Re: KASAN: slab-out-of-bounds Write in record_print_text

[John Ogness]

On 2021-01-25, syzbot <syzbot+a42d84593d6a89a76f26@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> syzbot found the following issue on:
>
> HEAD commit:    e6806137 Merge tag 'irq_urgent_for_v5.11_rc5' of git://git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10c59c6f500000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=be33d8015c9de024
> dashboard link: https://syzkaller.appspot.com/bug?extid=a42d84593d6a89a76f26
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1575e6b4d00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17aea4e8d00000
>
> The issue was bisected to:
>
> commit f0e386ee0c0b71ea6f7238506a4d0965a2dbef11
> Author: John Ogness <john.ogness@xxxxxxxxxxxxx>
> Date:   Thu Jan 14 17:04:12 2021 +0000
>
>     printk: fix buffer overflow potential for print_text()

Thank you syzbot for your valuable work. A fix has already been posted
and queued:

https://lkml.kernel.org/r/20210124202728.4718-1-john.ogness@xxxxxxxxxxxxx

> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17f30130d00000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=140b0130d00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=100b0130d00000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a42d84593d6a89a76f26@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: f0e386ee0c0b ("printk: fix buffer overflow potential for print_text()")
>
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in record_print_text+0x33f/0x380 kernel/printk/printk.c:1401
> Write of size 1 at addr ffff88801c2faf40 by task in:imklog/8158
>
> CPU: 1 PID: 8158 Comm: in:imklog Not tainted 5.11.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x107/0x163 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:230
>  __kasan_report mm/kasan/report.c:396 [inline]
>  kasan_report.cold+0x79/0xd5 mm/kasan/report.c:413
>  record_print_text+0x33f/0x380 kernel/printk/printk.c:1401
>  syslog_print+0x2bb/0x430 kernel/printk/printk.c:1459
>  do_syslog.part.0+0x2a8/0x7c0 kernel/printk/printk.c:1586
>  do_syslog+0x49/0x60 kernel/printk/printk.c:1567
>  kmsg_read+0x90/0xb0 fs/proc/kmsg.c:40
>  pde_read fs/proc/inode.c:321 [inline]
>  proc_reg_read+0x119/0x300 fs/proc/inode.c:331
>  vfs_read+0x1b5/0x570 fs/read_write.c:494
>  ksys_read+0x12d/0x250 fs/read_write.c:634
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7f3e2eec922d
> Code: c1 20 00 00 75 10 b8 00 00 00 00 0f 05 48 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 4e fc ff ff 48 89 04 24 b8 00 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 97 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
> RSP: 002b:00007f3e2c865580 EFLAGS: 00000293 ORIG_RAX: 0000000000000000
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3e2eec922d
> RDX: 0000000000001fa0 RSI: 00007f3e2c865da0 RDI: 0000000000000004
> RBP: 000055d0880849d0 R08: 0000000000000000 R09: 0000000004000001
> R10: 0000000000000001 R11: 0000000000000293 R12: 00007f3e2c865da0
> R13: 0000000000001fa0 R14: 0000000000001f9f R15: 00007f3e2c865df3
>
> Allocated by task 8158:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_set_track mm/kasan/common.c:46 [inline]
>  set_alloc_info mm/kasan/common.c:401 [inline]
>  ____kasan_kmalloc.constprop.0+0x82/0xa0 mm/kasan/common.c:429
>  kmalloc include/linux/slab.h:552 [inline]
>  syslog_print+0xb2/0x430 kernel/printk/printk.c:1430
>  do_syslog.part.0+0x2a8/0x7c0 kernel/printk/printk.c:1586
>  do_syslog+0x49/0x60 kernel/printk/printk.c:1567
>  kmsg_read+0x90/0xb0 fs/proc/kmsg.c:40
>  pde_read fs/proc/inode.c:321 [inline]
>  proc_reg_read+0x119/0x300 fs/proc/inode.c:331
>  vfs_read+0x1b5/0x570 fs/read_write.c:494
>  ksys_read+0x12d/0x250 fs/read_write.c:634
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> The buggy address belongs to the object at ffff88801c2fa800
>  which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 832 bytes to the right of
>  1024-byte region [ffff88801c2fa800, ffff88801c2fac00)
> The buggy address belongs to the page:
> page:00000000eb65f4f5 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1c2f8
> head:00000000eb65f4f5 order:2 compound_mapcount:0 compound_pincount:0
> flags: 0xfff00000010200(slab|head)
> raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888010041140
> raw: 0000000000000000 0000000080080008 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff88801c2fae00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff88801c2fae80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>ffff88801c2faf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>                                            ^
>  ffff88801c2faf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff88801c2fb000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
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> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
>
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches