linkup

commit 02748101b3fb3a8a8aaaacc5c4e1e62dd0ea45fc
parent 47bfb593e8f3d808340954ffe5352d21b5f76307
Author: Louis Burda <quent.burda@gmail.com>
Date:   Sat, 22 Oct 2022 15:11:52 +0200

Fix resolving of dangling symbolic links

Diffstat:
M
linkup.c
 | 
94
+++++++++++++++++++++++++++++++++++++++++++++++++++++--------------------------

1 file changed, 63 insertions(+), 31 deletions(-)
diff --git a/linkup.c b/linkup.c
@@ -27,37 +27,66 @@ exists(int dirfd, const char *path)
 }
 
 void
-remove_all(int pfd, const char *path)
+normalize(const char *src, char *dst)
 {
-	struct dirent *ent;
-	struct stat attr;
-	DIR *dir;
-	int fd;
-
-	if (fstatat(pfd, path, &attr, AT_SYMLINK_NOFOLLOW) < 0) {
-		if (errno == ENOENT) return;
-		err(1, "fstatat");
+	const char *sep, *tok;
+	char *end;
+	int len;
+
+	/* only for absolute paths */
+
+	end = dst;
+	tok = src;
+	*end = '\0';
+	while (1) {
+		sep = strchr(tok, '/');
+		len = sep ? sep - tok : strlen(tok);
+		if (!len || !strncmp(tok, ".", len))
+			goto next;
+		if (!strncmp(tok, "..", len)) {
+			end = strrchr(dst, '/');
+			if (!end) end = dst;
+			*end = '\0';
+		} else {
+			*end++ = '/';
+			strncpy(end, tok, len);
+			end += len;
+			*end = '\0';
+		}
+next:
+		tok = sep + 1;
+		if (!sep) break;
 	}
+}
 
-	if ((attr.st_mode & S_IFMT) == S_IFDIR) {
-		fd = openat(pfd, path, 0);
-		dir = fdopendir(fd);
-		if (!dir) err(1, "opendir");
-		while ((ent = readdir(dir)))
-			remove_all(fd, ent->d_name);
-		closedir(dir);
+void
+realparent(int dirfd, const char *dirpath, const char *file, char *parent)
+{
+	char tmpbuf[PATH_MAX];
+	char *sep;
+
+	if (readlinkat(dirfd, file, tmpbuf, PATH_MAX) < 0)
+		err(1, "readlink");
+
+	if (tmpbuf[0] != '/') { /* relative path */
+		strncpy(parent, tmpbuf, PATH_MAX);
+		snprintf(tmpbuf, PATH_MAX, "%s/%s", dirpath, parent);
 	}
 
-	unlinkat(pfd, path, AT_REMOVEDIR);
+	normalize(tmpbuf, parent);
+	if ((sep = strrchr(parent, '/')))
+		*sep = '\0';
 }
 
 void
 do_install(const char *spath, const char *dpath)
 {
 	char spbuf[PATH_MAX], dpbuf[PATH_MAX];
+	char tmpbuf[PATH_MAX];
 	struct dirent *ent;
 	struct stat attr;
 	DIR *sdir, *ddir;
+	char *sep;
 	int i;
 
 	sdir = opendir(spath);
@@ -80,17 +109,19 @@ do_install(const char *spath, const char *dpath)
 		if (!strcmp(ent->d_name, ".."))
 			continue;
 
+		snprintf(spbuf, PATH_MAX, "%s/%s", spath, ent->d_name);
+		snprintf(dpbuf, PATH_MAX, "%s/%s", dpath, ent->d_name);
+
 		/* ensure link destination does not exist */
 		if (!fstatat(dirfd(ddir), ent->d_name,
 				&attr, AT_SYMLINK_NOFOLLOW)) {
 			if ((attr.st_mode & S_IFMT) != S_IFLNK && !force)
 				errx(1, "dst %s already exists\n", ent->d_name);
-			remove_all(dirfd(ddir), ent->d_name);
+			if (remove(dpbuf))
+				err(1, "remove dst %s", ent->d_name);
 		}
 
 		/* create link */
-		snprintf(spbuf, PATH_MAX, "%s/%s", spath, ent->d_name);
-		snprintf(dpbuf, PATH_MAX, "%s/%s", dpath, ent->d_name);
 		if (symlink(spbuf, dpbuf) < 0)
 			err(1, "link");
 	}
@@ -99,12 +130,13 @@ do_install(const char *spath, const char *dpath)
 	while ((ent = readdir(ddir))) {
 		if (ent->d_type != DT_LNK)
 			continue;
-		snprintf(dpbuf, PATH_MAX, "%s/%s", dpath, ent->d_name);
-		if (readlink(dpbuf, dpbuf, PATH_MAX) < 0)
-			err(1, "readlink");
-		realpath(dpbuf, dpbuf);
-		if (strncmp(dpbuf, spath, strlen(spath)))
-			break;
+
+		/* must point into src */
+		realparent(dirfd(ddir), dpath, ent->d_name, dpbuf);
+		if (strcmp(dpbuf, spath))
+			continue;
+
+		/* with missing destination */
 		if (fstatat(dirfd(ddir), ent->d_name, &attr, 0) < 0)
 			unlinkat(dirfd(ddir), ent->d_name, 0);
 	}
@@ -118,6 +150,7 @@ do_uninstall(const char *spath, const char *dpath)
 {
 	struct dirent *ent;
 	char dpbuf[PATH_MAX];
+	char *sep;
 	DIR *ddir;
 
 	ddir = opendir(dpath);
@@ -126,11 +159,10 @@ do_uninstall(const char *spath, const char *dpath)
 	while ((ent = readdir(ddir))) {
 		if (ent->d_type != DT_LNK)
 			continue;
-		snprintf(dpbuf, PATH_MAX, "%s/%s", dpath, ent->d_name);
-		if (readlink(dpbuf, dpbuf, PATH_MAX) < 0)
-			err(1, "readlink");
-		realpath(dpbuf, dpbuf);
-		if (!strncmp(dpbuf, spath, strlen(spath)))
+
+		realparent(dirfd(ddir), dpath, ent->d_name, dpbuf);
+
+		if (!strcmp(dpbuf, spath))
 			unlinkat(dirfd(ddir), ent->d_name, 0);
 	}