On Mon, Mar 2, 2020 at 2:35 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > > On Mon, Mar 2, 2020 at 1:10 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > On Sun, Mar 1, 2020 at 9:13 PM syzbot > > > > <syzbot+66a9752fa927f745385e@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > Hello, > > > > > > > > > > syzbot found the following crash on: > > > > > > > > > > HEAD commit: f8788d86 Linux 5.6-rc3 > > > > > git tree: upstream > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=13c5f8f9e00000 > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=5d2e033af114153f > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=66a9752fa927f745385e > > > > > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=131d9a81e00000 > > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14117a81e00000 > > > > > > > > > > > > > Dmitry, > > > > > > > > There is something strange about the C repro. > > > > It passes an invalid address for the first arg of mount syscall: > > > > > > > > syscall(__NR_mount, 0x400000ul, 0x20000000ul, 0x20000080ul, 0ul, > > > > 0x20000100ul); > > > > > > > > With this address mount syscall returns -EFAULT on my system. > > > > I fixed this manually, but repro did not trigger the reported bug on my system. > > > > > > Hi Amir, > > > > > > This is not strange in the context of fuzzer, it's goal is to pass > > > random data. Generally if it says 0x400000ul, that's what it is, don't > > > fix it, or you are running a different program that may not reproduce > > > the bug. If syzbot attaches a reproducer, the bug was triggered by > > > precisely this program. > > > > > > > What's strange it that a bug in overlay code cannot be triggered if overlay > > isn't mounted and as it is the repro couldn't mount overlayfs at all, at > > lease with my kernel config. > > Can it depend on kernel config? The bug was triggered by the program > provided somehow. I am not sure. I do not have CONFIG_HARDENED_USERCOPY set. > > Separate question: why is it failing? Isn't src unused for overlayfs? > Where/how does vfs code look at src? > SYSCALL_DEFINE5(mount, ... copy_mount_string(dev_name) strndup_user() memdup_user() copy_from_user() Not in overlayfs code. Actually, the source (dev) is not used by overlayfs but is visible at /proc/mounts. Thanks, Amir.
