linux-kernel - Re: [syzbot] [kernel?] KMSAN: kernel-infoleak-after-free in copy_siginfo_to

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Date: Mon, 25 Dec 2023 14:15:18 -0800
From: syzbot <syzbot+cfc08744435c4cf94a40@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, luto@...nel.org, peterz@...radead.org, 
	syzkaller-bugs@...glegroups.com, tglx@...utronix.de, xrivendell7@...il.com
Subject: Re: [syzbot] [kernel?] KMSAN: kernel-infoleak-after-free in
 copy_siginfo_to_user (2)

syzbot has found a reproducer for the following issue on:

HEAD commit:    861deac3b092 Linux 6.7-rc7
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=15826ec9e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e0c7078a6b901aa3
dashboard link: https://syzkaller.appspot.com/bug?extid=cfc08744435c4cf94a40
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17ea5231e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0ea60ee8ed32/disk-861deac3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6d69fdc33021/vmlinux-861deac3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f0158750d452/bzImage-861deac3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+cfc08744435c4cf94a40@...kaller.appspotmail.com

=====================================================
BUG: KMSAN: kernel-infoleak-after-free in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
BUG: KMSAN: kernel-infoleak-after-free in _copy_to_user+0xbc/0x100 lib/usercopy.c:40
 instrument_copy_to_user include/linux/instrumented.h:114 [inline]
 _copy_to_user+0xbc/0x100 lib/usercopy.c:40
 copy_to_user include/linux/uaccess.h:191 [inline]
 copy_siginfo_to_user+0x40/0x130 kernel/signal.c:3374
 ptrace_request+0xfa6/0x36d0 kernel/ptrace.c:1066
 arch_ptrace+0x435/0x680 arch/x86/kernel/ptrace.c:848
 __do_sys_ptrace kernel/ptrace.c:1305 [inline]
 __se_sys_ptrace+0x2d8/0x750 kernel/ptrace.c:1278
 __x64_sys_ptrace+0xbd/0x110 kernel/ptrace.c:1278
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

Uninit was stored to memory at:
 copy_siginfo include/linux/signal.h:17 [inline]
 ptrace_getsiginfo kernel/ptrace.c:705 [inline]
 ptrace_request+0xf32/0x36d0 kernel/ptrace.c:1064
 arch_ptrace+0x435/0x680 arch/x86/kernel/ptrace.c:848
 __do_sys_ptrace kernel/ptrace.c:1305 [inline]
 __se_sys_ptrace+0x2d8/0x750 kernel/ptrace.c:1278
 __x64_sys_ptrace+0xbd/0x110 kernel/ptrace.c:1278
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

Uninit was stored to memory at:
 copy_siginfo include/linux/signal.h:17 [inline]
 collect_signal kernel/signal.c:596 [inline]
 __dequeue_signal+0x548/0xa00 kernel/signal.c:625
 dequeue_signal+0x14b/0xb10 kernel/signal.c:648
 get_signal+0xc3f/0x2d10 kernel/signal.c:2784
 arch_do_signal_or_restart+0x53/0xca0 arch/x86/kernel/signal.c:309
 exit_to_user_mode_loop+0xe8/0x320 kernel/entry/common.c:168
 exit_to_user_mode_prepare+0x163/0x220 kernel/entry/common.c:204
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x2a/0x140 kernel/entry/common.c:296
 do_syscall_64+0x50/0x110 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

Uninit was created at:
 slab_free_hook mm/slub.c:1770 [inline]
 slab_free_freelist_hook mm/slub.c:1826 [inline]
 slab_free mm/slub.c:3809 [inline]
 kmem_cache_free+0x66f/0x1250 mm/slub.c:3831
 __sigqueue_free kernel/signal.c:460 [inline]
 collect_signal kernel/signal.c:603 [inline]
 __dequeue_signal+0x998/0xa00 kernel/signal.c:625
 dequeue_signal+0x14b/0xb10 kernel/signal.c:648
 get_signal+0xc3f/0x2d10 kernel/signal.c:2784
 arch_do_signal_or_restart+0x53/0xca0 arch/x86/kernel/signal.c:309
 exit_to_user_mode_loop+0xe8/0x320 kernel/entry/common.c:168
 exit_to_user_mode_prepare+0x163/0x220 kernel/entry/common.c:204
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x2a/0x140 kernel/entry/common.c:296
 do_syscall_64+0x50/0x110 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

Bytes 12-15 of 48 are uninitialized
Memory access of size 48 starts at ffff888115d6bc80
Data copied to user address 00000000016164e0

CPU: 1 PID: 5004 Comm: strace-static-x Not tainted 6.7.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
=====================================================


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.