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bc9bbeb2b

Denys Vlasenko
Denys Vlasenko
2017-08-10
SUCCESS Duration: 142s

Subject

libarchive: do not extract unsafe symlinks unless $EXTRACT_UNSAFE_SYMLINKS=1

Binary

No binary (build failed)

Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

—

Build Log

(log yok)

Commit Diff GitHub →

archival/libarchive/Kbuild.src +2 -0archival/libarchive/data_extract_all.c +15 -22archival/libarchive/unsafe_symlink_target.c +48 -0archival/tar.c +0 -19archival/unzip.c +8 -2coreutils/link.c +2 -3include/bb_archive.h +1 -3libbb/copy_file.c +4 -1testsuite/tar.tests +5 -5
archival/libarchive/Kbuild.src+2 -0
@@ -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 \
archival/libarchive/data_extract_all.c+15 -22
@@ -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:
archival/libarchive/unsafe_symlink_target.c+48 -0
@@ -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;
+ }
+}
archival/tar.c+0 -19
@@ -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)
archival/unzip.c+8 -2
@@ -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
coreutils/link.c+2 -3
@@ -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;
include/bb_archive.h+1 -3
@@ -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;
libbb/copy_file.c+4 -1
@@ -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)
testsuite/tar.tests+5 -5
@@ -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