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

goroutine 16 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc0009a4540, 0xc00077e8c0, 0xbf76c0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).mutate(0xbf76c0, 0xc0009a4540, 0xc00077e8c0, 0x8fa9e0, 0xc0008271d0, 0xc00077e008, 0xc0008271a0, 0x0, 0xc000827600, 0x3703750f5b1f3d1b, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:264 +0x533
github.com/google/syzkaller/prog.(*Target).mutateArg(0xc0000711e0, 0xc0009a4540, 0xc00077e8c0, 0x8fa9e0, 0xc0008271d0, 0xc00077e008, 0xc0008271a0, 0x0, 0x4f0f00, 0xc0007cfe0f, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:172 +0xe3
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc0007cfed0, 0xa)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:153 +0x231
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc00071ff40, 0x8f8660, 0xc00054af90, 0x1e, 0xc00071e200, 0xc00066e000, 0xa5b, 0xc00)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:34 +0x2db
main.(*Proc).loop(0xc00071e240)
	/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
login: