[syzbot] [bpf?] KASAN: slab-use-after-free Write in defer_free

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 559e608c4655 Merge tag 'ntfs3_for_6.19' of https://github...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1080b192580000
kernel config: https://syzkaller.appspot.com/x/.config?x=35a67601c980c167
dashboard link: https://syzkaller.appspot.com/bug?extid=7a25305a76d872abcfa1
compiler: aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1574b01a580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16a33cc2580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/fa3fbcfdac58/non_bootable_disk-559e608c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5ff565203729/vmlinux-559e608c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/28d6e57737b9/Image-559e608c.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7a2530...@syzkaller.appspotmail.com

==================================================================
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]

CPU: 0 UID: 0 PID: 983 Comm: kworker/u8:6 Not tainted syzkaller #0 PREEMPT
Hardware name: linux,dummy-virt (DT)
Workqueue: events_unbound bpf_map_free_deferred
Call trace:
show_stack+0x18/0x24 arch/arm64/kernel/stacktrace.c:499 (C)
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x78/0x90 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0x108/0x61c mm/kasan/report.c:482
kasan_report+0x88/0xac mm/kasan/report.c:595
report_tag_fault arch/arm64/mm/fault.c:330 [inline]
do_tag_recovery arch/arm64/mm/fault.c:342 [inline]
__do_kernel_fault+0x170/0x1c8 arch/arm64/mm/fault.c:384
do_bad_area+0x68/0x78 arch/arm64/mm/fault.c:484
do_tag_check_fault+0x34/0x44 arch/arm64/mm/fault.c:857
do_mem_abort+0x44/0x94 arch/arm64/mm/fault.c:933
el1_abort+0x44/0x68 arch/arm64/kernel/entry-common.c:303
el1h_64_sync_handler+0x50/0xac arch/arm64/kernel/entry-common.c:437
el1h_64_sync+0x6c/0x70 arch/arm64/kernel/entry.S:591
defer_free+0x3c/0xbc mm/slub.c:6537 (P)
do_slab_free mm/slub.c:6619 [inline]
kfree_nolock+0x1a0/0x1d4 mm/slub.c:6930
range_tree_destroy+0x74/0x90 kernel/bpf/range_tree.c:253
arena_map_free+0x64/0x90 kernel/bpf/arena.c:196
bpf_map_free kernel/bpf/syscall.c:894 [inline]
bpf_map_free_deferred+0x70/0x180 kernel/bpf/syscall.c:921
process_one_work+0x178/0x2cc kernel/workqueue.c:3257
process_scheduled_works kernel/workqueue.c:3340 [inline]
worker_thread+0x24c/0x354 kernel/workqueue.c:3421
kthread+0x130/0x1fc kernel/kthread.c:463
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860

Allocated by task 3570:
kasan_save_stack+0x3c/0x64 mm/kasan/common.c:56
save_stack_info+0x40/0x158 mm/kasan/tags.c:106
kasan_save_alloc_info+0x14/0x20 mm/kasan/tags.c:142
poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
poison_kmalloc_redzone mm/kasan/common.c:373 [inline]
__kasan_kmalloc+0xb4/0xb8 mm/kasan/common.c:417
kasan_kmalloc include/linux/kasan.h:262 [inline]
kmalloc_nolock_noprof+0x1dc/0x4fc mm/slub.c:5751
range_tree_set+0x644/0x778 kernel/bpf/range_tree.c:237
arena_map_alloc+0x11c/0x17c kernel/bpf/arena.c:141
map_create+0x19c/0xa98 kernel/bpf/syscall.c:1514
__sys_bpf+0x348/0x1a88 kernel/bpf/syscall.c:6146
__do_sys_bpf kernel/bpf/syscall.c:6274 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6272 [inline]
__arm64_sys_bpf+0x24/0x34 kernel/bpf/syscall.c:6272
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x48/0x110 arch/arm64/kernel/syscall.c:49
el0_svc_common.constprop.0+0x40/0xe0 arch/arm64/kernel/syscall.c:132
do_el0_svc+0x1c/0x28 arch/arm64/kernel/syscall.c:151
el0_svc+0x34/0x128 arch/arm64/kernel/entry-common.c:724
el0t_64_sync_handler+0xa0/0xe4 arch/arm64/kernel/entry-common.c:743
el0t_64_sync+0x1a4/0x1a8 arch/arm64/kernel/entry.S:596

Freed by task 983:
kasan_save_stack+0x3c/0x64 mm/kasan/common.c:56
save_stack_info+0x40/0x158 mm/kasan/tags.c:106
__kasan_save_free_info+0x18/0x24 mm/kasan/tags.c:147
kasan_save_free_info mm/kasan/kasan.h:406 [inline]
poison_slab_object mm/kasan/common.c:252 [inline]
__kasan_slab_free+0x80/0x84 mm/kasan/common.c:284
kasan_slab_free include/linux/kasan.h:234 [inline]
kfree_nolock+0xcc/0x1d4 mm/slub.c:6929
range_tree_destroy+0x74/0x90 kernel/bpf/range_tree.c:253
arena_map_free+0x64/0x90 kernel/bpf/arena.c:196
bpf_map_free kernel/bpf/syscall.c:894 [inline]
bpf_map_free_deferred+0x70/0x180 kernel/bpf/syscall.c:921
process_one_work+0x178/0x2cc kernel/workqueue.c:3257
process_scheduled_works kernel/workqueue.c:3340 [inline]
worker_thread+0x24c/0x354 kernel/workqueue.c:3421
kthread+0x130/0x1fc kernel/kthread.c:463
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860

The buggy address belongs to the object at fff000000854f000
which belongs to the cache kmalloc-64 of size 64
The buggy address is located 32 bytes inside of
64-byte region [fff000000854f000, fff000000854f040)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xfbf000000854f200 pfn:0x4854f
flags: 0x1ffc00000000000(node=0|zone=0|lastcpupid=0x7ff|kasantag=0x0)
page_type: f5(slab)
raw: 01ffc00000000000 f9f0000003001600 dead000000000100 dead000000000122
raw: fbf000000854f200 000000008040003f 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
fff000000854ee00: f6 f6 f7 f7 fa fa f9 f9 f5 f5 fb fb f6 f6 fc fc
fff000000854ef00: f8 f8 f6 f6 f0 f0 f2 f2 f9 f9 f2 f2 f0 f0 fb fb
>fff000000854f000: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
^
fff000000854f100: fa fa fa fe fe fe fe fe fe fe fe fe fe fe fe fe
fff000000854f200: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
==================================================================


---
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***

Subject: [PATCH] mm/slub: reset KASAN tag in defer_free() before accessing freed memory
Author: karti...@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

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()")
Closes: https://syzkaller.appspot.com/bug?extid=7a25305a76d872abcfa1
Reported-by: syzbot+7a2530...@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---
mm/slub.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index e6a330e24145..46959c6da2cf 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -6534,6 +6534,8 @@ static void defer_free(struct kmem_cache *s, void *head)

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);
--
2.43.0

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+7a2530...@syzkaller.appspotmail.com
Tested-by: syzbot+7a2530...@syzkaller.appspotmail.com

Tested on:

commit: c9b47175 Merge tag 'i2c-for-6.19-rc1' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1055a1c2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c4d202b1d12ef31

dashboard link: https://syzkaller.appspot.com/bug?extid=7a25305a76d872abcfa1
compiler: aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

patch: https://syzkaller.appspot.com/x/patch.diff?x=129c6a1a580000

Note: testing is done by a robot and is best-effort only.