panic: sandbox escaping file name "../file0"

goroutine 16 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc0008562a0, 0xc000848840, 0xbf4c40, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).mutate(0xbf4c40, 0xc0008562a0, 0xc000848840, 0x8fa9e0, 0xc00083f9e0, 0xc000848808, 0xc00083f9b0, 0x0, 0xc00083fa00, 0x72235695a8ce4f78, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:264 +0x533
github.com/google/syzkaller/prog.(*Target).mutateArg(0xc0000731e0, 0xc0008562a0, 0xc000848840, 0x8fa9e0, 0xc00083f9e0, 0xc000848808, 0xc00083f9b0, 0x0, 0x4f0f00, 0xc000675e0f, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:172 +0xe3
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000675ed0, 0xa)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:153 +0x231
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0008487c0, 0x8f8660, 0xc000692630, 0x1e, 0xc0002f96c0, 0xc0006d2000, 0x934, 0xc00)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:34 +0x2db
main.(*Proc).loop(0xc0002f9880)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:99 +0x446created by main.main
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/fuzzer.go:236 +0xfe2