Re: KMSAN: kernel-infoleak in copy_siginfo_to_user (2)

[Eric W. Biederman]

Andrew,

Didn't someone already provide a fix for this one?

I thought  I saw that hit your tree a while ago.  I am looking in
ptrace.c and I don't see anything that would have fixed this issue.

If there isn't a fix in the queue I will take a stab at it.

Thank you
Eric

syzbot <syzbot+0d602a1b0d8c95bdf299@xxxxxxxxxxxxxxxxxxxxxxxxx> writes:

> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    d062d017 usb-fuzzer: main usb gadget fuzzer driver
> git tree:       kmsan
> console output: https://syzkaller.appspot.com/x/log.txt?x=137348b4a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=67ebf8b3cce62ce7
> dashboard link: https://syzkaller.appspot.com/bug?extid=0d602a1b0d8c95bdf299
> compiler:       clang version 9.0.0 (/home/glider/llvm/clang
> 06d00afa61eef8f7f501ebdb4e8612ea43ec2d78)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=175d65e0a00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14ae05c0a00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+0d602a1b0d8c95bdf299@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ptrace attach of "./syz-executor353086472"[10278] was attempted by
> "./syz-executor353086472"[10279]
> ptrace attach of "./syz-executor353086472"[10280] was attempted by
> "./syz-executor353086472"[10281]
> ptrace attach of "./syz-executor353086472"[10282] was attempted by
> "./syz-executor353086472"[10283]
> ==================================================================
> BUG: KMSAN: kernel-infoleak in _copy_to_user+0x16b/0x1f0 lib/usercopy.c:32
> CPU: 1 PID: 10284 Comm: syz-executor353 Not tainted 5.1.0-rc7+ #5
> 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+0x191/0x1f0 lib/dump_stack.c:113
>  kmsan_report+0x130/0x2a0 mm/kmsan/kmsan.c:619
>  kmsan_internal_check_memory+0x974/0xa80 mm/kmsan/kmsan.c:713
>  kmsan_copy_to_user+0xa9/0xb0 mm/kmsan/kmsan_hooks.c:492
>  _copy_to_user+0x16b/0x1f0 lib/usercopy.c:32
>  copy_to_user include/linux/uaccess.h:174 [inline]
>  copy_siginfo_to_user+0x80/0x160 kernel/signal.c:3059
>  ptrace_peek_siginfo kernel/ptrace.c:742 [inline]
>  ptrace_request+0x24bd/0x2950 kernel/ptrace.c:913
>  arch_ptrace+0x9fa/0x1090 arch/x86/kernel/ptrace.c:868
>  __do_sys_ptrace kernel/ptrace.c:1155 [inline]
>  __se_sys_ptrace+0x2b9/0x7b0 kernel/ptrace.c:1120
>  __x64_sys_ptrace+0x56/0x70 kernel/ptrace.c:1120
>  do_syscall_64+0xbc/0xf0 arch/x86/entry/common.c:291
>  entry_SYSCALL_64_after_hwframe+0x63/0xe7
> RIP: 0033:0x441cc9
> Code: e8 bc 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 1b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00000000007efdd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000065
> RAX: ffffffffffffffda RBX: 0000000000000063 RCX: 0000000000441cc9
> RDX: 00000000200000c0 RSI: 0000000000000007 RDI: 0000000000004209
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000716000 R11: 0000000000000246 R12: 0000000000000002
> R13: 0000000000402a00 R14: 0000000000000000 R15: 0000000000000000
>
> Local variable description: ----info.i@ptrace_request
> Variable was created at:
>  ptrace_peek_siginfo kernel/ptrace.c:714 [inline]
>  ptrace_request+0x2161/0x2950 kernel/ptrace.c:913
>  arch_ptrace+0x9fa/0x1090 arch/x86/kernel/ptrace.c:868
>
> Bytes 0-47 of 48 are uninitialized
> Memory access of size 48 starts at ffff8880a902fd70
> Data copied to user address 0000000000716000
> ==================================================================
>
>
> ---
> 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@xxxxxxxxxxxxxxxxx
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches