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

goroutine 16 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc0006ba300, 0xc0006df7c0, 0xbf4c40, 0x0, 0xc0006df700)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).mutate(0xbf4c40, 0xc0006ba300, 0xc0006df7c0, 0x8fa9e0, 0xc000737500, 0xc0006df788, 0xc0007374d0, 0x0, 0xc000737900, 0xac3dd492c03232e, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:264 +0x533
github.com/google/syzkaller/prog.(*Target).mutateArg(0xc0000711e0, 0xc0006ba300, 0xc0006df7c0, 0x8fa9e0, 0xc000737500, 0xc0006df788, 0xc0007374d0, 0x0, 0x4f0f00, 0xc000577e0f, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:172 +0xe3
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000577ed0, 0xa)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:153 +0x231
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0006df740, 0x8f8660, 0xc0003e2030, 0x1e, 0xc0004ef680, 0xc000836000, 0x771, 0x900)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:34 +0x2db
main.(*Proc).loop(0xc00045a240)
	/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