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b920a38dc

Denys Vlasenko
Denys Vlasenko
2017-07-24
SUCCESS Duration: 143s

Subject

tar: postpone creation of symlinks with "suspicious" targets. Closes 8411

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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/data_extract_all.c +36 -6archival/tar.c +19 -18archival/tar_symlink_attack +16 -0coreutils/link.c +1 -1include/bb_archive.h +4 -0testsuite/tar.tests +54 -11
archival/libarchive/data_extract_all.c+36 -6
@@ -128,10 +128,11 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
res = link(hard_link, dst_name);
if (res != 0 && !(archive_handle->ah_flags & ARCHIVE_EXTRACT_QUIET)) {
/* shared message */
- bb_perror_msg("can't create %slink "
- "%s to %s", "hard",
+ bb_perror_msg("can't create %slink '%s' to '%s'",
+ "hard",
dst_name,
- hard_link);
+ hard_link
+ );
}
/* Hardlinks have no separate mode/ownership, skip chown/chmod */
goto ret;
@@ -178,15 +179,44 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle)
case S_IFLNK:
/* Symlink */
//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.
+ *
+ * For example, consider a .tar created via:
+ * $ tar cvf bug.tar anything.txt
+ * $ ln -s /tmp symlink
+ * $ tar --append -f bug.tar symlink
+ * $ rm symlink
+ * $ mkdir symlink
+ * $ tar --append -f bug.tar symlink/evil.py
+ *
+ * This will result in an archive that contains:
+ * $ tar --list -f bug.tar
+ * anything.txt
+ * symlink [-> /tmp]
+ * symlink/evil.py
+ *
+ * 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",
+ bb_perror_msg("can't create %slink '%s' to '%s'",
+ "sym",
dst_name,
- file_header->link_target);
+ file_header->link_target
+ );
}
break;
case S_IFSOCK:
archival/tar.c+19 -18
@@ -22,24 +22,6 @@
*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
-/* TODO: security with -C DESTDIR option can be enhanced.
- * Consider tar file created via:
- * $ tar cvf bug.tar anything.txt
- * $ ln -s /tmp symlink
- * $ tar --append -f bug.tar symlink
- * $ rm symlink
- * $ mkdir symlink
- * $ tar --append -f bug.tar symlink/evil.py
- *
- * This will result in an archive which contains:
- * $ tar --list -f bug.tar
- * anything.txt
- * symlink
- * symlink/evil.py
- *
- * Untarring it puts evil.py in '/tmp' even if the -C DESTDIR is given.
- * This doesn't feel right, and IIRC GNU tar doesn't do that.
- */
//config:config TAR
//config: bool "tar (40 kb)"
@@ -296,6 +278,23 @@ 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)
{
@@ -1252,6 +1251,8 @@ 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/tar_symlink_attack+16 -0
@@ -0,0 +1,16 @@
+#!/bin/sh
+# Makes "symlink attack" tarball (needs GNU tar for --append)
+
+true >anything.txt
+tar cvf tar_symlink_attack.tar anything.txt
+rm anything.txt
+
+ln -s /tmp symlink
+tar --append -f tar_symlink_attack.tar symlink
+rm symlink
+
+mkdir symlink
+echo BUG >symlink/bb_test_evilfile
+tar --append -f tar_symlink_attack.tar symlink/bb_test_evilfile
+rm symlink/bb_test_evilfile
+rmdir symlink
coreutils/link.c+1 -1
@@ -33,7 +33,7 @@ int link_main(int argc UNUSED_PARAM, char **argv)
if (link(argv[0], argv[1]) != 0) {
/* shared message */
bb_perror_msg_and_die("can't create %slink "
- "%s to %s", "hard",
+ "'%s' to '%s'", "hard",
argv[1], argv[0]
);
}
include/bb_archive.h+4 -0
