Add --strip-components option, per bin/77666.

Thanks to: Sangwoo Shim

usr.bin/tar/Makefile

@@ -6,7 +6,7 @@
 #
 
 PROG=	bsdtar
-VERSION=	1.01.020
+VERSION=	1.01.021
 SRCS=	bsdtar.c matching.c read.c util.c write.c
 WARNS?=	6
 DPADD=	${LIBARCHIVE} ${LIBBZ2} ${LIBZ}

usr.bin/tar/bsdtar.1

@@ -302,6 +302,12 @@ If
 is being run by root, the default is to restore the owner unless the
 .Fl o
 option is also specified.
+.It Fl -strip-components Ar count ( Fl W Cm strip-components Ns = Ns Ar count )
+(x and t mode only)
+Remove the specified number of leading path elements.
+Pathnames with fewer elements will be silently skipped.
+Note that the pathname is edited after checking inclusion/exclusion patterns
+but before security checks.
 .It Fl T Ar filename
 In x or t mode,
 .Nm

usr.bin/tar/bsdtar.c

@@ -115,7 +115,8 @@ static const char *tar_opts = "+Bb:C:cF:f:HhI:jkLlmnOoPprtT:UuvW:wX:xyZz";
 #define	OPTION_NODUMP 18
 #define	OPTION_NO_SAME_PERMISSIONS 21
 #define	OPTION_NULL 24
-#define	OPTION_ONE_FILE_SYSTEM 27
+#define	OPTION_ONE_FILE_SYSTEM 25
+#define	OPTION_STRIP_COMPONENTS 27
 #define	OPTION_TOTALS 28
 #define	OPTION_VERSION 30
 
@@ -161,6 +162,7 @@ static const struct option tar_longopts[] = {
 	{ "preserve-permissions", no_argument,     NULL, 'p' },
 	{ "read-full-blocks",	no_argument,	   NULL, 'B' },
 	{ "same-permissions",   no_argument,       NULL, 'p' },
+	{ "strip-components",	required_argument, NULL, OPTION_STRIP_COMPONENTS },
 	{ "to-stdout",          no_argument,       NULL, 'O' },
 	{ "totals",		no_argument,       NULL, OPTION_TOTALS },
 	{ "unlink",		no_argument,       NULL, 'U' },
@@ -369,6 +371,9 @@ main(int argc, char **argv)
 		case 'r': /* SUSv2 */
 			set_mode(bsdtar, opt);
 			break;
+		case OPTION_STRIP_COMPONENTS:
+			bsdtar->strip_components = atoi(optarg);
+			break;
 		case 'T': /* GNU tar */
 			bsdtar->names_from_file = optarg;
 			break;

usr.bin/tar/bsdtar.h

@@ -51,6 +51,7 @@ struct bsdtar {
 	int		  bytes_per_block; /* -b block_size */
 	int		  verbose;   /* -v */
 	int		  extract_flags; /* Flags for extract operation */
+	int		  strip_components; /* Remove this many leading dirs */
 	char		  mode; /* Program mode: 'c', 't', 'r', 'u', 'x' */
 	char		  symlink_mode; /* H or L, per BSD conventions */
 	char		  create_compression; /* j, y, or z */

usr.bin/tar/read.c

@@ -46,6 +46,7 @@ __FBSDID("$FreeBSD$");
 #include "bsdtar.h"
 
 static void	cleanup_security(struct bsdtar *);
+static int	edit_pathname(struct bsdtar *, struct archive_entry *);
 static void	list_item_verbose(struct bsdtar *, FILE *,
 		    struct archive_entry *);
 static void	read_archive(struct bsdtar *bsdtar, char mode);
@@ -115,9 +116,29 @@ read_archive(struct bsdtar *bsdtar, char mode)
 			continue;
 		}
 
+		/*
+		 * Note that exclusions are checked before pathname
+		 * rewrites are handled.  This gives more control over
+		 * exclusions, since rewrites always lose information.
+		 * (For example, consider a rewrite s/foo[0-9]/foo/.
+		 * If we check exclusions after the rewrite, there
+		 * would be no way to exclude foo1/bar while allowing
+		 * foo2/bar.)
+		 */
 		if (excluded(bsdtar, archive_entry_pathname(entry)))
 			continue;
 
+		/*
+		 * Modify the pathname as requested by the user.  We
+		 * do this for -t as well to give users a way to
+		 * preview the effects of their rewrites.  We also do
+		 * this before extraction security checks (including
+		 * leading '/' removal).  Note that some rewrite
+		 * failures prevent extraction.
+		 */
+		if (edit_pathname(bsdtar, entry))
+			continue;
+
 		if (mode == 't') {
 			/* Perversely, gtar uses -O to mean "send to stderr"
 			 * when used with -t. */
@@ -295,6 +316,43 @@ list_item_verbose(struct bsdtar *bsdtar, FILE *out, struct archive_entry *entry)
 		safe_fprintf(out, " -> %s", archive_entry_symlink(entry));
 }
 
+/*
+ * Handle --strip-components and any future path-rewriting options.
+ * Returns non-zero if the pathname should not be extracted.
+ */
+static int
+edit_pathname(struct bsdtar *bsdtar, struct archive_entry *entry)
+{
+	/* Strip leading dir names as per --strip-components option. */
+	if (bsdtar->strip_components > 0) {
+		int r = bsdtar->strip_components;
+		const char *name = archive_entry_pathname(entry);
+		const char *p = name;
+		char *q;
+
+		while (r > 0) {
+			switch (*p++) {
+			case '/':
+				r--;
+				name = p;
+				break;
+			case '\0':
+				/* Path is too short, skip it. */
+				return (1);
+			}
+		}
+		/* Safely replace name in archive_entry. */
+		q = strdup(name);
+		archive_entry_copy_pathname(entry, q);
+		free(q);
+	}
+
+	return (0);
+}
+
+/*
+ * Structure for storing path of last successful security check.
+ */
 struct security {
 	char	*path;
 	size_t	 path_size;