[PATCH] Allow globbing with unreadable parent directories

[Devin Hussey <husseydevin@xxxxxxxxx>]

POSIX specifies that when globbing, parent directories only have to be
searchable, not readable.

Previously, globbing using NO_CASE_GLOB would fail if any of the parent
directories in the path were not readable.

This was a major issue primarily affecting Termux, a Linux environment
for Android.

Termux's $HOME is "/data/data/com.termux/files/home", and the issue is
that "/data" and sometimes even "/" are not readable without system/root
permission.

This made every full path glob with NO_CASE_GLOB fail, breaking many
scripts such as the Prezto prompt.

Now, zsh will correctly glob even if the parent directory is not readable,
while respecting the searchable bit.

See:
 - https://github.com/sorin-ionescu/prezto/issues/1560
 - https://github.com/termux/termux-packages/issues/1894

Signed-off-by: Devin Hussey <husseydevin@xxxxxxxxx>
---
 Src/glob.c | 169 ++++++++++++++++++++++++++++-------------------------
 1 file changed, 89 insertions(+), 80 deletions(-)

diff --git a/Src/glob.c b/Src/glob.c
index bee890caf..4f5c2cf8b 100644
--- a/Src/glob.c
+++ b/Src/glob.c
@@ -580,100 +580,109 @@ scanner(Complist q, int shortcircuit)
     } else {
 	/* Do pattern matching on current path section. */
 	char *fn = pathbuf[pathbufcwd] ? unmeta(pathbuf + pathbufcwd) : ".";
-	int dirs = !!q->next;
-	DIR *lock = opendir(fn);
 	char *subdirs = NULL;
 	int subdirlen = 0;

-	if (lock == NULL)
+	/* First check for search permission. */
+	if (access(fn, X_OK) != 0)
 	    return;
-	while ((fn = zreaddir(lock, 1)) && !errflag) {
-	    /* prefix and suffix are zle trickery */
-	    if (!dirs && !colonmod &&
-		((glob_pre && !strpfx(glob_pre, fn))
-		 || (glob_suf && !strsfx(glob_suf, fn))))
-		continue;
-	    errsfound = errssofar;
-	    if (pattry(p, fn)) {
-		/* if this name matches the pattern... */
-		if (pbcwdsav == pathbufcwd &&
-		    strlen(fn) + pathpos - pathbufcwd >= PATH_MAX) {
-		    int err;
-
-		    DPUTS(pathpos == pathbufcwd,
-			  "BUG: filename longer than PATH_MAX");
-		    err = lchdir(unmeta(pathbuf + pathbufcwd), &ds, 0);
-		    if (err == -1)
-			break;
-		    if (err) {
-			zerr("current directory lost during glob");
-			break;
+
+	/* Then, if we have read permission, try to open the directory. */
+	if (access(fn, R_OK) == 0) {
+	    int dirs = !!q->next;
+	    DIR *lock = opendir(fn);
+
+	    if (lock == NULL)
+		return;
+
+	    while ((fn = zreaddir(lock, 1)) && !errflag) {
+		/* prefix and suffix are zle trickery */
+		if (!dirs && !colonmod &&
+		    ((glob_pre && !strpfx(glob_pre, fn))
+		     || (glob_suf && !strsfx(glob_suf, fn))))
+		    continue;
+		errsfound = errssofar;
+		if (pattry(p, fn)) {
+		    /* if this name matches the pattern... */
+		    if (pbcwdsav == pathbufcwd &&
+			strlen(fn) + pathpos - pathbufcwd >= PATH_MAX) {
+			int err;
+
+			DPUTS(pathpos == pathbufcwd,
+			      "BUG: filename longer than PATH_MAX");
+			err = lchdir(unmeta(pathbuf + pathbufcwd), &ds, 0);
+			if (err == -1)
+			    break;
+			if (err) {
+			    zerr("current directory lost during glob");
+			    break;
+			}
+			pathbufcwd = pathpos;
 		    }
-		    pathbufcwd = pathpos;
-		}
-		if (dirs) {
-		    int l;
+		    if (dirs) {
+			int l;

