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

goroutine 17 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc000524360, 0xc000639c40, 0xbf76c0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).mutate(0xbf76c0, 0xc000524360, 0xc000639c40, 0x8fa9e0, 0xc0004e8810, 0xc000639ac8, 0xc0004e87e0, 0x0, 0xc0004e8900, 0x461906adf3400579, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:264 +0x533
github.com/google/syzkaller/prog.(*Target).mutateArg(0xc0000731e0, 0xc000524360, 0xc000639c40, 0x8fa9e0, 0xc0004e8810, 0xc000639ac8, 0xc0004e87e0, 0x0, 0x4f0f00, 0xc000827e0f, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:172 +0xe3
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000827ed0, 0xa)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:153 +0x231
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc000639a00, 0x8f8660, 0xc0006a5440, 0x1e, 0xc0006054c0, 0xc00026c000, 0x98a, 0xc00)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:34 +0x2db
main.(*Proc).loop(0xc000605540)
	/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