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

goroutine 16 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc000417c40, 0xc00070bb40, 0xbf4ec0, 0xbe7600, 0xc00021c2e0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).generate(0xbf4ec0, 0xc000417c40, 0xc00070bb40, 0xc00007b500, 0x2036f0fb8d9794d9, 0xc0005a39e8, 0x4f0c53, 0xc0004911a0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:646 +0x4fc
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc000417c40, 0xc00070bb40, 0x8fd600, 0xbf4ec0, 0xc000000200, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:581 +0x1b6
github.com/google/syzkaller/prog.(*randGen).generateArg(0xc000417c40, 0xc00070bb40, 0x8fd600, 0xbf4ec0, 0xaaaaaaaaaaaaaaaa, 0x38, 0x7437b2, 0x87a299, 0x3)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*PtrType).generate(0xbd1b40, 0xc000417c40, 0xc00070bb40, 0x40b7ff, 0xc00021c920, 0x20, 0x20, 0x8115a0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:729 +0x84
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc000417c40, 0xc00070bb40, 0x8fda60, 0xbd1b40, 0xc0005a3b00, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:581 +0x1b6
github.com/google/syzkaller/prog.(*randGen).generateArg(0xc000417c40, 0xc00070bb40, 0x8fda60, 0xbd1b40, 0x2, 0x2, 0x0, 0x203000, 0xc0005a3ce8)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*randGen).generateArgs(0xc000417c40, 0xc00070bb40, 0xbc6840, 0x2, 0x2, 0x4f46f4c6b17b6637, 0xc0005a3db0, 0x72beae, 0x7f3580, 0xc0004905d0, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:518 +0x11d
github.com/google/syzkaller/prog.(*randGen).generateParticularCall(0xc000417c40, 0xc00070bb40, 0xbdd420, 0x6d, 0xc00070bb40, 0xc00075dce0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:462 +0xd1
github.com/google/syzkaller/prog.(*randGen).generateCall(0xc000417c40, 0xc00070bb40, 0xc00070b300, 0xc00070bb40, 0xc0005a3e48, 0x7311e7)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:454 +0xa4
github.com/google/syzkaller/prog.(*mutator).insertCall(0xc0005a3ed0, 0x14)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:118 +0xcb
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc00070b300, 0x8f8660, 0xc0004911a0, 0x1e, 0xc0003e12c0, 0xc0007fc000, 0x6d3, 0x900)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:32 +0x299
main.(*Proc).loop(0xc0003e1300)
	/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