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>

diff --git a/archival/libarchive/Kbuild.src b/archival/libarchive/Kbuild.src
index 942e755b902627d631bbf97c2a49b9d591be7d37..e1a8a75291763daedb9c30986ac1346c35b6b579 100644 (file)
--- a/archival/libarchive/Kbuild.src
+++ b/archival/libarchive/Kbuild.src
@@ -11,6 +11,8 @@ COMMON_FILES:= \
        data_skip.o \
        data_extract_all.o \
        data_extract_to_stdout.o \
+\
+       unsafe_symlink_target.o \
 \
        filter_accept_all.o \
        filter_accept_list.o \

diff --git a/archival/libarchive/data_extract_all.c b/archival/libarchive/data_extract_all.c
index 1ce927c2f1f5cf6c62eff0681c1aa0b227efff64..e658444e03c8fd0d7be418690df0254f77b2050d 100644 (file)
--- 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 (file)
index 0000000..441ba8b
--- /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;
+       }
+}

diff --git a/archival/tar.c b/archival/tar.c
index 73c14ca8136e001872ecebfa6ee9d28d493ef22d..9a5bcc7febc635591bdd4358a92b65d068de6c22 100644 (file)
--- a/archival/tar.c
+++ b/archival/tar.c
@@ -278,23 +278,6 @@ static void chksum_and_xwrite(int fd, struct tar_header_t* hp)
        xwrite(fd, hp, sizeof(*hp));
 }
 
-static void replace_symlink_placeholders(llist_t *list)
-{
-       while (list) {
-               char *target;
-
-               target = list->data + strlen(list->data) + 1;
-               if (symlink(target, list->data)) {
-                       /* shared message */
-                       bb_error_msg_and_die("can't create %slink '%s' to '%s'",
-                               "sym",
-                               list->data, target
-                       );
-               }
-               list = list->link;
-       }
-}
-
 #if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
 static void writeLongname(int fd, int type, const char *name, int dir)
 {
@@ -1255,8 +1238,6 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
        while (get_header_tar(tar_handle) == EXIT_SUCCESS)
                bb_got_signal = EXIT_SUCCESS; /* saw at least one header, good */
 
-       replace_symlink_placeholders(tar_handle->symlink_placeholders);
-
        /* Check that every file that should have been extracted was */
        while (tar_handle->accept) {
                if (!find_list_entry(tar_handle->reject, tar_handle->accept->data)

diff --git a/archival/unzip.c b/archival/unzip.c
index 8ed9ae7d5ed28a7617a4b33eec6c4553b21882f6..60416606397ed72fbb645db4f9dc16394b201f97 100644 (file)
--- a/archival/unzip.c
+++ b/archival/unzip.c
@@ -368,9 +368,15 @@ static void unzip_extract_symlink(zip_header_t *zip, const char *dst_fn)
                target[xstate.mem_output_size] = '\0';
 #endif
        }
+       if (!unsafe_symlink_target(target)) {
 //TODO: libbb candidate
-       if (symlink(target, dst_fn))
-               bb_perror_msg_and_die("can't create symlink '%s'", dst_fn);
+               if (symlink(target, dst_fn)) {
+                       /* shared message */
+                       bb_perror_msg_and_die("can't create %slink '%s' to '%s'",
+                               "sym", dst_fn, target
+                       );
+               }
+       }
        free(target);
 }
 #endif

diff --git a/coreutils/link.c b/coreutils/link.c
index 81808b778c65bc91b6442700af5ceca4a8b1ca8d..d8d583b7b79bd4ef64e452df11643e146c4bfac2 100644 (file)
--- a/coreutils/link.c
+++ b/coreutils/link.c
@@ -31,9 +31,8 @@ int link_main(int argc UNUSED_PARAM, char **argv)
        argv += optind;
        if (link(argv[0], argv[1]) != 0) {
                /* shared message */
-               bb_perror_msg_and_die("can't create %slink "
-                                       "'%s' to '%s'", "hard",
-                                       argv[1], argv[0]
+               bb_perror_msg_and_die("can't create %slink '%s' to '%s'",
+                       "hard", argv[1], argv[0]
                );
        }
        return EXIT_SUCCESS;

diff --git a/include/bb_archive.h b/include/bb_archive.h
index d3762415fa4cd5888c57481c868b2880943c3c75..d3a02cf1802ab478eb2888b416dcb8fa8c5ffe0b 100644 (file)
--- a/include/bb_archive.h
+++ b/include/bb_archive.h
@@ -64,9 +64,6 @@ typedef struct archive_handle_t {
        /* Currently processed file's header */
        file_header_t *file_header;
 
-       /* List of symlink placeholders */
-       llist_t *symlink_placeholders;
-
        /* Process the header component, e.g. tar -t */
        void FAST_FUNC (*action_header)(const file_header_t *);
 
