b..d9f659b97701ca 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1895,6 +1895,15 @@ static inline void inc_slabs_node(struct kmem_cache *s, int node, static inline void dec_slabs_node(struct kmem_cache *s, int node, int objects) {} +static inline unsigned int get_orig_size(struct kmem_cache *s, void *object) +{ + return s->object_size; +} + +static inline void set_orig_size(struct kmem_cache *s, void *object, + unsigned int orig_size) +{} + #ifndef CONFIG_SLUB_TINY static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab, void **freelist, void *nextfree) @@ -2286,14 +2295,21 @@ bool slab_free_hook(struct kmem_cache *s, void *x, bool init, */ if (unlikely(init)) { int rsize; - unsigned int inuse; + unsigned int inuse, orig_size; inuse = get_info_end(s); + orig_size = get_orig_size(s, x); if (!kasan_has_integrated_init()) - memset(kasan_reset_tag(x), 0, s->object_size); + memset(kasan_reset_tag(x), 0, orig_size); rsize = (s->flags & SLAB_RED_ZONE) ? s->red_left_pad : 0; memset((char *)kasan_reset_tag(x) + inuse, 0, s->size - inuse - rsize); + /* + * Restore orig_size, otherwize kmalloc redzone overwritten + * would be reported + */ + set_orig_size(s, x, orig_size); + } /* KASAN might put x into memory quarantine, delaying its reuse. */ return !kasan_slab_free(s, x, init, still_accessible);