aboutsummaryrefslogtreecommitdiff
path: root/archival/libarchive
diff options
context:
space:
mode:
authorDenys Vlasenko <vda.linux@googlemail.com>2017-08-10 11:52:42 +0200
committerDenys Vlasenko <vda.linux@googlemail.com>2017-08-10 11:52:42 +0200
commitbc9bbeb2b81001e8731cd2ae501c8fccc8d87cc7 (patch)
tree72672bb0c187b93f1fba99012cf0c4e716214298 /archival/libarchive
parent0cf64c8b5d86d603903397bfce87dea5a862caec (diff)
downloadbusybox-bc9bbeb2b81001e8731cd2ae501c8fccc8d87cc7.tar.gz
libarchive: do not extract unsafe symlinks unless $EXTRACT_UNSAFE_SYMLINKS=1
function old new delta unsafe_symlink_target - 147 +147 unzip_main 2711 2732 +21 copy_file 1657 1678 +21 tar_main 999 971 -28 data_extract_all 1038 984 -54 ------------------------------------------------------------------------------ (add/remove: 2/0 grow/shrink: 2/2 up/down: 189/-82) Total: 107 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'archival/libarchive')
-rw-r--r--archival/libarchive/Kbuild.src2
-rw-r--r--archival/libarchive/data_extract_all.c37
-rw-r--r--archival/libarchive/unsafe_symlink_target.c48
3 files changed, 65 insertions, 22 deletions
diff --git a/archival/libarchive/Kbuild.src b/archival/libarchive/Kbuild.src
index 942e755b9..e1a8a7529 100644
--- a/archival/libarchive/Kbuild.src
+++ b/archival/libarchive/Kbuild.src
@@ -12,6 +12,8 @@ COMMON_FILES:= \
data_extract_all.o \
data_extract_to_stdout.o \
\
+ unsafe_symlink_target.o \
+\
filter_accept_all.o \
filter_accept_list.o \
filter_accept_reject_list.o \
diff --git a/archival/libarchive/data_extract_all.c b/archival/libarchive/data_extract_all.c
index 1ce927c2f..e658444e0 100644
--- a/archival/libarchive/data_extract_all.c
+++ b/archival/libarchive/data_extract_all.c
@@ -129,9 +129,7 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
if (res != 0 && !(archive_handle->ah_flags & ARCHIVE_EXTRACT_QUIET)) {
/* shared message */
bb_perror_msg("can't create %slink '%s' to '%s'",
- "hard",
- dst_name,
- hard_link
+ "hard", dst_name, hard_link
);
}
/* Hardlinks have no separate mode/ownership, skip chown/chmod */
@@ -181,7 +179,9 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
//TODO: what if file_header->link_target == NULL (say, corrupted tarball?)
/* To avoid a directory traversal attack via symlinks,
- * for certain link targets postpone creation of symlinks.
+ * do not restore symlinks with ".." components
+ * or symlinks starting with "/", unless a magic
+ * envvar is set.
*
* For example, consider a .tar created via:
* $ tar cvf bug.tar anything.txt
@@ -199,24 +199,17 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
*
* Untarring bug.tar would otherwise place evil.py in '/tmp'.
*/
- if (file_header->link_target[0] == '/'
- || strstr(file_header->link_target, "..")
- ) {
- llist_add_to(&archive_handle->symlink_placeholders,
- xasprintf("%s%c%s", file_header->name, '\0', file_header->link_target)
- );
- break;
- }
- res = symlink(file_header->link_target, dst_name);
- if (res != 0
- && !(archive_handle->ah_flags & ARCHIVE_EXTRACT_QUIET)
- ) {
- /* shared message */
- bb_perror_msg("can't create %slink '%s' to '%s'",
- "sym",
- dst_name,
- file_header->link_target
- );
+ if (!unsafe_symlink_target(file_header->link_target)) {
+ res = symlink(file_header->link_target, dst_name);
+ if (res != 0
+ && !(archive_handle->ah_flags & ARCHIVE_EXTRACT_QUIET)
+ ) {
+ /* shared message */
+ bb_perror_msg("can't create %slink '%s' to '%s'",
+ "sym",
+ dst_name, file_header->link_target
+ );
+ }
}
break;
case S_IFSOCK:
diff --git a/archival/libarchive/unsafe_symlink_target.c b/archival/libarchive/unsafe_symlink_target.c
new file mode 100644
index 000000000..441ba8b24
--- /dev/null
+++ b/archival/libarchive/unsafe_symlink_target.c
@@ -0,0 +1,48 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+#include "libbb.h"
+#include "bb_archive.h"
+
+int FAST_FUNC unsafe_symlink_target(const char *target)
+{
+ const char *dot;
+
+ if (target[0] == '/') {
+ const char *var;
+ unsafe:
+ var = getenv("EXTRACT_UNSAFE_SYMLINKS");
+ if (var) {
+ if (LONE_CHAR(var, '1'))
+ return 0; /* pretend it's safe */
+ return 1; /* "UNSAFE!" */
+ }
+ bb_error_msg("skipping unsafe symlink to '%s' in archive,"
+ " set %s=1 to extract",
+ target,
+ "EXTRACT_UNSAFE_SYMLINKS"
+ );
+ /* Prevent further messages */
+ setenv("EXTRACT_UNSAFE_SYMLINKS", "0", 0);
+ return 1; /* "UNSAFE!" */
+ }
+
+ dot = target;
+ for (;;) {
+ dot = strchr(dot, '.');
+ if (!dot)
+ return 0; /* safe target */
+
+ /* Is it a path component starting with ".."? */
+ if ((dot[1] == '.')
+ && (dot == target || dot[-1] == '/')
+ /* Is it exactly ".."? */
+ && (dot[2] == '/' || dot[2] == '\0')
+ ) {
+ goto unsafe;
+ }
+ /* NB: it can even be trailing ".", should only add 1 */
+ dot += 1;
+ }
+}