@@ -200,6 +197,7 @@ void seek_by_jump(int fd, off_t amount) FAST_FUNC;
 void seek_by_read(int fd, off_t amount) FAST_FUNC;
 
 const char *strip_unsafe_prefix(const char *str) FAST_FUNC;
+int unsafe_symlink_target(const char *target) FAST_FUNC;
 
 void data_align(archive_handle_t *archive_handle, unsigned boundary) FAST_FUNC;
 const llist_t *find_list_entry(const llist_t *list, const char *filename) FAST_FUNC;

diff --git a/libbb/copy_file.c b/libbb/copy_file.c
index 23c0f8320b86f19f5d1a478368843340bd1bf51b..be90066311fbb34c48e8c0def9d206db9c262068 100644 (file)
--- a/libbb/copy_file.c
+++ b/libbb/copy_file.c
@@ -371,7 +371,10 @@ int FAST_FUNC copy_file(const char *source, const char *dest, int flags)
                        int r = symlink(lpath, dest);
                        free(lpath);
                        if (r < 0) {
-                               bb_perror_msg("can't create symlink '%s'", dest);
+                               /* shared message */
+                               bb_perror_msg("can't create %slink '%s' to '%s'",
+                                       "sym", dest, lpath
+                               );
                                return -1;
                        }
                        if (flags & FILEUTILS_PRESERVE_STATUS)

diff --git a/testsuite/tar.tests b/testsuite/tar.tests
index 1675b07b14e0f761bc3cb8e7e5c15fe1959e8291..b7cd74ca5da75f3f154a7a675d3eb9026069d405 100755 (executable)
--- a/testsuite/tar.tests
+++ b/testsuite/tar.tests
@@ -279,7 +279,7 @@ optional UUDECODE FEATURE_TAR_AUTODETECT FEATURE_SEAMLESS_BZ2
 testing "tar does not extract into symlinks" "\
 >>/tmp/passwd && uudecode -o input && tar xf input 2>&1 && rm passwd; cat /tmp/passwd; echo \$?
 " "\
-tar: can't create symlink 'passwd' to '/tmp/passwd'
+tar: skipping unsafe symlink to '/tmp/passwd' in archive, set EXTRACT_UNSAFE_SYMLINKS=1 to extract
 0
 " \
 "" "\
@@ -299,7 +299,7 @@ optional UUDECODE FEATURE_TAR_AUTODETECT FEATURE_SEAMLESS_BZ2
 testing "tar -k does not extract into symlinks" "\
 >>/tmp/passwd && uudecode -o input && tar xf input -k 2>&1 && rm passwd; cat /tmp/passwd; echo \$?
 " "\
-tar: can't create symlink 'passwd' to '/tmp/passwd'
+tar: skipping unsafe symlink to '/tmp/passwd' in archive, set EXTRACT_UNSAFE_SYMLINKS=1 to extract
 0
 " \
 "" "\
@@ -324,11 +324,11 @@ rm -rf etc usr
 ' "\
 etc/ssl/certs/3b2716e5.0
 etc/ssl/certs/EBG_Elektronik_Sertifika_Hizmet_Sağlayıcısı.pem
+tar: skipping unsafe symlink to '/usr/share/ca-certificates/mozilla/EBG_Elektronik_Sertifika_Hizmet_Sağlayıcısı.crt' in archive, set EXTRACT_UNSAFE_SYMLINKS=1 to extract
 etc/ssl/certs/f80cc7f6.0
 usr/share/ca-certificates/mozilla/EBG_Elektronik_Sertifika_Hizmet_Sağlayıcısı.crt
 0
 etc/ssl/certs/3b2716e5.0 -> EBG_Elektronik_Sertifika_Hizmet_Sağlayıcısı.pem
-etc/ssl/certs/EBG_Elektronik_Sertifika_Hizmet_Sağlayıcısı.pem -> /usr/share/ca-certificates/mozilla/EBG_Elektronik_Sertifika_Hizmet_Sağlayıcısı.crt
 etc/ssl/certs/f80cc7f6.0 -> EBG_Elektronik_Sertifika_Hizmet_Sağlayıcısı.pem
 " \
 "" ""
@@ -346,9 +346,9 @@ ls symlink/bb_test_evilfile
 ' "\
 anything.txt
 symlink
+tar: skipping unsafe symlink to '/tmp' in archive, set EXTRACT_UNSAFE_SYMLINKS=1 to extract
 symlink/bb_test_evilfile
-tar: can't create symlink 'symlink' to '/tmp'
-1
+0
 ls: /tmp/bb_test_evilfile: No such file or directory
 ls: bb_test_evilfile: No such file or directory
 symlink/bb_test_evilfile