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lookup: handle // and trailing slash components correctly
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When we hit empty components, we need to treat them as though they are a
"." component. We could skip them for non-trailing components but for
trailing components it's critical to actually try to do the open so that
we get openat2-like errors for non-directory states.

For the single trailing slash case, it's simpler to implement it as a
final "." open after we've done the other lookups (we could switch to
using an array of path component like libpathrs does, but this is a
simpler change).

Signed-off-by: Aleksa Sarai <[email protected]>
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@cyphar
cyphar committed Jul 23, 2024
1 parent ecd61ca commit f29b7a4
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39 changes: 29 additions & 10 deletions lookup_linux.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,11 @@ func (s *symlinkStack) popPart(part string) error {
// real path provided by the user, and this is a no-op.
return errEmptyStack
}
if part == "." {
// "." components are no-ops -- we drop them when doing SwapLink.
return nil
}

tailEntry := (*s)[len(*s)-1]

// Double-check that we are popping the component we expect.
Expand Down Expand Up @@ -110,14 +115,7 @@ func (s *symlinkStack) push(dir *os.File, remainingPath, linkTarget string) erro
// Split the link target and clean up any "" parts.
linkTargetParts := slices.DeleteFunc(
strings.Split(linkTarget, "/"),
func(part string) bool { return part == "" })

// Don't add a no-op link to the stack. You can't create a no-op link
// symlink, but if the symlink is /, partialLookupInRoot has already jumped to the
// root and so there's nothing more to do.
if len(linkTargetParts) == 0 {
return nil
}
func(part string) bool { return part == "" || part == "." })

// Copy the directory so the caller doesn't close our copy.
dirCopy, err := dupFile(dir)
Expand Down Expand Up @@ -244,9 +242,11 @@ func lookupInRoot(root *os.File, unsafePath string, partial bool) (Handle *os.Fi
} else {
part, remainingPath = remainingPath[:i], remainingPath[i+1:]
}
// Skip any "//" components.
// If we hit an empty component, we need to treat it as though it is
// "." so that trailing "/" and "//" components on a non-directory
// correctly return the right error code.
if part == "" {
continue
part = "."
}

// Apply the component lexically to the path we are building.
Expand Down Expand Up @@ -365,6 +365,25 @@ func lookupInRoot(root *os.File, unsafePath string, partial bool) (Handle *os.Fi
return currentDir, oldRemainingPath, err
}
}

// If the unsafePath had a trailing slash, we need to make sure we try to
// do a relative "." open so that we will correctly return an error when
// the final component is a non-directory (to match openat2). In the
// context of openat2, a trailing slash and a trailing "/." are completely
// equivalent.
if strings.HasSuffix(unsafePath, "/") {
nextDir, err := openatFile(currentDir, ".", unix.O_PATH|unix.O_NOFOLLOW|unix.O_CLOEXEC, 0)
if err != nil {
if !partial {
_ = currentDir.Close()
currentDir = nil
}
return currentDir, "", err
}
_ = currentDir.Close()
currentDir = nextDir
}

