Message-ID: <CACT4Y+aGfOE7R+LoocX7aW2XObY4aCAsAydwvL+Ni_NUt6JfJA@mail.gmail.com>
Date:   Tue, 2 May 2023 09:15:57 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+01e9a564dc6b3289cea3@...kaller.appspotmail.com>
Cc:     brauner@...nel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        alexghiti@...osinc.com, Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [syzbot] [fs?] KASAN: stack-out-of-bounds Read in proc_pid_stack

On Tue, 2 May 2023 at 09:05, syzbot
<syzbot+01e9a564dc6b3289cea3@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    950b879b7f02 riscv: Fixup race condition on PG_dcache_clea..
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes
> console output: https://syzkaller.appspot.com/x/log.txt?x=10c4c1f7c80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ecebece1b90c0342
> dashboard link: https://syzkaller.appspot.com/bug?extid=01e9a564dc6b3289cea3
> compiler:       riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> userspace arch: riscv64
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+01e9a564dc6b3289cea3@...kaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: stack-out-of-bounds in walk_stackframe+0x128/0x2fe arch/riscv/kernel/stacktrace.c:58
> Read of size 8 at addr ff200000030a79b0 by task syz-executor.1/7894
>
> CPU: 0 PID: 7894 Comm: syz-executor.1 Tainted: G        W          6.2.0-rc1-syzkaller #0
> Hardware name: riscv-virtio,qemu (DT)
> Call Trace:
> [<ffffffff8000b9ea>] dump_backtrace+0x2e/0x3c arch/riscv/kernel/stacktrace.c:121
> [<ffffffff83402b96>] show_stack+0x34/0x40 arch/riscv/kernel/stacktrace.c:127
> [<ffffffff83442726>] __dump_stack lib/dump_stack.c:88 [inline]
> [<ffffffff83442726>] dump_stack_lvl+0xe0/0x14c lib/dump_stack.c:106
> [<ffffffff83409674>] print_address_description mm/kasan/report.c:306 [inline]
> [<ffffffff83409674>] print_report+0x1e4/0x4c0 mm/kasan/report.c:417
> [<ffffffff804ead14>] kasan_report+0xb8/0xe6 mm/kasan/report.c:517
> [<ffffffff804ebea4>] check_region_inline mm/kasan/generic.c:183 [inline]
> [<ffffffff804ebea4>] __asan_load8+0x7e/0xa6 mm/kasan/generic.c:256
> [<ffffffff8000b782>] walk_stackframe+0x128/0x2fe arch/riscv/kernel/stacktrace.c:58

+riscv maintainers

I think this is an issue in riscv stack walking.
If it's imprecise or walks stacks of running tasks, it needs to use
READ_ONCE_NOCHECK.

