On Wed, Jun 10, 2020 at 08:23:33PM +0900, Tetsuo Handa wrote: > On 2020/06/10 19:56, syzbot wrote: > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: 7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=16e12212100000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=d195fe572fb15312 > > dashboard link: https://syzkaller.appspot.com/bug?extid=4abac52934a48af5ff19 > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > Unfortunately, I don't have any reproducer for this crash yet. > > The report says proc_sb_info(sb) == NULL at proc_kill_sb() which was called via > fs->kill_sb(s) from deactivate_locked_super(). The console log says that memory > allocation for proc_sb_info(sb) failed due to memory allocation fault injection. > > [ 1492.052802][ T6840] FAULT_INJECTION: forcing a failure. > [ 1492.052802][ T6840] name failslab, interval 1, probability 0, space 0, times 0 > [ 1492.077153][ T6840] CPU: 0 PID: 6840 Comm: syz-executor.2 Not tainted 5.7.0-syzkaller #0 > [ 1492.085449][ T6840] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > [ 1492.095511][ T6840] Call Trace: > [ 1492.098811][ T6840] dump_stack+0x188/0x20d > [ 1492.103157][ T6840] should_fail.cold+0x5/0xa > [ 1492.107686][ T6840] ? fault_create_debugfs_attr+0x140/0x140 > [ 1492.107721][ T6840] ? idr_replace+0xee/0x160 > [ 1492.127210][ T6840] should_failslab+0x5/0xf > [ 1492.131638][ T6840] kmem_cache_alloc_trace+0x2d0/0x7d0 > [ 1492.137020][ T6840] ? up_write+0x148/0x470 > [ 1492.141367][ T6840] proc_fill_super+0x79/0x5c0 > [ 1492.146052][ T6840] ? proc_parse_param+0x8a0/0x8a0 > [ 1492.151092][ T6840] vfs_get_super+0x12e/0x2d0 > [ 1492.155694][ T6840] vfs_get_tree+0x89/0x2f0 > [ 1492.160126][ T6840] do_mount+0x1306/0x1b40 > [ 1492.164467][ T6840] ? copy_mount_string+0x40/0x40 > [ 1492.169411][ T6840] ? __might_fault+0x190/0x1d0 > [ 1492.174188][ T6840] ? _copy_from_user+0x13c/0x1a0 > [ 1492.179138][ T6840] ? memdup_user+0x7c/0xd0 > [ 1492.183575][ T6840] __x64_sys_mount+0x18f/0x230 > [ 1492.188351][ T6840] do_syscall_64+0xf6/0x7d0 > [ 1492.192861][ T6840] entry_SYSCALL_64_after_hwframe+0x49/0xb3 > [ 1492.198759][ T6840] RIP: 0033:0x45ca69 > > That is, proc_kill_sb() was assuming "s->s_fs_info = fs_info;" is always > called from proc_fill_super() which is called via fill_super(sb, fc); from > vfs_get_super(). Yes. If fill_super() fails before filling up fs_info, deactivate_locked_super() will be called and sb->s_fs_info may be NULL. -- Rgrds, legion
