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busybox.20467
tar-postpone-creation-of-symlinks-with-suspicio...
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File tar-postpone-creation-of-symlinks-with-suspicious-targets.-Closes-8411.patch of Package busybox.20467
From: Denys Vlasenko <vda.linux@googlemail.com> Date: Mon Jul 24 17:20:13 2017 +0200 Subject: tar: postpone creation of symlinks with "suspicious" targets. Closes 8411 Patch-mainline: 052a622a23260c2f9948fa4b2c460bcc542a0cd0 Git-repo: https://git.busybox.net/busybox Git-commit: 4b0cff49de958f6c03a99c0799c3e408ae29f306 References: function old new delta data_extract_all 968 1038 +70 tar_main 952 986 +34 scan_tree 258 262 +4 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 3/0 up/down: 108/0) Total: 108 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com> Signed-off-by: Egbert Eich <eich@suse.de> --- archival/libarchive/data_extract_all.c | 44 +++++++++++++++++++---- archival/tar.c | 37 +++++++++---------- archival/tar_symlink_attack | 16 +++++++++ include/bb_archive.h | 4 +++ testsuite/tar.tests | 65 ++++++++++++++++++++++++++++------ 5 files changed, 131 insertions(+), 35 deletions(-) diff --git a/archival/libarchive/data_extract_all.c b/archival/libarchive/data_extract_all.c index bd034afdc..1ce927c2f 100644 --- a/archival/libarchive/data_extract_all.c +++ b/archival/libarchive/data_extract_all.c @@ -127,10 +127,12 @@ void FAST_FUNC data_extract_all(archive_handle_t *archive_handle) if (hard_link) { res = link(hard_link, dst_name); if (res != 0 && !(archive_handle->ah_flags & ARCHIVE_EXTRACT_QUIET)) { - bb_perror_msg("can't create %slink " - "from %s to %s", "hard", + /* shared message */ + 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; @@ -177,14 +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) ) { - bb_perror_msg("can't create %slink " - "from %s to %s", "sym", + /* shared message */ + 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: diff --git a/archival/tar.c b/archival/tar.c index 8e315c610..fe193ba7e 100644 --- a/archival/tar.c +++ b/archival/tar.c @@ -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" @@ -307,6 +289,23 @@ 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) { @@ -1258,6 +1257,8 @@ 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) diff --git a/archival/tar_symlink_attack b/archival/tar_symlink_attack new file mode 100755 index 000000000..35455f200 --- /dev/null +++ b/archival/tar_symlink_attack @@ -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 diff --git a/include/bb_archive.h b/include/bb_archive.h index 2b9c5f04c..d3762415f 100644 --- a/include/bb_archive.h +++ b/include/bb_archive.h @@ -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; diff --git a/testsuite/tar.tests b/testsuite/tar.tests index 9f7ce1587..1675b07b1 100755 --- a/testsuite/tar.tests +++ b/testsuite/tar.tests @@ -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
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