-		    /*
-		     * If not the last component in the path:
-		     *
-		     * If we made an approximation in the new path segment,
-		     * then it is possible we made too many errors.  For
-		     * example, (ab)#(cb)# will match the directory abcb
-		     * with one error if allowed to, even though it can
-		     * match with none.  This will stop later parts of the
-		     * path matching, so we need to check by reducing the
-		     * maximum number of errors and seeing if the directory
-		     * still matches.  Luckily, this is not a terribly
-		     * common case, since complex patterns typically occur
-		     * in the last part of the path which is not affected
-		     * by this problem.
-		     */
-		    if (errsfound > errssofar) {
-			forceerrs = errsfound - 1;
-			while (forceerrs >= errssofar) {
-			    errsfound = errssofar;
-			    if (!pattry(p, fn))
-				break;
+			/*
+			 * If not the last component in the path:
+			 *
+			 * If we made an approximation in the new path segment,
+			 * then it is possible we made too many errors.  For
+			 * example, (ab)#(cb)# will match the directory abcb
+			 * with one error if allowed to, even though it can
+			 * match with none.  This will stop later parts of the
+			 * path matching, so we need to check by reducing the
+			 * maximum number of errors and seeing if the directory
+			 * still matches.  Luckily, this is not a terribly
+			 * common case, since complex patterns typically occur
+			 * in the last part of the path which is not affected
+			 * by this problem.
+			 */
+			if (errsfound > errssofar) {
 			    forceerrs = errsfound - 1;
+			    while (forceerrs >= errssofar) {
+				errsfound = errssofar;
+				if (!pattry(p, fn))
+				    break;
+				forceerrs = errsfound - 1;
+			    }
+			    errsfound = forceerrs + 1;
+			    forceerrs = -1;
 			}
-			errsfound = forceerrs + 1;
-			forceerrs = -1;
-		    }
-		    if (closure) {
-			/* if matching multiple directories */
-			struct stat buf;
-
-			if (statfullpath(fn, &buf, !q->follow)) {
-			    if (errno != ENOENT && errno != EINTR &&
-				errno != ENOTDIR && !errflag) {
-				zwarn("%e: %s", errno, fn);
+			if (closure) {
+			    /* if matching multiple directories */
+			    struct stat buf;
+
+			    if (statfullpath(fn, &buf, !q->follow)) {
+				if (errno != ENOENT && errno != EINTR &&
+				    errno != ENOTDIR && !errflag) {
+				    zwarn("%e: %s", errno, fn);
+				}
+				continue;
 			    }
-			    continue;
+			    if (!S_ISDIR(buf.st_mode))
+				continue;
+			}
+			l = strlen(fn) + 1;
+			subdirs = hrealloc(subdirs, subdirlen, subdirlen + l
+					   + sizeof(int));
+			strcpy(subdirs + subdirlen, fn);
+			subdirlen += l;
+			/* store the count of errors made so far, too */
+			memcpy(subdirs + subdirlen, (char *)&errsfound,
+			       sizeof(int));
+			subdirlen += sizeof(int);
+		    } else {
+			/* if the last filename component, just add it */
+			insert(fn, 1);
+			if (shortcircuit && shortcircuit == matchct) {
+			    closedir(lock);
+			    return;
 			}
-			if (!S_ISDIR(buf.st_mode))
-			    continue;
-		    }
-		    l = strlen(fn) + 1;
-		    subdirs = hrealloc(subdirs, subdirlen, subdirlen + l
-				       + sizeof(int));
-		    strcpy(subdirs + subdirlen, fn);
-		    subdirlen += l;
-		    /* store the count of errors made so far, too */
-		    memcpy(subdirs + subdirlen, (char *)&errsfound,
-			   sizeof(int));
-		    subdirlen += sizeof(int);
-		} else {
-		    /* if the last filename component, just add it */
-		    insert(fn, 1);
-		    if (shortcircuit && shortcircuit == matchct) {
-			closedir(lock);
-			return;
 		    }
 		}
 	    }
+	    closedir(lock);
 	}
-	closedir(lock);
 	if (subdirs) {
 	    int oppos = pathpos;

-- 
2.30.0