mm: krealloc: Fix MTE false alarm in __do_krealloc

This patch addresses an issue introduced by commit 1a83a716ec233 ("mm:
krealloc: consider spare memory for __GFP_ZERO") which causes MTE
(Memory Tagging Extension) to falsely report a slab-out-of-bounds error.

The problem occurs when zeroing out spare memory in __do_krealloc. The
original code only considered software-based KASAN and did not account
for MTE. It does not reset the KASAN tag before calling memset, leading
to a mismatch between the pointer tag and the memory tag, resulting
in a false positive.

Example of the error:
==================================================================
swapper/0: BUG: KASAN: slab-out-of-bounds in __memset+0x84/0x188
swapper/0: Write at addr f4ffff8005f0fdf0 by task swapper/0/1
swapper/0: Pointer tag: [f4], memory tag: [fe]
swapper/0:
swapper/0: CPU: 4 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.12.
swapper/0: Hardware name: MT6991(ENG) (DT)
swapper/0: Call trace:
swapper/0:  dump_backtrace+0xfc/0x17c
swapper/0:  show_stack+0x18/0x28
swapper/0:  dump_stack_lvl+0x40/0xa0
swapper/0:  print_report+0x1b8/0x71c
swapper/0:  kasan_report+0xec/0x14c
swapper/0:  __do_kernel_fault+0x60/0x29c
swapper/0:  do_bad_area+0x30/0xdc
swapper/0:  do_tag_check_fault+0x20/0x34
swapper/0:  do_mem_abort+0x58/0x104
swapper/0:  el1_abort+0x3c/0x5c
swapper/0:  el1h_64_sync_handler+0x80/0xcc
swapper/0:  el1h_64_sync+0x68/0x6c
swapper/0:  __memset+0x84/0x188
swapper/0:  btf_populate_kfunc_set+0x280/0x3d8
swapper/0:  __register_btf_kfunc_id_set+0x43c/0x468
swapper/0:  register_btf_kfunc_id_set+0x48/0x60
swapper/0:  register_nf_nat_bpf+0x1c/0x40
swapper/0:  nf_nat_init+0xc0/0x128
swapper/0:  do_one_initcall+0x184/0x464
swapper/0:  do_initcall_level+0xdc/0x1b0
swapper/0:  do_initcalls+0x70/0xc0
swapper/0:  do_basic_setup+0x1c/0x28
swapper/0:  kernel_init_freeable+0x144/0x1b8
swapper/0:  kernel_init+0x20/0x1a8
swapper/0:  ret_from_fork+0x10/0x20
==================================================================

Fixes: 1a83a716ec233 ("mm: krealloc: consider spare memory for __GFP_ZERO")
Signed-off-by: Qun-Wei Lin <qun-wei.lin@mediatek.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 3d26c257ed8b57c336ec5c38d4bbd5f5e51d50ff..552b92dfdac775c3aee9a1bb116c85ca527835cc 100644 (file)
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1209,7 +1209,7 @@ __do_krealloc(const void *p, size_t new_size, gfp_t flags)
                /* Zero out spare memory. */
                if (want_init_on_alloc(flags)) {
                        kasan_disable_current();
-                       memset((void *)p + new_size, 0, ks - new_size);
+                       memset(kasan_reset_tag(p) + new_size, 0, ks - new_size);
                        kasan_enable_current();
                }