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    SubjectRe: KASAN: use-after-free Read in vc_do_resize
    From
    syzbot has found a reproducer for the following issue on:

    HEAD commit: bcf87687 Linux 5.8
    git tree: upstream
    console output: https://syzkaller.appspot.com/x/log.txt?x=1268f642900000
    kernel config: https://syzkaller.appspot.com/x/.config?x=19b11af1e394136d
    dashboard link: https://syzkaller.appspot.com/bug?extid=3c9716daab4ea34d814f
    compiler: gcc (GCC) 10.1.0-syz 20200507
    syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16f48ecc900000
    C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15dd8c78900000

    IMPORTANT: if you fix the issue, please add the following tag to the commit:
    Reported-by: syzbot+3c9716daab4ea34d814f@syzkaller.appspotmail.com

    ==================================================================
    BUG: KASAN: use-after-free in memcpy include/linux/string.h:406 [inline]
    BUG: KASAN: use-after-free in scr_memcpyw include/linux/vt_buffer.h:49 [inline]
    BUG: KASAN: use-after-free in vc_do_resize+0x9d6/0x13f0 drivers/tty/vt/vt.c:1286
    Read of size 2 at addr ffff88809da9f8c2 by task syz-executor887/23625

    CPU: 1 PID: 23625 Comm: syz-executor887 Not tainted 5.8.0-syzkaller #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    Call Trace:
    __dump_stack lib/dump_stack.c:77 [inline]
    dump_stack+0x18f/0x20d lib/dump_stack.c:118
    print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
    __kasan_report mm/kasan/report.c:513 [inline]
    kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
    check_memory_region_inline mm/kasan/generic.c:186 [inline]
    check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
    memcpy+0x20/0x60 mm/kasan/common.c:105
    memcpy include/linux/string.h:406 [inline]
    scr_memcpyw include/linux/vt_buffer.h:49 [inline]
    vc_do_resize+0x9d6/0x13f0 drivers/tty/vt/vt.c:1286
    fbcon_modechanged+0x36c/0x710 drivers/video/fbdev/core/fbcon.c:2990
    fbcon_update_vcs+0x3a/0x50 drivers/video/fbdev/core/fbcon.c:3048
    fb_set_var+0xae8/0xd60 drivers/video/fbdev/core/fbmem.c:1056
    do_fb_ioctl+0x33f/0x6c0 drivers/video/fbdev/core/fbmem.c:1109
    fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1185
    vfs_ioctl fs/ioctl.c:48 [inline]
    ksys_ioctl+0x11a/0x180 fs/ioctl.c:753
    __do_sys_ioctl fs/ioctl.c:762 [inline]
    __se_sys_ioctl fs/ioctl.c:760 [inline]
    __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:760
    do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
    entry_SYSCALL_64_after_hwframe+0x44/0xa9
    RIP: 0033:0x44aa19
    Code: e8 3c e6 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 2b 06 fc ff c3 66 2e 0f 1f 84 00 00 00 00
    RSP: 002b:00007f027d75bdb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
    RAX: ffffffffffffffda RBX: 00000000006e69f8 RCX: 000000000044aa19
    RDX: 0000000020000000 RSI: 0000000000004601 RDI: 0000000000000003
    RBP: 00000000006e69f0 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e69fc
    R13: 00007ffcf24f523f R14: 00007f027d75c9c0 R15: 20c49ba5e353f7cf

    Allocated by task 23115:
    save_stack+0x1b/0x40 mm/kasan/common.c:48
    set_track mm/kasan/common.c:56 [inline]
    __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
    kmem_cache_alloc_trace+0x14f/0x2d0 mm/slab.c:3551
    kmalloc include/linux/slab.h:555 [inline]
    kzalloc include/linux/slab.h:669 [inline]
    apparmor_sk_alloc_security+0x79/0xf0 security/apparmor/lsm.c:776
    security_sk_alloc+0x50/0xb0 security/security.c:2180
    sk_prot_alloc+0xae/0x300 net/core/sock.c:1696
    sk_alloc+0x32/0xbd0 net/core/sock.c:1747
    unix_create1+0xbf/0x730 net/unix/af_unix.c:795
    unix_create+0xf9/0x1e0 net/unix/af_unix.c:857
    __sock_create+0x3ca/0x740 net/socket.c:1428
    sock_create net/socket.c:1479 [inline]
    __sys_socketpair+0x242/0x570 net/socket.c:1583
    __do_sys_socketpair net/socket.c:1632 [inline]
    __se_sys_socketpair net/socket.c:1629 [inline]
    __x64_sys_socketpair+0x93/0xf0 net/socket.c:1629
    do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

    Freed by task 23107:
    save_stack+0x1b/0x40 mm/kasan/common.c:48
    set_track mm/kasan/common.c:56 [inline]
    kasan_set_free_info mm/kasan/common.c:316 [inline]
    __kasan_slab_free+0xf5/0x140 mm/kasan/common.c:455
    __cache_free mm/slab.c:3426 [inline]
    kfree+0x103/0x2c0 mm/slab.c:3757
    security_sk_free+0x3e/0x70 security/security.c:2185
    sk_prot_free net/core/sock.c:1726 [inline]
    __sk_destruct+0x537/0x860 net/core/sock.c:1815
    sk_destruct+0xbd/0xe0 net/core/sock.c:1830
    __sk_free+0xef/0x3d0 net/core/sock.c:1841
    sk_free+0x78/0xa0 net/core/sock.c:1852
    sock_put include/net/sock.h:1781 [inline]
    unix_release_sock+0x7fc/0xc10 net/unix/af_unix.c:574
    unix_release+0x3f/0x80 net/unix/af_unix.c:867
    __sock_release+0xcd/0x280 net/socket.c:605
    sock_close+0x18/0x20 net/socket.c:1278
    __fput+0x33c/0x880 fs/file_table.c:281
    task_work_run+0xdd/0x190 kernel/task_work.c:135
    tracehook_notify_resume include/linux/tracehook.h:188 [inline]
    exit_to_usermode_loop arch/x86/entry/common.c:239 [inline]
    __prepare_exit_to_usermode+0x1e9/0x1f0 arch/x86/entry/common.c:269
    do_syscall_64+0x6c/0xe0 arch/x86/entry/common.c:393
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

    The buggy address belongs to the object at ffff88809da9f8c0
    which belongs to the cache kmalloc-32 of size 32
    The buggy address is located 2 bytes inside of
    32-byte region [ffff88809da9f8c0, ffff88809da9f8e0)
    The buggy address belongs to the page:
    page:ffffea000276a7c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88809da9ffc1
    flags: 0xfffe0000000200(slab)
    raw: 00fffe0000000200 ffffea0002789fc8 ffffea0002a46148 ffff8880aa0001c0
    raw: ffff88809da9ffc1 ffff88809da9f000 000000010000003c 0000000000000000
    page dumped because: kasan: bad access detected

    Memory state around the buggy address:
    ffff88809da9f780: 00 00 00 fc fc fc fc fc fb fb fb fb fc fc fc fc
    ffff88809da9f800: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
    >ffff88809da9f880: 00 02 fc fc fc fc fc fc fb fb fb fb fc fc fc fc
    ^
    ffff88809da9f900: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
    ffff88809da9f980: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
    ==================================================================

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