6.18-stable review patch. If anyone has any objections, please let me know.
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From: Deepanshu Kartikey kartikey406@gmail.com
commit 53ca00a19d345197a37a1bf552e8d1e7b091666c upstream.
When CONFIG_SLUB_TINY is enabled, kfree_nolock() calls kasan_slab_free() before defer_free(). On ARM64 with MTE (Memory Tagging Extension), kasan_slab_free() poisons the memory and changes the tag from the original (e.g., 0xf3) to a poison tag (0xfe).
When defer_free() then tries to write to the freed object to build the deferred free list via llist_add(), the pointer still has the old tag, causing a tag mismatch and triggering a KASAN use-after-free report:
BUG: KASAN: slab-use-after-free in defer_free+0x3c/0xbc mm/slub.c:6537 Write at addr f3f000000854f020 by task kworker/u8:6/983 Pointer tag: [f3], memory tag: [fe]
Fix this by calling kasan_reset_tag() before accessing the freed memory. This is safe because defer_free() is part of the allocator itself and is expected to manipulate freed memory for bookkeeping purposes.
Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") Cc: stable@vger.kernel.org Reported-by: syzbot+7a25305a76d872abcfa1@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=7a25305a76d872abcfa1 Tested-by: syzbot+7a25305a76d872abcfa1@syzkaller.appspotmail.com Signed-off-by: Deepanshu Kartikey kartikey406@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org Link: https://patch.msgid.link/20251210022024.3255826-1-kartikey406@gmail.com Signed-off-by: Vlastimil Babka vbabka@suse.cz Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/slub.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/mm/slub.c +++ b/mm/slub.c @@ -6509,6 +6509,8 @@ static void defer_free(struct kmem_cache
guard(preempt)();
+ head = kasan_reset_tag(head); + df = this_cpu_ptr(&defer_free_objects); if (llist_add(head + s->offset, &df->objects)) irq_work_queue(&df->work);