3 files changed, 44 insertions, 34 deletions

diff --git a/lib/libarchive/archive_read.c b/lib/libarchive/archive_read.c
index c92b20c..06a4e8c 100644
--- a/lib/libarchive/archive_read.c
+++ b/lib/libarchive/archive_read.c
@@ -55,6 +55,7 @@ __FBSDID("$FreeBSD$");
 
 static int	choose_decompressor(struct archive_read *, const void*, size_t);
 static int	choose_format(struct archive_read *);
+static off_t	dummy_skip(struct archive_read *, off_t);
 
 /*
  * Allocate, initialize and return a struct archive object.
@@ -191,6 +192,13 @@ archive_read_open2(struct archive *_a, void *client_data,
 	if (e == ARCHIVE_OK)
 		a->archive.state = ARCHIVE_STATE_HEADER;
 
+	/*
+	 * If the decompressor didn't register a skip function, provide a
+	 * dummy compression-layer skip function.
+	 */
+	if (a->compression_skip == NULL)
+		a->compression_skip = dummy_skip;
+
 	return (e);
 }
 
@@ -244,6 +252,38 @@ choose_decompressor(struct archive_read *a,
 }
 
 /*
+ * Dummy skip function, for use if the compression layer doesn't provide
+ * one: This code just reads data and discards it.
+ */
+static off_t
+dummy_skip(struct archive_read * a, off_t request)
+{
+	const void * dummy_buffer;
+	ssize_t bytes_read;
+	off_t bytes_skipped;
+
+	for (bytes_skipped = 0; request > 0;) {
+		bytes_read = (a->compression_read_ahead)(a, &dummy_buffer, 1);
+		if (bytes_read < 0)
+			return (bytes_read);
+		if (bytes_read == 0) {
+			/* Premature EOF. */
+			archive_set_error(&a->archive, ARCHIVE_ERRNO_MISC,
+			    "Truncated input file (need to skip %jd bytes)",
+			    (intmax_t)request);
+			return (ARCHIVE_FATAL);
+		}
+		if (bytes_read > request)
+			bytes_read = request;
+		(a->compression_read_consume)(a, bytes_read);
+		request -= bytes_read;
+		bytes_skipped += bytes_read;
+	}
+
+	return (bytes_skipped);
+}
+
+/*
  * Read header of next entry.
  */
 int
diff --git a/lib/libarchive/archive_read_support_format_iso9660.c b/lib/libarchive/archive_read_support_format_iso9660.c
index f115b0e..c892f72 100644
--- a/lib/libarchive/archive_read_support_format_iso9660.c
+++ b/lib/libarchive/archive_read_support_format_iso9660.c
@@ -917,33 +917,13 @@ fprintf(stderr, " *** Discarding CE data.\n");
 			offset = file->offset;
 
 		/* Seek forward to the start of the entry. */
-		/* Use fast compression_skip if it's available. */
-		if (iso9660->current_position < offset
-		    && a->compression_skip != NULL) {
+		if (iso9660->current_position < offset) {
 			off_t step = offset - iso9660->current_position;
 			off_t bytes_read;
 			bytes_read = (a->compression_skip)(a, step);
-			iso9660->current_position += bytes_read;
-		}
-
-		/* Use a series of reads if compression_skip didn't
-		 * get us all the way there. */
-		while (iso9660->current_position < offset) {
-			ssize_t step = offset - iso9660->current_position;
-			ssize_t bytes_read;
-			const void *buff;
-
-			if (step > iso9660->logical_block_size)
-				step = iso9660->logical_block_size;
-			bytes_read = (a->compression_read_ahead)(a, &buff, step);
-			if (bytes_read <= 0) {
-				release_file(iso9660, file);
-				return (ARCHIVE_FATAL);
-			}
-			if (bytes_read > step)
-				bytes_read = step;
-			iso9660->current_position += bytes_read;
-			(a->compression_read_consume)(a, bytes_read);
+			if (bytes_read < 0)
+				return (bytes_read);
+			iso9660->current_position = offset;
 		}
 
 		/* We found body of file; handle it now. */
diff --git a/lib/libarchive/archive_read_support_format_tar.c b/lib/libarchive/archive_read_support_format_tar.c
index 8aa5a38..3c24733 100644
--- a/lib/libarchive/archive_read_support_format_tar.c
+++ b/lib/libarchive/archive_read_support_format_tar.c
@@ -546,18 +546,8 @@ archive_read_format_tar_skip(struct archive_read *a)
 	off_t bytes_skipped;
 	struct tar* tar;
 	struct sparse_block *p;
-	int r = ARCHIVE_OK;
-	const void *b;	/* dummy variables */
-	size_t s;
-	off_t o;
-
 
 	tar = (struct tar *)*(a->pformat_data);
-	if (a->compression_skip == NULL) {
-		while (r == ARCHIVE_OK)
-			r = archive_read_format_tar_read_data(a, &b, &s, &o);
-		return (r);
-	}
 
 	/*
 	 * Compression layer skip functions are required to either skip the