On Mon, Dec 17, 2018 at 8:21 AM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > On Sun, Dec 16, 2018 at 10:11:04PM -0800, syzbot wrote: > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: d14b746c6c1c Add linux-next specific files for 20181214 > > git tree: linux-next > > console output: https://syzkaller.appspot.com/x/log.txt?x=13706347400000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=1da6d2d18f803140 > > dashboard link: https://syzkaller.appspot.com/bug?extid=5399ed0832693e29f392 > > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101032b3400000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16534063400000 > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+5399ed0832693e29f392@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > slab_pre_alloc_hook mm/slab.h:423 [inline] > > slab_alloc mm/slab.c:3365 [inline] > > kmem_cache_alloc+0x2c4/0x730 mm/slab.c:3539 > > __d_alloc+0xc8/0xb90 fs/dcache.c:1599 > > ------------[ cut here ]------------ > > kernel BUG at fs/inode.c:1566! > > d_alloc_anon fs/dcache.c:1698 [inline] > > d_make_root+0x43/0xc0 fs/dcache.c:1885 > > autofs_fill_super+0x6f1/0x1c30 fs/autofs/inode.c:273 > > Huh? BUG is in iput(), AFAICS, so the stack trace is rather misreported. Yes, it's a known problem that kernel is generally incapable of producing parsable crash reports. I think Tetsuo is working on a solution, but it takes very large amount of discussions and months of time. > iput() can be called by d_make_root(), provided that dentry allocation > fails. So the most straightforward interpretation would be that we > had an allocation failure (injected?), followed by iput() of the inode > passed to d_make_root(). Which happened to find I_CLEAR in ->i_state > of that inode somehow, which should be impossible short of seriously > buggered inode refcounting somewhere - the inode has just been returned > by new_inode(), which clears i_state, and it would have to have passed > clear_inode() (i.e. has been through inode eviction) since then... Yes, there are injected failures in the log. And the repro says: #{..."fault":true,"fault_call":1,"fault_nth":36 ...} mkdir(&(0x7f0000000140)='./file0\x00', 0x0) mount(0x0, &(0x7f0000000100)='./file0\x00', &(0x7f0000000180)='autofs\x00', 0x0, 0x0) Since the repro is single-threaded, I would expect that the bug is directly on the error handling path of the failure allocation.
