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

goroutine 16 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc00073afe0, 0xc0006d0a00, 0xbf5000, 0x203000, 0xc00075b918)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).generate(0xbf5000, 0xc00073afe0, 0xc0006d0a00, 0xc000079500, 0x61af7d0cc51aa32b, 0xc0008659e8, 0x4f0c53, 0xc000750e40)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:646 +0x4fc
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc00073afe0, 0xc0006d0a00, 0x8fd600, 0xbf5000, 0x200, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:581 +0x1b6
github.com/google/syzkaller/prog.(*randGen).generateArg(0xc00073afe0, 0xc0006d0a00, 0x8fd600, 0xbf5000, 0xaaaaaaaaaaaaaaaa, 0x38, 0x7437b2, 0x87a299, 0x3)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*PtrType).generate(0xbd1d80, 0xc00073afe0, 0xc0006d0a00, 0x40b7ff, 0xc00073b220, 0x20, 0x20, 0x8115a0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:729 +0x84
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc00073afe0, 0xc0006d0a00, 0x8fda60, 0xbd1d80, 0xc000865b00, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:581 +0x1b6
github.com/google/syzkaller/prog.(*randGen).generateArg(0xc00073afe0, 0xc0006d0a00, 0x8fda60, 0xbd1d80, 0x2, 0x2, 0x0, 0x203000, 0xc000865ce8)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*randGen).generateArgs(0xc00073afe0, 0xc0006d0a00, 0xbc6860, 0x2, 0x2, 0x19b796f999e98ea0, 0xc000865db0, 0x72beae, 0x7f3580, 0xc000750270, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:518 +0x11d
github.com/google/syzkaller/prog.(*randGen).generateParticularCall(0xc00073afe0, 0xc0006d0a00, 0xbdd5a0, 0x71, 0xc0006d0a00, 0xc0007518c0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:462 +0xd1
github.com/google/syzkaller/prog.(*randGen).generateCall(0xc00073afe0, 0xc0006d0a00, 0xc0006d07c0, 0xc0006d0a00, 0xc000865e48, 0x7311e7)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:454 +0xa4
github.com/google/syzkaller/prog.(*mutator).insertCall(0xc000865ed0, 0x14)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:118 +0xcb
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0006d07c0, 0x8f8660, 0xc000750e40, 0x1e, 0xc00072dd00, 0xc0006d4000, 0x9e3, 0xc00)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:32 +0x299
main.(*Proc).loop(0xc00072dd40)
	/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