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

goroutine 17 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc000838100, 0xc000715740, 0xbf76c0, 0x0, 0xc000715700)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).mutate(0xbf76c0, 0xc000838100, 0xc000715740, 0x8fa9e0, 0xc000458b40, 0xc000715108, 0xc000458840, 0x0, 0xc000459200, 0x1da928ebed2e16af, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:264 +0x533
github.com/google/syzkaller/prog.(*Target).mutateArg(0xc0000731e0, 0xc000838100, 0xc000715740, 0x8fa9e0, 0xc000458b40, 0xc000715108, 0xc000458840, 0x0, 0x4f0f00, 0xc000771e0f, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:172 +0xe3
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000771ed0, 0xa)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:153 +0x231
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc000714c80, 0x8f8660, 0xc0006f16e0, 0x1e, 0xc00026bec0, 0xc00065c000, 0x8fd, 0x900)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:34 +0x2db
main.(*Proc).loop(0xc00026bf40)
	/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