vole
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A free and open-source forge that lives in your Git repo.
Fuzz the parsers that read untrusted input
16bf0ebf8054de5044a52f93d156402542f0f71a · Keenan Nemetz · 10d ago · parent 70ba9a69
Fuzz the parsers that read untrusted input The SSH exec line, the Git HTTP route, and the LFS packet stream are all hand-written parsers on bytes a client controls, and each was covered only by a table of examples someone thought to write. Six targets, each asserting a property rather than waiting for a panic: the command parser cannot invent bytes and its output survives being quoted back, a route re-routes from its own parts and never names more than one path segment, a repository argument is a name and not a path, and the packet reader's lines survive being framed again. The seeds are the shapes the clients actually send, so go test ./... keeps guarding them and a fuzz target costs a push nothing. The route fuzzer found one gap on its first run: /git/.git/info/refs gave back an empty repository name with ok set, and only the store refused it. A route that answers ok now means a name the rest of the path applies to. Closes #96.
server/ssh/fuzz_test.go +123
| @@ -0,0 +1,123 @@ | |||
| 1 | package ssh | ||
| 2 | |||
| 3 | import ( | ||
| 4 | "strings" | ||
| 5 | "testing" | ||
| 6 | |||
| 7 | "github.com/rodent-software/vole/forge/repo" | ||
| 8 | ) | ||
| 9 | |||
| 10 | // FuzzSplitCommand drives the parser that turns an exec line from an | ||
| 11 | // unauthenticated connection into the argv the server acts on. The seeds are the | ||
| 12 | // shapes git actually sends, so `go test ./...` keeps refusing those; the | ||
| 13 | // fuzzer's job is everything between them. | ||
| 14 | // | ||
| 15 | // Two properties are checked, and neither is "it does not panic", which is the | ||
| 16 | // floor rather than the point: | ||
| 17 | // | ||
| 18 | // - It cannot invent bytes. Every byte of every argument came from the command | ||
| 19 | // line: a quote is consumed and writes nothing, an escape is consumed and | ||
| 20 | // writes one byte. | ||
| 21 | // - What it produces survives being written back out. The client builds these | ||
| 22 | // command lines, and the server parses them; if a value does not round-trip | ||
| 23 | // through git's quoting, one end misreads the other. | ||
| 24 | func FuzzSplitCommand(f *testing.F) { | ||
| 25 | for _, seed := range []string{ | ||
| 26 | "git-upload-pack '/demo.git'", | ||
| 27 | `git-upload-pack "/demo.git"`, | ||
| 28 | "git-receive-pack demo.git", | ||
| 29 | "git-upload-pack '/unterminated", | ||
| 30 | `git-upload-pack "half\`, | ||
| 31 | "git-upload-pack\t'demo.git'", | ||
| 32 | "git-upload-pack 'demo.git'", | ||
| 33 | "''", | ||
| 34 | "", | ||
| 35 | "vole-runner", | ||
| 36 | "vole-change-merge demo 01M5XCHRQFT0FTM0CJYRYWVD3V", | ||
| 37 | `git-upload-pack '/it'\''s.git'`, | ||
| 38 | } { | ||
| 39 | f.Add(seed) | ||
| 40 | } | ||
| 41 | f.Fuzz(func(t *testing.T, command string) { | ||
| 42 | argv, err := splitCommand(command) | ||
| 43 | if err != nil { | ||
| 44 | return | ||
| 45 | } | ||
| 46 | if total := argBytes(argv); total > len(command) { | ||
| 47 | t.Fatalf("splitCommand(%q) produced %d bytes of arguments from %d bytes", command, total, len(command)) | ||
| 48 | } | ||
| 49 | quoted := make([]string, len(argv)) | ||
| 50 | for i, arg := range argv { | ||
| 51 | quoted[i] = quoteArg(arg) | ||
| 52 | } | ||
| 53 | command2 := strings.Join(quoted, " ") | ||
| 54 | again, err := splitCommand(command2) | ||
| 55 | if err != nil { | ||
| 56 | t.Fatalf("re-quoted %q (from %q) does not parse: %v", command2, command, err) | ||
| 57 | } | ||
| 58 | if len(again) != len(argv) { | ||
| 59 | t.Fatalf("%q split to %d arguments, but %q splits to %d", command, len(argv), command2, len(again)) | ||
| 60 | } | ||
| 61 | for i := range argv { | ||
| 62 | if again[i] != argv[i] { | ||
| 63 | t.Fatalf("%q: argument %d is %q, but %q gives %q", command, i, argv[i], command2, again[i]) | ||
| 64 | } | ||
| 65 | } | ||
| 66 | }) | ||
| 67 | } | ||
| 68 | |||
| 69 | func argBytes(argv []string) int { | ||
| 70 | total := 0 | ||
| 71 | for _, arg := range argv { | ||
| 72 | total += len(arg) | ||
| 73 | } | ||
| 74 | return total | ||
| 75 | } | ||
| 76 | |||
| 77 | // quoteArg writes one argument the way git does: single quoted, with an embedded | ||
| 78 | // quote closing the quoting, escaping itself, and reopening it. | ||
| 79 | func quoteArg(arg string) string { | ||
| 80 | return "'" + strings.ReplaceAll(arg, "'", `'\''`) + "'" | ||
| 81 | } | ||
| 82 | |||
| 83 | // FuzzRepoName drives the step after parsing: the argument becomes a repository | ||
| 84 | // name, not a path. It is the same untrusted text, so it belongs with the parser | ||
| 85 | // that produces it — fuzzing one and not the other leaves the decision that | ||
| 86 | // actually touches storage untested. | ||
| 87 | func FuzzRepoName(f *testing.F) { | ||
| 88 | for _, seed := range []string{ | ||
| 89 | "/demo.git", | ||
| 90 | "demo.git", | ||
| 91 | "/demo", | ||
| 92 | "../demo.git", | ||
| 93 | "/a/b.git", | ||
| 94 | "/.git", | ||
| 95 | "/demo.git/", | ||
| 96 | "//demo.git", | ||
| 97 | "/demo.git/extra", | ||
| 98 | "/..git", | ||
| 99 | "/.a.git", | ||
| 100 | "", | ||
| 101 | } { | ||
| 102 | f.Add(seed) | ||
| 103 | } | ||
| 104 | f.Fuzz(func(t *testing.T, arg string) { | ||
| 105 | name, ok := repoName(arg) | ||
| 106 | if !ok { | ||
| 107 | return | ||
| 108 | } | ||
| 109 | // A name is one segment of a path under the repositories directory, so | ||
| 110 | // nothing that could climb or descend may survive as a name. | ||
| 111 | if strings.ContainsAny(name, "/\\") || strings.Contains(name, "..") { | ||
| 112 | t.Fatalf("repoName(%q) = %q, which is a path rather than a name", arg, name) | ||
| 113 | } | ||
| 114 | if err := repo.ValidateName(name); err != nil { | ||
| 115 | t.Fatalf("repoName(%q) = %q, which the repository store refuses: %v", arg, name, err) | ||
| 116 | } | ||
| 117 | // The name has to be the one git sends back for it. | ||
| 118 | again, ok := repoName("/" + name + ".git") | ||
| 119 | if !ok || again != name { | ||
| 120 | t.Fatalf("repoName(%q) = %q, but \"/%s.git\" gives %q, %v", arg, name, name, again, ok) | ||
| 121 | } | ||
| 122 | }) | ||
| 123 | } | ||