// All of the components existed!
return currentDir, "", nil
}
88 changes: 55 additions & 33 deletions lookup_linux_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -153,55 +153,86 @@ func testPartialLookup(t *testing.T, partialLookupFn partialLookupFunc) {
// Complete lookups.
"complete-dir1": {"a", lookupResult{handlePath: "/a", remainingPath: "", fileType: unix.S_IFDIR}},
"complete-dir2": {"b/c/d/e/f", lookupResult{handlePath: "/b/c/d/e/f", remainingPath: "", fileType: unix.S_IFDIR}},
"complete-dir3": {"b///././c////.//d/./././///e////.//./f//././././", lookupResult{handlePath: "/b/c/d/e/f", remainingPath: "", fileType: unix.S_IFDIR}},
"complete-fifo": {"b/fifo", lookupResult{handlePath: "/b/fifo", remainingPath: "", fileType: unix.S_IFIFO}},
"complete-sock": {"b/sock", lookupResult{handlePath: "/b/sock", remainingPath: "", fileType: unix.S_IFSOCK}},
// Partial lookups.
"partial-dir-basic": {"a/b/c/d/e/f/g/h", lookupResult{handlePath: "/a", remainingPath: "b/c/d/e/f/g/h", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"partial-dir-dotdot": {"a/foo/../bar/baz", lookupResult{handlePath: "/a", remainingPath: "foo/../bar/baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
// Complete lookups of non-lexical symlinks.
"nonlexical-basic-complete": {"target", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-basic-complete1": {"target", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-basic-complete2": {"target/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-basic-complete3": {"target//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-basic-partial": {"target/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-basic-partial-dotdot": {"target/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level1-abs-complete": {"link1/target_abs", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level1-abs-complete1": {"link1/target_abs", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level1-abs-complete2": {"link1/target_abs/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level1-abs-complete3": {"link1/target_abs//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level1-abs-partial": {"link1/target_abs/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level1-abs-partial-dotdot": {"link1/target_abs/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level1-rel-complete": {"link1/target_rel", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level1-rel-complete1": {"link1/target_rel", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level1-rel-complete2": {"link1/target_rel/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level1-rel-complete3": {"link1/target_rel//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level1-rel-partial": {"link1/target_rel/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level1-rel-partial-dotdot": {"link1/target_rel/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-abs-abs-complete": {"link2/link1_abs/target_abs", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-abs-complete1": {"link2/link1_abs/target_abs", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-abs-complete2": {"link2/link1_abs/target_abs/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-abs-complete3": {"link2/link1_abs/target_abs//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-abs-partial": {"link2/link1_abs/target_abs/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-abs-abs-partial-dotdot": {"link2/link1_abs/target_abs/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-abs-rel-complete": {"link2/link1_abs/target_rel", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-rel-complete1": {"link2/link1_abs/target_rel", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-rel-complete2": {"link2/link1_abs/target_rel/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-rel-complete3": {"link2/link1_abs/target_rel//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-rel-partial": {"link2/link1_abs/target_rel/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-abs-rel-partial-dotdot": {"link2/link1_abs/target_rel/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-abs-open-complete": {"link2/link1_abs/../target", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-open-complete1": {"link2/link1_abs/../target", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-open-complete2": {"link2/link1_abs/../target/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-open-complete3": {"link2/link1_abs/../target//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-abs-open-partial": {"link2/link1_abs/../target/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-abs-open-partial-dotdot": {"link2/link1_abs/../target/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-rel-abs-complete": {"link2/link1_rel/target_abs", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-abs-complete1": {"link2/link1_rel/target_abs", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-abs-complete2": {"link2/link1_rel/target_abs/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-abs-complete3": {"link2/link1_rel/target_abs//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-abs-partial": {"link2/link1_rel/target_abs/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-rel-abs-partial-dotdot": {"link2/link1_rel/target_abs/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-rel-rel-complete": {"link2/link1_rel/target_rel", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-rel-complete1": {"link2/link1_rel/target_rel", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-rel-complete2": {"link2/link1_rel/target_rel/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-rel-complete3": {"link2/link1_rel/target_rel//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-rel-partial": {"link2/link1_rel/target_rel/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-rel-rel-partial-dotdot": {"link2/link1_rel/target_rel/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-rel-open-complete": {"link2/link1_rel/../target", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-open-complete1": {"link2/link1_rel/../target", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-open-complete2": {"link2/link1_rel/../target/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-open-complete3": {"link2/link1_rel/../target//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level2-rel-open-partial": {"link2/link1_rel/../target/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level2-rel-open-partial-dotdot": {"link2/link1_rel/../target/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level3-abs-complete": {"link3/target_abs", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level3-abs-complete1": {"link3/target_abs", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level3-abs-complete2": {"link3/target_abs/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level3-abs-complete3": {"link3/target_abs//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level3-abs-partial": {"link3/target_abs/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level3-abs-partial-dotdot": {"link3/target_abs/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level3-rel-complete": {"link3/target_rel", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level3-rel-complete1": {"link3/target_rel", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level3-rel-complete2": {"link3/target_rel/", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level3-rel-complete3": {"link3/target_rel//", lookupResult{handlePath: "/target", remainingPath: "", fileType: unix.S_IFDIR}},
"nonlexical-level3-rel-partial": {"link3/target_rel/foo", lookupResult{handlePath: "/target", remainingPath: "foo", fileType: unix.S_IFDIR, err: unix.ENOENT}},
"nonlexical-level3-rel-partial-dotdot": {"link3/target_rel/../target/foo/bar/../baz", lookupResult{handlePath: "/target", remainingPath: "foo/bar/../baz", fileType: unix.S_IFDIR, err: unix.ENOENT}},
// Partial lookups due to hitting a non-directory.
"partial-nondir-slash1": {"b/c/file/", lookupResult{handlePath: "/b/c/file", remainingPath: "", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-nondir-slash2": {"b/c/file//", lookupResult{handlePath: "/b/c/file", remainingPath: "/", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-nondir-dot": {"b/c/file/.", lookupResult{handlePath: "/b/c/file", remainingPath: ".", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-nondir-dotdot1": {"b/c/file/..", lookupResult{handlePath: "/b/c/file", remainingPath: "..", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-nondir-dotdot2": {"b/c/file/../foo/bar", lookupResult{handlePath: "/b/c/file", remainingPath: "../foo/bar", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-nondir-symlink-slash1": {"b-file/", lookupResult{handlePath: "/b/c/file", remainingPath: "", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-nondir-symlink-slash2": {"b-file//", lookupResult{handlePath: "/b/c/file", remainingPath: "/", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-nondir-symlink-dot": {"b-file/.", lookupResult{handlePath: "/b/c/file", remainingPath: ".", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-nondir-symlink-dotdot1": {"b-file/..", lookupResult{handlePath: "/b/c/file", remainingPath: "..", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-nondir-symlink-dotdot2": {"b-file/../foo/bar", lookupResult{handlePath: "/b/c/file", remainingPath: "../foo/bar", fileType: unix.S_IFREG, err: unix.ENOTDIR}},
"partial-fifo-slash1": {"b/fifo/", lookupResult{handlePath: "/b/fifo", remainingPath: "", fileType: unix.S_IFIFO, err: unix.ENOTDIR}},
"partial-fifo-slash2": {"b/fifo//", lookupResult{handlePath: "/b/fifo", remainingPath: "/", fileType: unix.S_IFIFO, err: unix.ENOTDIR}},
"partial-fifo-dot": {"b/fifo/.", lookupResult{handlePath: "/b/fifo", remainingPath: ".", fileType: unix.S_IFIFO, err: unix.ENOTDIR}},
"partial-fifo-dotdot1": {"b/fifo/..", lookupResult{handlePath: "/b/fifo", remainingPath: "..", fileType: unix.S_IFIFO, err: unix.ENOTDIR}},
"partial-fifo-dotdot2": {"b/fifo/../foo/bar", lookupResult{handlePath: "/b/fifo", remainingPath: "../foo/bar", fileType: unix.S_IFIFO, err: unix.ENOTDIR}},
"partial-sock-slash1": {"b/sock/", lookupResult{handlePath: "/b/sock", remainingPath: "", fileType: unix.S_IFSOCK, err: unix.ENOTDIR}},
"partial-sock-slash2": {"b/sock//", lookupResult{handlePath: "/b/sock", remainingPath: "/", fileType: unix.S_IFSOCK, err: unix.ENOTDIR}},
"partial-sock-dot": {"b/sock/.", lookupResult{handlePath: "/b/sock", remainingPath: ".", fileType: unix.S_IFSOCK, err: unix.ENOTDIR}},
"partial-sock-dotdot1": {"b/sock/..", lookupResult{handlePath: "/b/sock", remainingPath: "..", fileType: unix.S_IFSOCK, err: unix.ENOTDIR}},
"partial-sock-dotdot2": {"b/sock/../foo/bar", lookupResult{handlePath: "/b/sock", remainingPath: "../foo/bar", fileType: unix.S_IFSOCK, err: unix.ENOTDIR}},
Expand Down Expand Up @@ -747,7 +778,7 @@ func TestSymlinkStackTailChain(t *testing.T) {
defer ss.Close()

