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busybox
libarchive-do-not-extract-unsafe-symlinks-unles...
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File libarchive-do-not-extract-unsafe-symlinks-unless-EXTRACT_UNSAFE_SYMLINKS-1.patch of Package busybox
From: Denys Vlasenko <vda.linux@googlemail.com> Date: Thu Aug 10 11:52:42 2017 +0200 Subject: libarchive: do not extract unsafe symlinks unless $EXTRACT_UNSAFE_SYMLINKS=1 Patch-mainline: bc9bbeb2b81001e8731cd2ae501c8fccc8d87cc7 Git-repo: https://git.busybox.net/busybox Git-commit: 1c7f0c2bf03ff0f95bdfdbec70a6fbd92f08e8e5 References: 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> Signed-off-by: Egbert Eich <eich@suse.de> --- archival/libarchive/Kbuild.src | 2 ++ archival/libarchive/data_extract_all.c | 37 +++++++++------------- archival/libarchive/unsafe_symlink_target.c | 48 +++++++++++++++++++++++++++++ archival/tar.c | 19 ------------ archival/unzip.c | 10 ++++-- include/bb_archive.h | 4 +-- libbb/copy_file.c | 5 ++- testsuite/tar.tests | 10 +++--- 8 files changed, 83 insertions(+), 52 deletions(-) diff --git a/archival/libarchive/Kbuild.src b/archival/libarchive/Kbuild.src index 84117fa85..6310d540e 100644 --- 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 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; + } +} diff --git a/archival/tar.c b/archival/tar.c index fe193ba7e..8e3002ab4 100644 --- a/archival/tar.c +++ b/archival/tar.c @@ -289,23 +289,6 @@ 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) { @@ -1257,8 +1240,6 @@ 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 105d725f0..97a1a031d 100644 --- a/archival/unzip.c +++ b/archival/unzip.c @@ -355,9 +355,15 @@ 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); } diff --git a/include/bb_archive.h b/include/bb_archive.h index d3762415f..d3a02cf18 100644 --- 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 23c0f8320..be9006631 100644 --- 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 1675b07b1..b7cd74ca5 100755 --- 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
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