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

goroutine 16 [running]:
github.com/google/syzkaller/prog.(*randGen).filename(0xc0006669a0, 0xc0004cf3c0, 0xbf4ce0, 0x8, 0x20)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:161 +0x2ac
github.com/google/syzkaller/prog.(*BufferType).generate(0xbf4ce0, 0xc0006669a0, 0xc0004cf3c0, 0xc00007b500, 0xfd2fbc919bad659, 0xc0007339e8, 0x4f0c53, 0xc0006f63c0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:646 +0x4fc
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc0006669a0, 0xc0004cf3c0, 0x8fd600, 0xbf4ce0, 0x100, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:581 +0x1b6
github.com/google/syzkaller/prog.(*randGen).generateArg(0xc0006669a0, 0xc0004cf3c0, 0x8fd600, 0xbf4ce0, 0x8, 0x8fa9e0, 0x7437b2, 0x87a299, 0x3)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*PtrType).generate(0xbd18a0, 0xc0006669a0, 0xc0004cf3c0, 0x8faa60, 0xc000615bf0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:729 +0x84
github.com/google/syzkaller/prog.(*randGen).generateArgImpl(0xc0006669a0, 0xc0004cf3c0, 0x8fda60, 0xbd18a0, 0xc000733b00, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:581 +0x1b6
github.com/google/syzkaller/prog.(*randGen).generateArg(0xc0006669a0, 0xc0004cf3c0, 0x8fda60, 0xbd18a0, 0x0, 0x0, 0x0, 0x0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:530 +0x52
github.com/google/syzkaller/prog.(*randGen).generateArgs(0xc0006669a0, 0xc0004cf3c0, 0xbc6800, 0x2, 0x2, 0x1d04ef5a1e6109e8, 0xc000733db0, 0x72beae, 0x7f3580, 0xc0004bd9b0, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:518 +0x11d
github.com/google/syzkaller/prog.(*randGen).generateParticularCall(0xc0006669a0, 0xc0004cf3c0, 0xbdd2a0, 0x69, 0xc0004cf3c0, 0xc0006153b0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:462 +0xd1
github.com/google/syzkaller/prog.(*randGen).generateCall(0xc0006669a0, 0xc0004cf3c0, 0xc0004ce8c0, 0xc0004cf3c0, 0xc000733e48, 0x7311e7)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/rand.go:454 +0xa4
github.com/google/syzkaller/prog.(*mutator).insertCall(0xc000733ed0, 0x14)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:118 +0xcb
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0004ce8c0, 0x8f8660, 0xc0006f63c0, 0x1e, 0xc000762bc0, 0xc0006b2000, 0x9fe, 0xc00)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:32 +0x299
main.(*Proc).loop(0xc000762d80)
	/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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