#syz set subsystems: riscv


> [<ffffffff8000bc66>] arch_stack_walk+0x2c/0x3c arch/riscv/kernel/stacktrace.c:154
> [<ffffffff80190822>] stack_trace_save_tsk+0x14a/0x1bc kernel/stacktrace.c:150
> [<ffffffff80697822>] proc_pid_stack+0x146/0x1ee fs/proc/base.c:456
> [<ffffffff80698bb0>] proc_single_show+0x9c/0x148 fs/proc/base.c:777
> [<ffffffff805af580>] traverse.part.0+0x74/0x2ca fs/seq_file.c:111
> [<ffffffff805aff02>] traverse fs/seq_file.c:101 [inline]
> [<ffffffff805aff02>] seq_read_iter+0x72c/0x934 fs/seq_file.c:195
> [<ffffffff805b0224>] seq_read+0x11a/0x16e fs/seq_file.c:162
> [<ffffffff805453ea>] do_loop_readv_writev fs/read_write.c:756 [inline]
> [<ffffffff805453ea>] do_loop_readv_writev fs/read_write.c:743 [inline]
> [<ffffffff805453ea>] do_iter_read+0x324/0x3c2 fs/read_write.c:798
> [<ffffffff805455f8>] vfs_readv+0xfe/0x166 fs/read_write.c:916
> [<ffffffff80549c66>] do_preadv fs/read_write.c:1008 [inline]
> [<ffffffff80549c66>] __do_sys_preadv fs/read_write.c:1058 [inline]
> [<ffffffff80549c66>] sys_preadv+0x182/0x1fa fs/read_write.c:1053
> [<ffffffff80005ff6>] ret_from_syscall+0x0/0x2
>
> The buggy address belongs to the virtual mapping at
>  [ff200000030a0000, ff200000030a9000) created by:
>  kernel_clone+0xee/0x914 kernel/fork.c:2681
>
> The buggy address belongs to the physical page:
> page:ff1c0000024e5f00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x9397c
> memcg:ff6000000ffd7202
> flags: 0xffe000000000000(node=0|zone=0|lastcpupid=0x7ff)
> raw: 0ffe000000000000 0000000000000000 0000000000000122 0000000000000000
> raw: 0000000000000000 0000000000000000 00000001ffffffff ff6000000ffd7202
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x102dc2(GFP_HIGHUSER|__GFP_NOWARN|__GFP_ZERO), pid 7873, tgid 7873 (syz-executor.1), ts 4012100669800, free_ts 4010400733200
>  __set_page_owner+0x32/0x182 mm/page_owner.c:190
>  set_page_owner include/linux/page_owner.h:31 [inline]
>  post_alloc_hook+0xf8/0x11a mm/page_alloc.c:2524
>  prep_new_page mm/page_alloc.c:2531 [inline]
>  get_page_from_freelist+0xc0e/0x1118 mm/page_alloc.c:4283
>  __alloc_pages+0x1b0/0x165a mm/page_alloc.c:5549
>  alloc_pages+0x132/0x25e mm/mempolicy.c:2286
>  vm_area_alloc_pages mm/vmalloc.c:2989 [inline]
>  __vmalloc_area_node mm/vmalloc.c:3057 [inline]
>  __vmalloc_node_range+0x81c/0xdb4 mm/vmalloc.c:3227
>  alloc_thread_stack_node kernel/fork.c:311 [inline]
>  dup_task_struct kernel/fork.c:987 [inline]
>  copy_process+0x210e/0x4068 kernel/fork.c:2097
>  kernel_clone+0xee/0x914 kernel/fork.c:2681
>  __do_sys_clone+0xec/0x120 kernel/fork.c:2822
>  sys_clone+0x32/0x44 kernel/fork.c:2790
>  ret_from_syscall+0x0/0x2
> page last free stack trace:
>  __reset_page_owner+0x4a/0xf8 mm/page_owner.c:148
>  reset_page_owner include/linux/page_owner.h:24 [inline]
>  free_pages_prepare mm/page_alloc.c:1446 [inline]
>  free_pcp_prepare+0x254/0x48e mm/page_alloc.c:1496
>  free_unref_page_prepare mm/page_alloc.c:3369 [inline]
>  free_unref_page_list+0x11e/0x736 mm/page_alloc.c:3510
>  release_pages+0x85a/0xbb2 mm/swap.c:1076
>  free_pages_and_swap_cache+0x76/0x88 mm/swap_state.c:311
>  tlb_batch_pages_flush+0x86/0x10c mm/mmu_gather.c:97
>  tlb_flush_mmu_free mm/mmu_gather.c:292 [inline]
>  tlb_flush_mmu mm/mmu_gather.c:299 [inline]
>  tlb_finish_mmu+0xcc/0x280 mm/mmu_gather.c:391
>  exit_mmap+0x190/0x686 mm/mmap.c:3096
>  __mmput+0x98/0x290 kernel/fork.c:1207
>  mmput+0x74/0x88 kernel/fork.c:1229
>  exit_mm kernel/exit.c:563 [inline]
>  do_exit+0x602/0x17be kernel/exit.c:854
>  do_group_exit+0x8e/0x15e kernel/exit.c:1012
>  __do_sys_exit_group kernel/exit.c:1023 [inline]
>  __wake_up_parent+0x0/0x4a kernel/exit.c:1021
>  ret_from_syscall+0x0/0x2
>
> Memory state around the buggy address:
>  ff200000030a7880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ff200000030a7900: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 f2 f2
> >ff200000030a7980: 00 00 00 f3 f3 f3 f3 f3 00 00 00 00 00 00 00 00
>                                      ^
>  ff200000030a7a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ff200000030a7a80: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the bug is already fixed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want to change bug's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the bug is a duplicate of another bug, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup
>
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