@@ -64,6 +64,9 @@ 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 *);
@@ -188,6 +191,7 @@ char get_header_ar(archive_handle_t *archive_handle) FAST_FUNC;
char get_header_cpio(archive_handle_t *archive_handle) FAST_FUNC;
char get_header_tar(archive_handle_t *archive_handle) FAST_FUNC;
char get_header_tar_gz(archive_handle_t *archive_handle) FAST_FUNC;
+char get_header_tar_xz(archive_handle_t *archive_handle) FAST_FUNC;
char get_header_tar_bz2(archive_handle_t *archive_handle) FAST_FUNC;
char get_header_tar_lzma(archive_handle_t *archive_handle) FAST_FUNC;
char get_header_tar_xz(archive_handle_t *archive_handle) FAST_FUNC;
testsuite/tar.tests+54 -11
@@ -10,9 +10,6 @@ unset LC_COLLATE
unset LC_ALL
umask 022
-rm -rf tar.tempdir 2>/dev/null
-mkdir tar.tempdir && cd tar.tempdir || exit 1
-
# testing "test name" "script" "expected result" "file input" "stdin"
testing "Empty file is not a tarball" '\
@@ -53,6 +50,7 @@ dd if=/dev/zero bs=512 count=20 2>/dev/null | tar xvf - 2>&1; echo $?
"" ""
SKIP=
+mkdir tar.tempdir && cd tar.tempdir || exit 1
# "tar cf test.tar input input_dir/ input_hard1 input_hard2 input_hard1 input_dir/ input":
# GNU tar 1.26 records as hardlinks:
# input_hard2 -> input_hard1
@@ -64,7 +62,6 @@ SKIP=
# We also don't use "hrw-r--r--" notation for hardlinks in "tar tv" listing.
optional FEATURE_TAR_CREATE FEATURE_LS_SORTFILES
testing "tar hardlinks and repeated files" '\
-rm -rf input_* test.tar 2>/dev/null
>input_hard1
ln input_hard1 input_hard2
mkdir input_dir
@@ -95,10 +92,11 @@ drwxr-xr-x input_dir
" \
"" ""
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+mkdir tar.tempdir && cd tar.tempdir || exit 1
optional FEATURE_TAR_CREATE FEATURE_LS_SORTFILES
testing "tar hardlinks mode" '\
-rm -rf input_* test.tar 2>/dev/null
>input_hard1
chmod 741 input_hard1
ln input_hard1 input_hard2
@@ -128,10 +126,11 @@ Ok: 0
" \
"" ""
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+mkdir tar.tempdir && cd tar.tempdir || exit 1
optional FEATURE_TAR_CREATE FEATURE_LS_SORTFILES
testing "tar symlinks mode" '\
-rm -rf input_* test.tar 2>/dev/null
>input_file
chmod 741 input_file
ln -s input_file input_soft
@@ -159,10 +158,11 @@ lrwxrwxrwx input_file
" \
"" ""
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+mkdir tar.tempdir && cd tar.tempdir || exit 1
optional FEATURE_TAR_CREATE FEATURE_TAR_LONG_OPTIONS
testing "tar --overwrite" "\
-rm -rf input_* test.tar 2>/dev/null
ln input input_hard
tar cf test.tar input_hard
echo WRONG >input
@@ -174,12 +174,13 @@ Ok
" \
"Ok\n" ""
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+mkdir tar.tempdir && cd tar.tempdir || exit 1
test x"$SKIP_KNOWN_BUGS" = x"" && {
# Needs to be run under non-root for meaningful test
optional FEATURE_TAR_CREATE
testing "tar writing into read-only dir" '\
-rm -rf input_* test.tar 2>/dev/null
mkdir input_dir
>input_dir/input_file
chmod 550 input_dir
@@ -201,7 +202,9 @@ dr-xr-x--- input_dir
"" ""
SKIP=
}
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+mkdir tar.tempdir && cd tar.tempdir || exit 1
# Had a bug where on extract autodetect first "switched off" -z
# and then failed to recognize .tgz extension
optional FEATURE_TAR_CREATE FEATURE_SEAMLESS_GZ GUNZIP
@@ -217,7 +220,9 @@ Ok
" \
"" ""
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+mkdir tar.tempdir && cd tar.tempdir || exit 1
