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

goroutine 16 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc00067fbe0, 0xc00045b240, 0xbf4c40, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).mutate(0xbf4c40, 0xc00067fbe0, 0xc00045b240, 0x8fa9e0, 0xc00067c5a0, 0xc00045b208, 0xc00067c570, 0x0, 0xc00067c600, 0x7ba466b14cf2b768, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:264 +0x533
github.com/google/syzkaller/prog.(*Target).mutateArg(0xc0000731e0, 0xc00067fbe0, 0xc00045b240, 0x8fa9e0, 0xc00067c5a0, 0xc00045b208, 0xc00067c570, 0x0, 0x4f0f00, 0xc00082be0f, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:172 +0xe3
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc00082bed0, 0xa)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:153 +0x231
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc00045b1c0, 0x8f8660, 0xc000641cb0, 0x1e, 0xc00063fa80, 0xc0006c4000, 0x92b, 0xc00)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:34 +0x2db
main.(*Proc).loop(0xc00063fac0)
	/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
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