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Date: Thu, 19 Jul 2018 17:07:18 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: syzbot <syzbot+b173e77096a8ba815511@...kaller.appspotmail.com>
Cc: jack@...e.cz, jlayton@...hat.com, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, mgorman@...hsingularity.net,
syzkaller-bugs@...glegroups.com, willy@...radead.org,
v9fs-developer@...ts.sourceforge.net
Subject: Re: KASAN: use-after-free Read in generic_perform_write
On Thu, 19 Jul 2018 11:01:01 -0700 syzbot <syzbot+b173e77096a8ba815511@...kaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 1c34981993da Add linux-next specific files for 20180719
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=16e6ac44400000
> kernel config: https://syzkaller.appspot.com/x/.config?x=7002497517b09aec
> dashboard link: https://syzkaller.appspot.com/bug?extid=b173e77096a8ba815511
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
Thanks. I cc'ed v9fs-developer, optimistically. That list manager is
weird :(
I'm suspecting v9fs. Does that fs attempt to write to the fs from a
kmalloced buffer?
Full report below...
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+b173e77096a8ba815511@...kaller.appspotmail.com
>
> IPVS: length: 141 != 24
> XFS (loop5): Invalid superblock magic number
> ==================================================================
> BUG: KASAN: use-after-free in memcpy include/linux/string.h:345 [inline]
> BUG: KASAN: use-after-free in iov_iter_copy_from_user_atomic+0xb8d/0xfa0
> lib/iov_iter.c:916
> Read of size 21 at addr ffff880190103660 by task kworker/0:3/4927
>
> CPU: 0 PID: 4927 Comm: kworker/0:3 Not tainted 4.18.0-rc5-next-20180719+ #11
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: events p9_write_work
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
> print_address_description+0x6c/0x20b mm/kasan/report.c:256
> kasan_report_error mm/kasan/report.c:354 [inline]
> kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
> check_memory_region_inline mm/kasan/kasan.c:260 [inline]
> check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
> memcpy+0x23/0x50 mm/kasan/kasan.c:302
> memcpy include/linux/string.h:345 [inline]
> iov_iter_copy_from_user_atomic+0xb8d/0xfa0 lib/iov_iter.c:916
> generic_perform_write+0x469/0x6c0 mm/filemap.c:3058
> __generic_file_write_iter+0x26e/0x630 mm/filemap.c:3175
> ext4_file_write_iter+0x390/0x1450 fs/ext4/file.c:266
> call_write_iter include/linux/fs.h:1826 [inline]
> new_sync_write fs/read_write.c:474 [inline]
> __vfs_write+0x6af/0x9d0 fs/read_write.c:487
> vfs_write+0x1fc/0x560 fs/read_write.c:549
> kernel_write+0xab/0x120 fs/read_write.c:526
> p9_fd_write net/9p/trans_fd.c:427 [inline]
> p9_write_work+0x6f1/0xd50 net/9p/trans_fd.c:476
> process_one_work+0xc73/0x1ba0 kernel/workqueue.c:2153
> worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
> kthread+0x345/0x410 kernel/kthread.c:246
> ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415
>
> Allocated by task 13072:
> save_stack+0x43/0xd0 mm/kasan/kasan.c:448
> set_track mm/kasan/kasan.c:460 [inline]
> kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
> __do_kmalloc mm/slab.c:3718 [inline]
> __kmalloc+0x14e/0x760 mm/slab.c:3727
> kmalloc include/linux/slab.h:518 [inline]
> p9_fcall_alloc+0x1e/0x90 net/9p/client.c:237
> p9_tag_alloc net/9p/client.c:266 [inline]
> p9_client_prepare_req.part.8+0x107/0xa00 net/9p/client.c:640
> p9_client_prepare_req net/9p/client.c:675 [inline]
> p9_client_rpc+0x242/0x1330 net/9p/client.c:675
> p9_client_version net/9p/client.c:890 [inline]
> p9_client_create+0xca4/0x1537 net/9p/client.c:974
> v9fs_session_init+0x21a/0x1a80 fs/9p/v9fs.c:400
> v9fs_mount+0x7c/0x900 fs/9p/vfs_super.c:135
> legacy_get_tree+0x131/0x460 fs/fs_context.c:674
> vfs_get_tree+0x1cb/0x5c0 fs/super.c:1743
> do_new_mount fs/namespace.c:2603 [inline]
> do_mount+0x6f2/0x1e20 fs/namespace.c:2927
> ksys_mount+0x12d/0x140 fs/namespace.c:3143
> __do_sys_mount fs/namespace.c:3157 [inline]
> __se_sys_mount fs/namespace.c:3154 [inline]
> __x64_sys_mount+0xbe/0x150 fs/namespace.c:3154
> do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 13072:
> save_stack+0x43/0xd0 mm/kasan/kasan.c:448
> set_track mm/kasan/kasan.c:460 [inline]
> __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
> kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
> __cache_free mm/slab.c:3498 [inline]
> kfree+0xd9/0x260 mm/slab.c:3813
> p9_free_req+0xb5/0x120 net/9p/client.c:338
> p9_client_rpc+0xa8e/0x1330 net/9p/client.c:739
> p9_client_version net/9p/client.c:890 [inline]
> p9_client_create+0xca4/0x1537 net/9p/client.c:974
> v9fs_session_init+0x21a/0x1a80 fs/9p/v9fs.c:400
> v9fs_mount+0x7c/0x900 fs/9p/vfs_super.c:135
> legacy_get_tree+0x131/0x460 fs/fs_context.c:674
> vfs_get_tree+0x1cb/0x5c0 fs/super.c:1743
> do_new_mount fs/namespace.c:2603 [inline]
> do_mount+0x6f2/0x1e20 fs/namespace.c:2927
> ksys_mount+0x12d/0x140 fs/namespace.c:3143
> __do_sys_mount fs/namespace.c:3157 [inline]
> __se_sys_mount fs/namespace.c:3154 [inline]
> __x64_sys_mount+0xbe/0x150 fs/namespace.c:3154
> do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff880190103640
> which belongs to the cache kmalloc-16384 of size 16384
> The buggy address is located 32 bytes inside of
> 16384-byte region [ffff880190103640, ffff880190107640)
> The buggy address belongs to the page:
> page:ffffea0006404000 count:1 mapcount:0 mapping:ffff8801da802200 index:0x0
> compound_mapcount: 0
> flags: 0x2fffc0000010200(slab|head)
> raw: 02fffc0000010200 ffffea000643b808 ffffea0006452c08 ffff8801da802200
> raw: 0000000000000000 ffff880190103640 0000000100000001 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff880190103500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff880190103580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > ffff880190103600: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> ^
> ffff880190103680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff880190103700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
>
> ---
> This bug 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 bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
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