On Mon, Sep 30, 2024 at 12:39:24AM GMT, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: e7ed34365879 Merge tag 'mailbox-v6.12' of git://git.kernel.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=15238ea9980000 > kernel config: https://syzkaller.appspot.com/x/.config?x=8bfe37bd3f5983d6 > dashboard link: https://syzkaller.appspot.com/bug?extid=d207c41e97001109b49d > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40 > > Unfortunately, I don't have any reproducer for this issue yet. > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/c86c1297298e/disk-e7ed3436.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/8313c0846b3b/vmlinux-e7ed3436.xz > kernel image: https://storage.googleapis.com/syzbot-assets/8af10d85db09/bzImage-e7ed3436.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+d207c41e97001109b49d@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KCSAN: data-race in exec_mmap / vms_clear_ptes > > write to 0xffff888102fbaae8 of 8 bytes by task 3004 on cpu 1: > update_hiwater_rss include/linux/mm.h:2655 [inline] OK so this sets mm_struct->hiwater_rss on munmap() via update_hiwater_rss() in vms_clear_ptes()... > vms_clear_ptes+0x1a7/0x300 mm/vma.c:1088 > vms_complete_munmap_vmas+0x170/0x480 mm/vma.c:1140 > do_vmi_align_munmap+0x349/0x390 mm/vma.c:1349 > do_vmi_munmap+0x1eb/0x230 mm/vma.c:1397 > __vm_munmap+0xfd/0x220 mm/mmap.c:1600 > __do_sys_munmap mm/mmap.c:1617 [inline] > __se_sys_munmap mm/mmap.c:1614 [inline] > __x64_sys_munmap+0x36/0x40 mm/mmap.c:1614 > x64_sys_call+0xd32/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:12 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > read to 0xffff888102fbaae8 of 8 bytes by task 5494 on cpu 0: > get_mm_hiwater_rss include/linux/mm.h:2642 [inline] ...And a racing execve() is trying to read it. This is a bit of a tricky race, as we downgrade the write lock to a read lock in vms_complete_munmap_vmas(), which allows exec_mmap() to proceed (as it's under a read lock), and update_hiwater_rss() is called against vms->vma->vm_mm which is set to the old_mm and... I wonder if we should just be referencing current->mm in vms_clear_ptes() which would avoid this as will be the new mm that has been execve'd in (and presumably do nothing)? I don't think in practice this should have too egregious an impact as the process is being execve()'d anyway, so I think we can wait for Liam to return from leave to give his input. On your return - Liam what do you think? :) > setmax_mm_hiwater_rss include/linux/mm.h:2672 [inline] > exec_mmap+0x2d0/0x440 fs/exec.c:1012 > begin_new_exec+0xaf9/0x10b0 fs/exec.c:1280 > load_elf_binary+0x63b/0x19e0 fs/binfmt_elf.c:996 > search_binary_handler fs/exec.c:1752 [inline] > exec_binprm fs/exec.c:1794 [inline] > bprm_execve+0x4e6/0xc30 fs/exec.c:1845 > do_execveat_common+0x793/0x800 fs/exec.c:1952 > do_execve fs/exec.c:2026 [inline] > __do_sys_execve fs/exec.c:2102 [inline] > __se_sys_execve fs/exec.c:2097 [inline] > __x64_sys_execve+0x5a/0x70 fs/exec.c:2097 > x64_sys_call+0x1277/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:60 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > value changed: 0x000000000000022b -> 0x000000000000024b > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 UID: 0 PID: 5494 Comm: dhcpcd Not tainted 6.11.0-syzkaller-12113-ge7ed34365879 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 > ================================================================== > > > --- > This report 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@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > If the report is already addressed, let syzbot know by replying with: > #syz fix: exact-commit-title > > If you want to overwrite report's subsystems, reply with: > #syz set subsystems: new-subsystem > (See the list of subsystem names on the web dashboard) > > If the report is a duplicate of another one, reply with: > #syz dup: exact-subject-of-another-report > > If you want to undo deduplication, reply with: > #syz undup
