Issues with hardlinks in newc-format files prompted me to

write a new test to exercise the hardlink strategies used
by different archive formats (tar, old cpio, new cpio).
This uncovered two problems, both fixed by this commit:

1) Enforce file size when writing files to disk.

2) When restoring hardlink entries, if they have data associated, go
   ahead and open the file so we can write the data.

In particular, this fixes bsdtar/bsdcpio extraction of new cpio
formats where the "original" is empty and the subsequent "hardlink"
entry actually carries the data.  It also provides correct behavior
for old cpio archives where hardlinked entries have their bodies
stored multiple times in the archive; the last body should always be
the one that ends up in the final file.  The new pax format also
permits (but does not require) hardlinks to carry file data; again,
the last contents should always win.

Note that with any of these, a size of zero on a hardlink simply means
that the hardlink carries no data; it does not mean that the file has
zero size.  A non-zero size on a hardlink does provide the file size.

Thanks to: John Baldwin, for reminding me about this long-standing bug
    and sending me a simple example archive that prompted this test case

1 files changed, 32 insertions, 6 deletions

diff --git a/lib/libarchive/archive_write_disk.c b/lib/libarchive/archive_write_disk.c
index 8b42811..f55eaf0 100644
--- a/lib/libarchive/archive_write_disk.c
+++ b/lib/libarchive/archive_write_disk.c
@@ -171,6 +171,8 @@ struct archive_write_disk {
 	int			 fd;
 	/* Current offset for writing data to the file. */
 	off_t			 offset;
+	/* Maximum size of file. */
+	off_t			 filesize;
 	/* Dir we were in before this restore; only for deep paths. */
 	int			 restore_pwd;
 	/* Mode we should use for this entry; affected by _PERM and umask. */
@@ -302,6 +304,7 @@ _archive_write_header(struct archive *_a, struct archive_entry *entry)
 	a->offset = 0;
 	a->uid = a->user_uid;
 	a->mode = archive_entry_mode(a->entry);
+	a->filesize = archive_entry_size(a->entry);
 	archive_strcpy(&(a->_name_data), archive_entry_pathname(a->entry));
 	a->name = a->_name_data.s;
 	archive_clear_error(&a->archive);
@@ -425,8 +428,10 @@ _archive_write_header(struct archive *_a, struct archive_entry *entry)
 	 * If it's not open, tell our client not to try writing.
 	 * In particular, dirs, links, etc, don't get written to.
 	 */
-	if (a->fd < 0)
+	if (a->fd < 0) {
 		archive_entry_set_size(entry, 0);
+		a->filesize = 0;
+	}
 done:
 	/* Restore the user's umask before returning. */
 	umask(a->user_umask);
@@ -451,6 +456,7 @@ _archive_write_data_block(struct archive *_a,
 {
 	struct archive_write_disk *a = (struct archive_write_disk *)_a;
 	ssize_t bytes_written = 0;
+	int r = ARCHIVE_OK;
 
 	__archive_check_magic(&a->archive, ARCHIVE_WRITE_DISK_MAGIC,
 	    ARCHIVE_STATE_DATA, "archive_write_disk_block");
@@ -470,7 +476,13 @@ _archive_write_data_block(struct archive *_a,
 	}
 
 	/* Write the data. */
-	while (size > 0) {
+	while (size > 0 && a->offset < a->filesize) {
+		if (a->offset + size > a->filesize) {
+			size = a->filesize - a->offset;
+			archive_set_error(&a->archive, errno,
+			    "Write request too large");
+			r = ARCHIVE_WARN;
+		}
 		bytes_written = write(a->fd, buff, size);
 		if (bytes_written < 0) {
 			archive_set_error(&a->archive, errno, "Write failed");
@@ -479,13 +491,14 @@ _archive_write_data_block(struct archive *_a,
 		size -= bytes_written;
 		a->offset += bytes_written;
 	}
-	return (ARCHIVE_OK);
+	return (r);
 }
 
 static ssize_t
 _archive_write_data(struct archive *_a, const void *buff, size_t size)
 {
 	struct archive_write_disk *a = (struct archive_write_disk *)_a;
+	off_t offset;
 	int r;
 
 	__archive_check_magic(&a->archive, ARCHIVE_WRITE_DISK_MAGIC,
@@ -493,10 +506,11 @@ _archive_write_data(struct archive *_a, const void *buff, size_t size)
 	if (a->fd < 0)
 		return (ARCHIVE_OK);
 
+	offset = a->offset;
 	r = _archive_write_data_block(_a, buff, size, a->offset);
 	if (r < ARCHIVE_OK)
 		return (r);
-	return (size);
+	return (a->offset - offset);
 }
 
 static int
@@ -829,8 +843,20 @@ create_filesystem_object(struct archive_write_disk *a)
 	/* We identify hard/symlinks according to the link names. */
 	/* Since link(2) and symlink(2) don't handle modes, we're done here. */
 	linkname = archive_entry_hardlink(a->entry);
-	if (linkname != NULL)
-		return link(linkname, a->name) ? errno : 0;
+	if (linkname != NULL) {
+		r = link(linkname, a->name) ? errno : 0;
+		/*
+		 * New cpio and pax formats allow hardlink entries
+		 * to carry data, so we may have to open the file
+		 * for hardlink entries.
+		 */
+		if (r == 0 && a->filesize > 0) {
+			a->fd = open(a->name, O_WRONLY | O_TRUNC);
+			if (a->fd < 0)
+				r = errno;
+		}
+		return (r);
+	}
 	linkname = archive_entry_symlink(a->entry);
 	if (linkname != NULL)
 		return symlink(linkname, a->name) ? errno : 0;