The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 59090e479ac78ae18facd4c58eb332562a23020e # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024100708-unhidden-unscathed-7372@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

59090e479ac7 ("mm, slub: avoid zeroing kmalloc redzone") 8f828aa48812 ("mm/slub: avoid zeroing outside-object freepointer for single free") 2d5524635b00 ("slub, kasan: improve interaction of KASAN and slub_debug poisoning")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 59090e479ac78ae18facd4c58eb332562a23020e Mon Sep 17 00:00:00 2001 From: Peng Fan peng.fan@nxp.com Date: Thu, 29 Aug 2024 11:29:11 +0800 Subject: [PATCH] mm, slub: avoid zeroing kmalloc redzone

Since 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 a redzone. However with init_on_free=1 we clear the full object->size, including the redzone.

Additionally we clear the object metadata, including the stored orig_size, making it zero, which makes check_object() treat the whole object as a redzone.

These issues lead to the following BUG report with "slub_debug=FUZ init_on_free=1":

[ 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") Cc: stable@vger.kernel.org Reviewed-by: Feng Tang feng.tang@intel.com Acked-by: David Rientjes rientjes@google.com Signed-off-by: Peng Fan peng.fan@nxp.com Signed-off-by: Vlastimil Babka vbabka@suse.cz

diff --git a/mm/slub.c b/mm/slub.c index 60004bfc2dc2..d52c88f29f69 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -756,6 +756,50 @@ static inline bool slab_update_freelist(struct kmem_cache *s, struct slab *slab, return false; }

+/* + * kmalloc caches has fixed sizes (mostly power of 2), and kmalloc() API + * family will round up the real request size to these fixed ones, so + * there could be an extra area than what is requested. Save the original + * request size in the meta data area, for better debug and sanity check. + */ +static inline void set_orig_size(struct kmem_cache *s, + void *object, unsigned int orig_size) +{ + void *p = kasan_reset_tag(object); + unsigned int kasan_meta_size; + + if (!slub_debug_orig_size(s)) + return; + + /* + * KASAN can save its free meta data inside of the object at offset 0. + * If this meta data size is larger than 'orig_size', it will overlap + * the data redzone in [orig_size+1, object_size]. Thus, we adjust + * 'orig_size' to be as at least as big as KASAN's meta data. + */ + kasan_meta_size = kasan_metadata_size(s, true); + if (kasan_meta_size > orig_size) + orig_size = kasan_meta_size; + + p += get_info_end(s); + p += sizeof(struct track) * 2; + + *(unsigned int *)p = orig_size; +} + +static inline unsigned int get_orig_size(struct kmem_cache *s, void *object) +{ + void *p = kasan_reset_tag(object); + + if (!slub_debug_orig_size(s)) + return s->object_size; + + p += get_info_end(s); + p += sizeof(struct track) * 2; + + return *(unsigned int *)p; +} + #ifdef CONFIG_SLUB_DEBUG static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)]; static DEFINE_SPINLOCK(object_map_lock); @@ -985,50 +1029,6 @@ static void print_slab_info(const struct slab *slab) &slab->__page_flags); }

-/* - * kmalloc caches has fixed sizes (mostly power of 2), and kmalloc() API - * family will round up the real request size to these fixed ones, so - * there could be an extra area than what is requested. Save the original - * request size in the meta data area, for better debug and sanity check. - */ -static inline void set_orig_size(struct kmem_cache *s, - void *object, unsigned int orig_size) -{ - void *p = kasan_reset_tag(object); - unsigned int kasan_meta_size; - - if (!slub_debug_orig_size(s)) - return; - - /* - * KASAN can save its free meta data inside of the object at offset 0. - * If this meta data size is larger than 'orig_size', it will overlap - * the data redzone in [orig_size+1, object_size]. Thus, we adjust - * 'orig_size' to be as at least as big as KASAN's meta data. - */ - kasan_meta_size = kasan_metadata_size(s, true); - if (kasan_meta_size > orig_size) - orig_size = kasan_meta_size; - - p += get_info_end(s); - p += sizeof(struct track) * 2; - - *(unsigned int *)p = orig_size; -} - -static inline unsigned int get_orig_size(struct kmem_cache *s, void *object) -{ - void *p = kasan_reset_tag(object); - - if (!slub_debug_orig_size(s)) - return s->object_size; - - p += get_info_end(s); - p += sizeof(struct track) * 2; - - return *(unsigned int *)p; -} - void skip_orig_size_check(struct kmem_cache *s, const void *object) { set_orig_size(s, (void *)object, s->object_size); @@ -1894,7 +1894,6 @@ static inline void inc_slabs_node(struct kmem_cache *s, int node, int objects) {} static inline void dec_slabs_node(struct kmem_cache *s, int node, int objects) {} - #ifndef CONFIG_SLUB_TINY static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab, void **freelist, void *nextfree) @@ -2239,14 +2238,21 @@ 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);