// Basic expected contents.
testStackContents(t, "initial state", ss,
initialState := []expectedStackEntry{
// Top entry is not a tail-chain.
expectedStackEntry{"A", []string{"subdir1"}},
// The first tail-chain should have no unwalked links.
Expand All @@ -764,31 +795,22 @@ func TestSymlinkStackTailChain(t *testing.T) {
expectedStackEntry{"J", nil},
// Final entry in the second tail-chain.
expectedStackEntry{"K", []string{"taillink2", ".."}},
)
}

testStackContents(t, "initial state", ss, initialState...)

// Trying to pop "." does nothing.
for i := 0; i < 20; i++ {
require.NoError(t, ss.PopPart("."), `popping "." should never fail`)
// NOTE: Same contents as above.
testStackContents(t, "noop pop .", ss, initialState...)
}

// Popping any of the early tail chain entries must fail.
for _, badPart := range []string{"subdir1", "subdir2", "..", "."} {
for _, badPart := range []string{"subdir1", "subdir2", ".."} {
require.ErrorIsf(t, ss.PopPart(badPart), errBrokenSymlinkStack, "bad pop %q", badPart)

// NOTE: Same contents as above.
testStackContents(t, "bad pop "+badPart, ss,
// Top entry is not a tail-chain.
expectedStackEntry{"A", []string{"subdir1"}},
// The first tail-chain should have no unwalked links.
expectedStackEntry{"B", nil},
expectedStackEntry{"C", nil},
expectedStackEntry{"D", nil},
// Final entry in the first tail-chain.
expectedStackEntry{"E", []string{"subdir2"}},
// The second tail-chain should have no unwalked links.
expectedStackEntry{"F", nil},
expectedStackEntry{"G", nil},
expectedStackEntry{"H", nil},
expectedStackEntry{"I", nil},
expectedStackEntry{"J", nil},
// Final entry in the second tail-chain.
expectedStackEntry{"K", []string{"taillink2", ".."}},
)
testStackContents(t, "bad pop "+badPart, ss, initialState...)
}

// Dropping the second-last entry should keep the tail-chain.
Expand Down
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