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Cover symlink attacks with test cases

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This commit is contained in:
Dane Everitt 2020-10-01 21:13:42 -07:00
parent 90ae815b1d
commit e3e89a2ecc
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GPG Key ID: EEA66103B3D71F53
2 changed files with 208 additions and 1 deletions
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2
server/filesystem/filesystem.go
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@ -332,7 +332,7 @@ func (fs *Filesystem) Delete(p string) error {
return errors.New("cannot delete root server directory")
}
if st, err := os.Stat(resolved); err != nil {
if st, err := os.Lstat(resolved); err != nil {
if !os.IsNotExist(err) {
fs.error(err).Warn("error while attempting to stat file before deletion")
}

207
server/filesystem/filesystem_test.go
View File

@ -80,6 +80,213 @@ func TestFilesystem_Path(t *testing.T) {
})
}
func TestFilesystem_SafePath(t *testing.T) {
g := Goblin(t)
fs, rfs := NewFs()
prefix := filepath.Join(rfs.root, "/server")
g.Describe("SafePath", func() {
g.It("returns a cleaned path to a given file", func() {
p, err := fs.SafePath("test.txt")
g.Assert(err).IsNil()
g.Assert(p).Equal(prefix + "/test.txt")
p, err = fs.SafePath("/test.txt")
g.Assert(err).IsNil()
g.Assert(p).Equal(prefix + "/test.txt")
p, err = fs.SafePath("./test.txt")
g.Assert(err).IsNil()
g.Assert(p).Equal(prefix + "/test.txt")
p, err = fs.SafePath("/foo/../test.txt")
g.Assert(err).IsNil()
g.Assert(p).Equal(prefix + "/test.txt")
p, err = fs.SafePath("/foo/bar")
g.Assert(err).IsNil()
g.Assert(p).Equal(prefix + "/foo/bar")
})
g.It("handles root directory access", func() {
p, err := fs.SafePath("/")
g.Assert(err).IsNil()
g.Assert(p).Equal(prefix)
p, err = fs.SafePath("")
g.Assert(err).IsNil()
g.Assert(p).Equal(prefix)
})
g.It("removes trailing slashes from paths", func() {
p, err := fs.SafePath("/foo/bar/")
g.Assert(err).IsNil()
g.Assert(p).Equal(prefix + "/foo/bar")
})
g.It("handles deeply nested directories that do not exist", func() {
p, err := fs.SafePath("/foo/bar/baz/quaz/../../ducks/testing.txt")
g.Assert(err).IsNil()
g.Assert(p).Equal(prefix + "/foo/bar/ducks/testing.txt")
})
g.It("blocks access to files outside the root directory", func() {
p, err := fs.SafePath("../test.txt")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
g.Assert(p).Equal("")
p, err = fs.SafePath("/../test.txt")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
g.Assert(p).Equal("")
p, err = fs.SafePath("./foo/../../test.txt")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
g.Assert(p).Equal("")
p, err = fs.SafePath("..")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
g.Assert(p).Equal("")
})
})
}
// We test against accessing files outside the root directory in the tests, however it
// is still possible for someone to mess up and not properly use this safe path call. In
// order to truly confirm this, we'll try to pass in a symlinked malicious file to all of
// the calls and ensure they all fail with the same reason.
func TestFilesystem_Blocks_Symlinks(t *testing.T) {
g := Goblin(t)
fs, rfs := NewFs()
if err := rfs.CreateServerFile("/../malicious.txt", "external content"); err != nil {
panic(err)
}
if err := os.Mkdir(filepath.Join(rfs.root, "/malicious_dir"), 0777); err != nil {
panic(err)
}
if err := os.Symlink(filepath.Join(rfs.root, "malicious.txt"), filepath.Join(rfs.root, "/server/symlinked.txt")); err != nil {
panic(err)
}
if err := os.Symlink(filepath.Join(rfs.root, "/malicious_dir"), filepath.Join(rfs.root, "/server/external_dir")); err != nil {
panic(err)
}
g.Describe("Readfile", func() {
g.It("cannot read a file symlinked outside the root", func() {
b := bytes.Buffer{}
err := fs.Readfile("symlinked.txt", &b)
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
})
g.Describe("Writefile", func() {
g.It("cannot write to a file symlinked outside the root", func() {
r := bytes.NewReader([]byte("testing"))
err := fs.Writefile("symlinked.txt", r)
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
g.It("cannot write a file to a directory symlinked outside the root", func() {
r := bytes.NewReader([]byte("testing"))
err := fs.Writefile("external_dir/foo.txt", r)
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
})
g.Describe("CreateDirectory", func() {
g.It("cannot create a directory outside the root", func() {
err := fs.CreateDirectory("my_dir", "external_dir")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
g.It("cannot create a nested directory outside the root", func() {
err := fs.CreateDirectory("my/nested/dir", "external_dir/foo/bar")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
g.It("cannot create a nested directory outside the root", func() {
err := fs.CreateDirectory("my/nested/dir", "external_dir/server")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
})
g.Describe("Rename", func() {
g.It("cannot rename a file symlinked outside the directory root", func() {
err := fs.Rename("symlinked.txt", "foo.txt")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
g.It("cannot rename a symlinked directory outside the root", func() {
err := fs.Rename("external_dir", "foo")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
g.It("cannot rename a file to a location outside the directory root", func() {
rfs.CreateServerFile("my_file.txt", "internal content")
err := fs.Rename("my_file.txt", "external_dir/my_file.txt")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
})
g.Describe("Chown", func() {
g.It("cannot chown a file symlinked outside the directory root", func() {
err := fs.Chown("symlinked.txt")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
g.It("cannot chown a directory symlinked outside the directory root", func() {
err := fs.Chown("external_dir")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
})
g.Describe("Copy", func() {
g.It("cannot copy a file symlinked outside the directory root", func() {
err := fs.Copy("symlinked.txt")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, ErrBadPathResolution)).IsTrue()
})
})
g.Describe("Delete", func() {
g.It("deletes the symlinked file but leaves the source", func() {
err := fs.Delete("symlinked.txt")
g.Assert(err).IsNil()
_, err = os.Stat(filepath.Join(rfs.root, "malicious.txt"))
g.Assert(err).IsNil()
_, err = rfs.StatServerFile("symlinked.txt")
g.Assert(err).IsNotNil()
g.Assert(errors.Is(err, os.ErrNotExist)).IsTrue()
})
})
rfs.reset()
}
func TestFilesystem_Readfile(t *testing.T) {
g := Goblin(t)
fs, rfs := NewFs()