# Do we detect XZ-compressed data (even w/o .tar.xz or txz extension)?
# (the uuencoded hello_world.txz contains one empty file named "hello_world")
optional UUDECODE FEATURE_TAR_AUTODETECT FEATURE_SEAMLESS_XZ
@@ -236,7 +241,9 @@ AAAEWVo=
====
"
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+mkdir tar.tempdir && cd tar.tempdir || exit 1
# On extract, everything up to and including last ".." component is stripped
optional FEATURE_TAR_CREATE
testing "tar strips /../ on extract" "\
@@ -255,7 +262,9 @@ Ok
" \
"" ""
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+mkdir tar.tempdir && cd tar.tempdir || exit 1
# attack.tar.bz2 has symlink pointing to a system file
# followed by a regular file with the same name
# containing "root::0:0::/root:/bin/sh":
@@ -270,6 +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'
0
" \
"" "\
@@ -281,12 +291,15 @@ l4/V8LDoe90yiWJhOJvIypgEfxdyRThQkBVn/bI=
====
"
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+
+mkdir tar.tempdir && cd tar.tempdir || exit 1
# And same with -k
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 open 'passwd': File exists
+tar: can't create symlink 'passwd' to '/tmp/passwd'
0
" \
"" "\
@@ -298,7 +311,9 @@ l4/V8LDoe90yiWJhOJvIypgEfxdyRThQkBVn/bI=
====
"
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
+mkdir tar.tempdir && cd tar.tempdir || exit 1
optional UNICODE_SUPPORT FEATURE_TAR_GNU_EXTENSIONS FEATURE_SEAMLESS_BZ2 FEATURE_TAR_AUTODETECT
testing "Pax-encoded UTF8 names and symlinks" '\
tar xvf ../tar.utf8.tar.bz2 2>&1; echo $?
@@ -318,8 +333,36 @@ etc/ssl/certs/f80cc7f6.0 -> EBG_Elektronik_Sertifika_Hizmet_Sağlayıcısı.pem
" \
"" ""
SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
-
-cd .. && rm -rf tar.tempdir || exit 1
+mkdir tar.tempdir && cd tar.tempdir || exit 1
+optional FEATURE_SEAMLESS_BZ2 FEATURE_TAR_AUTODETECT
+testing "Symlink attack: create symlink and then write through it" '\
+exec 2>&1
+uudecode -o input && tar xvf input; echo $?
+ls /tmp/bb_test_evilfile
+ls bb_test_evilfile
+ls symlink/bb_test_evilfile
+' "\
+anything.txt
+symlink
+symlink/bb_test_evilfile
+tar: can't create symlink 'symlink' to '/tmp'
+1
+ls: /tmp/bb_test_evilfile: No such file or directory
+ls: bb_test_evilfile: No such file or directory
+symlink/bb_test_evilfile
+" \
+"" "\
+begin-base64 644 tar_symlink_attack.tar.bz2
+QlpoOTFBWSZTWZgs7bQAALT/hMmQAFBAAf+AEMAGJPPv32AAAIAIMAC5thlR
+omAjAmCMADQT1BqNE0AEwAAjAEwElTKeo9NTR6h6gaeoA0DQNLVdwZZ5iNTk
+AQwCAV6S00QFJYhrlfFkVCEDEGtgNVqYrI0uK3ggnt30gqk4e1TTQm5QIAKa
+SJqzRGSFLMmOloHSAcvLiFxxRiQtQZF+qPxbo173ZDISOAoNoPN4PQPhBhKS
+n8fYaKlioCTzL2oXYczyUUIP4u5IpwoSEwWdtoA=
+====
+"
+SKIP=
+cd .. || exit 1; rm -rf tar.tempdir 2>/dev/null
exit $FAILCOUNT