KASAN: use-after-free Read in copy_folio_from_iter

Kernel	Title	Rank 🛈	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
upstream	KASAN: use-after-free Read in copy_folio_from_iter_atomic jfs	19				3	134d	196d	0/29	auto-obsoleted due to no activity on 2025/11/17 22:24
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BUG: KASAN: use-after-free in memcpy_from_iter lib/iov_iter.c:85 [inline]
BUG: KASAN: use-after-free in iterate_bvec include/linux/iov_iter.h:123 [inline]
BUG: KASAN: use-after-free in iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
BUG: KASAN: use-after-free in iterate_and_advance include/linux/iov_iter.h:330 [inline]
BUG: KASAN: use-after-free in __copy_from_iter lib/iov_iter.c:261 [inline]
BUG: KASAN: use-after-free in copy_folio_from_iter_atomic+0xb7c/0x164c lib/iov_iter.c:491
Read of size 4096 at addr ffff0000d64c3000 by task kworker/u8:7/642

CPU: 0 UID: 0 PID: 642 Comm: kworker/u8:7 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
Workqueue: loop2 loop_workfn
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 print_address_description+0xa8/0x238 mm/kasan/report.c:378
 print_report+0x68/0x84 mm/kasan/report.c:482
 kasan_report+0xb0/0x110 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2a4 mm/kasan/generic.c:200
 __asan_memcpy+0x3c/0x84 mm/kasan/shadow.c:105
 memcpy_from_iter lib/iov_iter.c:85 [inline]
 iterate_bvec include/linux/iov_iter.h:123 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 __copy_from_iter lib/iov_iter.c:261 [inline]
 copy_folio_from_iter_atomic+0xb7c/0x164c lib/iov_iter.c:491
 generic_perform_write+0x4d0/0x7bc mm/filemap.c:4332
 shmem_file_write_iter+0x10c/0x134 mm/shmem.c:3490
 lo_rw_aio+0x8f4/0xa78 drivers/block/loop.c:-1
 do_req_filebacked drivers/block/loop.c:-1 [inline]
 loop_handle_cmd drivers/block/loop.c:1926 [inline]
 loop_process_work+0x808/0x1058 drivers/block/loop.c:1961
 loop_workfn+0x50/0x64 drivers/block/loop.c:1985
 process_one_work+0x7c0/0x1558 kernel/workqueue.c:3257
 process_scheduled_works kernel/workqueue.c:3340 [inline]
 worker_thread+0x958/0xed8 kernel/workqueue.c:3421
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x25 pfn:0x1164c3
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000000000 fffffdffc3658c48 fffffdffc353db88 0000000000000000
raw: 0000000000000025 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000d64c2f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff0000d64c2f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff0000d64c3000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff0000d64c3080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000d64c3100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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