archive_write_disk_posix: check_symlinks_fsobj() without chdir()

only on platforms with openat(), fstatat() and unlinkat() support

1 files changed, 102 insertions, 14 deletions

diff --git a/libarchive/archive_write_disk_posix.c b/libarchive/archive_write_disk_posix.c
index 0583fbd1..02745d17 100644
--- a/libarchive/archive_write_disk_posix.c
+++ b/libarchive/archive_write_disk_posix.c
@@ -165,6 +165,10 @@ __FBSDID("$FreeBSD$");
 #define O_NOFOLLOW 0
 #endif
 
+#ifndef AT_FDCWD
+#define AT_FDCWD -100
+#endif
+
 struct fixup_entry {
 	struct fixup_entry	*next;
 	struct archive_acl	 acl;
@@ -349,6 +353,8 @@ struct archive_write_disk {
 
 #define HFS_BLOCKS(s)	((s) >> 12)
 
+
+static int	la_opendirat(int, const char *);
 static void	fsobj_error(int *, struct archive_string *, int, const char *,
 		    const char *);
 static int	check_symlinks_fsobj(char *, int *, struct archive_string *,
@@ -402,6 +408,37 @@ static ssize_t	_archive_write_disk_data_block(struct archive *, const void *,
 		    size_t, int64_t);
 
 static int
+la_opendirat(int fd, const char *path) {
+	const int flags = O_CLOEXEC
+#if defined(O_BINARY)
+	    | O_BINARY
+#endif
+#if defined(O_DIRECTORY)
+	    | O_DIRECTORY
+#endif
+#if defined(O_PATH)
+	    | O_PATH
+#elif defined(O_SEARCH)
+	    | O_SEARCH
+#elif defined(O_EXEC)
+	    | O_EXEC
+#else
+	    | O_RDONLY
+#endif
+	    ;
+
+#if !defined(HAVE_OPENAT)
+	if (fd != AT_FDCWD) {
+		errno = ENOTSUP;
+		return (-1);
+	} else
+		return (open(fd, path, flags));
+#else
+	return (openat(fd, path, flags));
+#endif
+}
+
+static int
 lazy_stat(struct archive_write_disk *a)
 {
 	if (a->pst != NULL) {
@@ -2565,7 +2602,8 @@ static int
 check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
     int flags)
 {
-#if !defined(HAVE_LSTAT)
+#if !defined(HAVE_LSTAT) && \
+    !(defined(HAVE_OPENAT) && defined(HAVE_FSTATAT) && defined(HAVE_UNLINKAT))
 	/* Platform doesn't have lstat, so we can't look for symlinks. */
 	(void)path; /* UNUSED */
 	(void)error_number; /* UNUSED */
@@ -2580,7 +2618,10 @@ check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
 	char c;
 	int r;
 	struct stat st;
-	int restore_pwd;
+	int chdir_fd;
+#if defined(HAVE_OPENAT) && defined(HAVE_FSTATAT) && defined(HAVE_UNLINKAT)
+	int fd;
+#endif
 
