Re: [syzbot] [kernel?] KMSAN: kernel-infoleak-after-free in copy_siginfo_to_user (2)

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    70293240c5ce Merge tag 'timers-urgent-2024-03-23' of git:/..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=139071be180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e6bd769cb793b98a
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=14694231180000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15846fc1180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0de52742d0b8/disk-70293240.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f304697881bf/vmlinux-70293240.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2b9d8a9376f0/bzImage-70293240.xz

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

=====================================================
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/0x110 lib/usercopy.c:40
 instrument_copy_to_user include/linux/instrumented.h:114 [inline]
 _copy_to_user+0xbc/0x110 lib/usercopy.c:40
 copy_to_user include/linux/uaccess.h:191 [inline]
 copy_siginfo_to_user+0x40/0x130 kernel/signal.c:3380
 ptrace_request+0xfa7/0x36e0 kernel/ptrace.c:1046
 arch_ptrace+0x43b/0x680 arch/x86/kernel/ptrace.c:848
 __do_sys_ptrace kernel/ptrace.c:1285 [inline]
 __se_sys_ptrace+0x2d8/0x760 kernel/ptrace.c:1258
 __x64_sys_ptrace+0xbd/0x110 kernel/ptrace.c:1258
 do_syscall_64+0xd5/0x1f0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was stored to memory at:
 copy_siginfo include/linux/signal.h:18 [inline]
 ptrace_getsiginfo kernel/ptrace.c:685 [inline]
 ptrace_request+0xf33/0x36e0 kernel/ptrace.c:1044
 arch_ptrace+0x43b/0x680 arch/x86/kernel/ptrace.c:848
 __do_sys_ptrace kernel/ptrace.c:1285 [inline]
 __se_sys_ptrace+0x2d8/0x760 kernel/ptrace.c:1258
 __x64_sys_ptrace+0xbd/0x110 kernel/ptrace.c:1258
 do_syscall_64+0xd5/0x1f0
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was stored to memory at:
 copy_siginfo include/linux/signal.h:18 [inline]
 collect_signal kernel/signal.c:587 [inline]
 __dequeue_signal+0x501/0xad0 kernel/signal.c:616
 dequeue_signal+0x14b/0xb20 kernel/signal.c:639
 get_signal+0xb46/0x2d00 kernel/signal.c:2790
 arch_do_signal_or_restart+0x53/0xcb0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x5d/0x160 kernel/entry/common.c:218
 do_syscall_64+0xe4/0x1f0 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was created at:
 slab_free_hook mm/slub.c:2073 [inline]
 slab_free mm/slub.c:4280 [inline]
 kmem_cache_free+0x257/0xa80 mm/slub.c:4344
 __sigqueue_free kernel/signal.c:451 [inline]
 collect_signal kernel/signal.c:594 [inline]
 __dequeue_signal+0xa58/0xad0 kernel/signal.c:616
 dequeue_signal+0x14b/0xb20 kernel/signal.c:639
 get_signal+0xb46/0x2d00 kernel/signal.c:2790
 arch_do_signal_or_restart+0x53/0xcb0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x5d/0x160 kernel/entry/common.c:218
 do_syscall_64+0xe4/0x1f0 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Bytes 12-15 of 48 are uninitialized
Memory access of size 48 starts at ffff8881240cfc60
Data copied to user address 0000000014dcf540

CPU: 1 PID: 5012 Comm: strace-static-x Not tainted 6.8.0-syzkaller-13213-g70293240c5ce #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
=====================================================


---
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.