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

goroutine 17 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc00043f180, 0xc00022d900, 0xbf5640, 0x2, 0x2)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).generate(0xbf5640, 0xc00043f180, 0xc00022d900, 0xc00007aa00, 0x7b6a9af544d058c3, 0xc0007819e8, 0x4f0c53, 0xc000568360)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:646 +0x4fc
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc00043f180, 0xc00022d900, 0x8fd600, 0xbf5640, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:581 +0x1b6
github.com/google/syzkaller/prog.(*randGen).generateArg(0xc00043f180, 0xc00022d900, 0x8fd600, 0xbf5640, 0x0, 0x0, 0x7437b2, 0x87a299, 0x3)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*PtrType).generate(0xbd2a40, 0xc00043f180, 0xc00022d900, 0x8, 0x8, 0xc00000d920, 0x0, 0xc0000ed180)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:729 +0x84
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc00043f180, 0xc00022d900, 0x8fda60, 0xbd2a40, 0xc000781b00, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:581 +0x1b6
github.com/google/syzkaller/prog.(*randGen).generateArg(0xc00043f180, 0xc00022d900, 0x8fda60, 0xbd2a40, 0xc00000d908, 0x1, 0x1, 0x1, 0x1)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*randGen).generateArgs(0xc00043f180, 0xc00022d900, 0xbcf260, 0x4, 0x4, 0x6838668a6e68e832, 0xc000781db0, 0x72beae, 0x7f3580, 0xc00071b740, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:518 +0x11d
github.com/google/syzkaller/prog.(*randGen).generateParticularCall(0xc00043f180, 0xc00022d900, 0xbddea0, 0x87, 0xc00022d900, 0xc0005f5200)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:462 +0xd1
github.com/google/syzkaller/prog.(*randGen).generateCall(0xc00043f180, 0xc00022d900, 0xc000709a40, 0xc00022d900, 0xc000781e48, 0x7311e7)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:454 +0xa4
github.com/google/syzkaller/prog.(*mutator).insertCall(0xc000781ed0, 0x14)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:118 +0xcb
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc000709a40, 0x8f8660, 0xc000568360, 0x1e, 0xc0003c7800, 0xc000646000, 0x87f, 0x900)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:32 +0x299
main.(*Proc).loop(0xc0003c7880)
	/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