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

goroutine 17 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc0004e3460, 0xc00066c740, 0xbf69a0, 0xc000220a80, 0xc000061a38)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).generate(0xbf69a0, 0xc0004e3460, 0xc00066c740, 0xc000469500, 0x7415d7dfc3a801cc, 0xc00023d9e8, 0x4f0c53, 0xc00023f440)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:646 +0x4fc
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc0004e3460, 0xc00066c740, 0x8fd600, 0xbf69a0, 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(0xc0004e3460, 0xc00066c740, 0x8fd600, 0xbf69a0, 0xaaaaaaaaaaaaaaaa, 0x38, 0x7437b2, 0x87a299, 0x3)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*PtrType).generate(0xbd61c0, 0xc0004e3460, 0xc00066c740, 0x40b7ff, 0xc0004e3660, 0x20, 0x20, 0x8115a0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:729 +0x84
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc0004e3460, 0xc00066c740, 0x8fda60, 0xbd61c0, 0xc00023db00, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:581 +0x1b6
github.com/google/syzkaller/prog.(*randGen).generateArg(0xc0004e3460, 0xc00066c740, 0x8fda60, 0xbd61c0, 0x2, 0x2, 0x0, 0x203000, 0xc00023dce8)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*randGen).generateArgs(0xc0004e3460, 0xc00066c740, 0xbc6d40, 0x2, 0x2, 0x7143a025f02fc542, 0xc00023ddb0, 0x72beae, 0x7f3580, 0xc00023e840, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:518 +0x11d
github.com/google/syzkaller/prog.(*randGen).generateParticularCall(0xc0004e3460, 0xc00066c740, 0xbdfe80, 0xd4, 0xc00066c740, 0xc00000d680)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:462 +0xd1
github.com/google/syzkaller/prog.(*randGen).generateCall(0xc0004e3460, 0xc00066c740, 0xc00066c6c0, 0xc00066c740, 0xc00023de48, 0x7311e7)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:454 +0xa4
github.com/google/syzkaller/prog.(*mutator).insertCall(0xc00023ded0, 0x14)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:118 +0xcb
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc00066c6c0, 0x8f8660, 0xc00023f440, 0x1e, 0xc000235200, 0xc0006d8000, 0x52e, 0x6a0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:32 +0x299
main.(*Proc).loop(0xc000235280)
	/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