 	/* Nothing to do here if name is empty */
 	if(path[0] == '\0')
@@ -2601,9 +2642,9 @@ check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
 	 *  c holds what used to be in *tail
 	 *  last is 1 if this is the last tail
 	 */
-	restore_pwd = open(".", O_RDONLY | O_BINARY | O_CLOEXEC);
-	__archive_ensure_cloexec_flag(restore_pwd);
-	if (restore_pwd < 0) {
+	chdir_fd = la_opendirat(AT_FDCWD, ".");
+	__archive_ensure_cloexec_flag(chdir_fd);
+	if (chdir_fd < 0) {
 		fsobj_error(a_eno, a_estr, errno,
 		    "Could not open ", path);
 		return (ARCHIVE_FATAL);
@@ -2636,7 +2677,11 @@ check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
 		c = tail[0];
 		tail[0] = '\0';
 		/* Check that we haven't hit a symlink. */
+#if defined(HAVE_OPENAT) && defined(HAVE_FSTATAT) && defined(HAVE_UNLINKAT)
+		r = fstatat(chdir_fd, head, &st, AT_SYMLINK_NOFOLLOW);
+#else
 		r = lstat(head, &st);
+#endif
 		if (r != 0) {
 			tail[0] = c;
 			/* We've hit a dir that doesn't exist; stop now. */
@@ -2662,7 +2707,19 @@ check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
 			}
 		} else if (S_ISDIR(st.st_mode)) {
 			if (!last) {
-				if (chdir(head) != 0) {
+#if defined(HAVE_OPENAT) && defined(HAVE_FSTATAT) && defined(HAVE_UNLINKAT)
+				fd = la_opendirat(chdir_fd, head);
+				if (fd < 0)
+					r = -1;
+				else {
+					r = 0;
+					close(chdir_fd);
+					chdir_fd = fd;
+				}
+#else
+				r = chdir(head);
+#endif
+				if (r != 0) {
 					tail[0] = c;
 					fsobj_error(a_eno, a_estr, errno,
 					    "Could not chdir ", path);
@@ -2679,7 +2736,12 @@ check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
 				 * so we can overwrite it with the
 				 * item being extracted.
 				 */
-				if (unlink(head)) {
+#if defined(HAVE_OPENAT) && defined(HAVE_FSTATAT) && defined(HAVE_UNLINKAT)
+				r = unlinkat(chdir_fd, head, 0);
+#else
+				r = unlink(head);
+#endif
+				if (r != 0) {
 					tail[0] = c;
 					fsobj_error(a_eno, a_estr, errno,
 					    "Could not remove symlink ",
@@ -2709,7 +2771,12 @@ check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
 				break;
 			} else if (flags & ARCHIVE_EXTRACT_UNLINK) {
 				/* User asked us to remove problems. */
-				if (unlink(head) != 0) {
+#if defined(HAVE_OPENAT) && defined(HAVE_FSTATAT) && defined(HAVE_UNLINKAT)
+				r = unlinkat(chdir_fd, head, 0);
+#else
+				r = unlink(head);
+#endif
+				if (r != 0) {
 					tail[0] = c;
 					fsobj_error(a_eno, a_estr, 0,
 					    "Cannot remove intervening "
@@ -2727,7 +2794,11 @@ check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
 				 * This is needed to extract hardlinks over
 				 * symlinks.
 				 */
+#if defined(HAVE_OPENAT) && defined(HAVE_FSTATAT) && defined(HAVE_UNLINKAT)
+				r = fstatat(chdir_fd, head, &st, 0);
+#else
 				r = la_stat(head, &st);
+#endif
 				if (r != 0) {
 					tail[0] = c;
 					if (errno == ENOENT) {
@@ -2740,7 +2811,19 @@ check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
 						break;
 					}
 				} else if (S_ISDIR(st.st_mode)) {
-					if (chdir(head) != 0) {
+#if defined(HAVE_OPENAT) && defined(HAVE_FSTATAT) && defined(HAVE_UNLINKAT)
+					fd = la_opendirat(chdir_fd, head);
+					if (fd < 0)
+						r = -1;
+					else {
+						r = 0;
+						close(chdir_fd);
+						chdir_fd = fd;
+					}
+#else
+					r = chdir(head);
+#endif
+					if (r != 0) {
 						tail[0] = c;
 						fsobj_error(a_eno, a_estr,
 						    errno,
@@ -2776,16 +2859,21 @@ check_symlinks_fsobj(char *path, int *a_eno, struct archive_string *a_estr,
 	}
 	/* Catches loop exits via break */
 	tail[0] = c;
-#ifdef HAVE_FCHDIR
+#if defined(HAVE_OPENAT) && defined(HAVE_FSTATAT) && defined(HAVE_UNLINKAT)
+	/* If we operate with openat(), fstatat() and unlinkat() there was
+	 * no chdir(), so just close the fd */
+	if (chdir_fd >= 0)
+		close(chdir_fd);
+#elif HAVE_FCHDIR
 	/* If we changed directory above, restore it here. */
-	if (restore_pwd >= 0) {
-		r = fchdir(restore_pwd);
+	if (chdir_fd >= 0) {
+		r = fchdir(chdir_fd);
 		if (r != 0) {
 			fsobj_error(a_eno, a_estr, errno,
 			    "chdir() failure", "");
 		}
-		close(restore_pwd);
-		restore_pwd = -1;
+		close(chdir_fd);
+		chdir_fd = -1;
 		if (r != 0) {
 			res = (ARCHIVE_FATAL);
 		}