[PATCH v2]: write SELinux contexts when extracting a tar file

J. Tang tang at jtang.org
Tue Mar 16 14:58:56 UTC 2010


Here is a second iteration of the patch to enhanch tar, incorporating
suggestions be Denys.  It is baselined against the most recent commit
to origin/master.

Signed-off-by: Jason Tang <tang at jtang.org>

---
 archival/Config.in                       |    8 +++
 archival/libunarchive/data_extract_all.c |    4 +
 archival/libunarchive/get_header_tar.c   |  101 +++++++++++++++++++++++++++++-
 3 files changed, 111 insertions(+), 2 deletions(-)

diff --git a/archival/Config.in b/archival/Config.in
index c99896b..deacc28 100644
--- a/archival/Config.in
+++ b/archival/Config.in
@@ -289,6 +289,14 @@ config FEATURE_TAR_NOPRESERVE_TIME
 	  With this option busybox supports GNU tar -m
 	  (do not preserve time) option.
 
+config FEATURE_TAR_SELINUX
+	bool "Support for extracting SELinux labels"
+	default n
+	depends on TAR && SELINUX
+	help
+	  With this option busybox supports restoring SELinux labels
+	  when extracting files from tar archives.
+
 config UNCOMPRESS
 	bool "uncompress"
 	default n
diff --git a/archival/libunarchive/data_extract_all.c b/archival/libunarchive/data_extract_all.c
index 58b0533..57c5ec4 100644
--- a/archival/libunarchive/data_extract_all.c
+++ b/archival/libunarchive/data_extract_all.c
@@ -158,4 +158,8 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
 			utimes(file_header->name, t);
 		}
 	}
+#if ENABLE_FEATURE_TAR_SELINUX
+	/* always reset the context after creating an entry */
+	(void) setfscreatecon(NULL);
+#endif
 }
diff --git a/archival/libunarchive/get_header_tar.c b/archival/libunarchive/get_header_tar.c
index d5b86ff..914f145 100644
--- a/archival/libunarchive/get_header_tar.c
+++ b/archival/libunarchive/get_header_tar.c
@@ -103,6 +103,92 @@ static unsigned long long getOctal(char *str, int len)
 }
 #define GET_OCTAL(a) getOctal((a), sizeof(a))
 
+#if ENABLE_FEATURE_TAR_SELINUX
+/* Scan a PAX extended header for SELinux contexts, via
+ * "RHT.security.selinux" keyword.  This is the same vendor specific
+ * keyword used by Red Hat's patched version of tar.
+ */
+#define SELINUX_CONTEXT_KEYWORD "RHT.security.selinux"
+
+static void parse_extended_header(archive_handle_t *archive_handle, off_t sz)
+{
+	char *buf, *p, *next_p, *keyword, *value;
+	off_t len;
+
+	/* prevent a malloc of 0 */
+	if (sz == 0) {
+		return;
+	}
+
+	/* forcibly add a newline at the end of the buffer, to prevent
+	   any buffer overflows */
+	p = buf = xmalloc(sz);
+	buf[sz - 1] = '\n';
+
+	xread(archive_handle->src_fd, buf, sz);
+	archive_handle->offset += sz;
+
+	do {
+		/* skip leading whitespace */
+		while (*p == ' ' || *p == '\t') {
+			p++;
+		}
+
+		/* scan for the length of the record */
+		len = bb_strtou(p, &keyword, 10);
+		/* expect errno to be EINVAL, because the character
+		   following the digits is supposed to be a space */
+		if ((errno != EINVAL) || ((p + len) > (buf + sz))) {
+			bb_error_msg("Malformed extended header: length is out of allowed range");
+			return;
+		}
+
+		next_p = p + len;
+
+		p = keyword;
+
+		/* scan for the start of the keyword and the value;
+		   they are '=' separated */
+
+		while (*p == ' ' || *p == '\t') {
+			p++;
+		}
+		keyword = p;
+
+		while (*p != '=' && *p != '\n') {
+			p++;
+		}
+		if (*p != '=') {
+			bb_error_msg("Malformed extended header: missing equal sign");
+			return;
+		}
+
+		*p = '\0';
+
+		p++;
+		value = p;
+		while (*p != '\n') {
+			p++;
+		}
+		*p = '\0';
+
+		p = next_p;
+
+		/* handle fields that are SELinux related */
+		if (strcmp(keyword, SELINUX_CONTEXT_KEYWORD) == 0) {
+			/* free old context, in case context is given
+			   multiple times */
+			if (setfscreatecon(value) < 0) {
+				bb_perror_msg("cannot set label to '%s'", value);
+			}
+		}
+
+	} while (p < buf + sz);
+
+	free(buf);
+}
+#endif
+
 void BUG_tar_header_size(void);
 char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
 {
@@ -150,7 +236,7 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
 	if (sizeof(tar) != 512)
 		BUG_tar_header_size();
 
-#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
+#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS || ENABLE_FEATURE_TAR_SELINUX
  again:
 #endif
 	/* Align header */
@@ -393,7 +479,10 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
 	case 'V':	/* Volume header */
 #endif
 	case 'g':	/* pax global header */
-	case 'x': {	/* pax extended header */
+#if !ENABLE_FEATURE_TAR_SELINUX
+	case 'x':	/* pax extended header, which is skipped */
+#endif
+	{
 		off_t sz;
 		bb_error_msg("warning: skipping header '%c'", tar.typeflag);
 		sz = (file_header->size + 511) & ~(off_t)511;
@@ -404,6 +493,14 @@ char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
 		/* return get_header_tar(archive_handle); */
 		goto again_after_align;
 	}
+#if ENABLE_FEATURE_TAR_SELINUX
+	case 'x': {	/* pax extended header */
+		/* read the rest of the extended header, and then
+		   parse its contents */
+		parse_extended_header(archive_handle, file_header->size);
+		goto again;
+#endif
+	}
 	default:
 		bb_error_msg_and_die("unknown typeflag: 0x%x", tar.typeflag);
 	}
-- 
1.6.6.1

-- 
Jason Tang  /  tang at jtang.org  /  http://www.jtang.org


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