From bc9bbeb2b81001e8731cd2ae501c8fccc8d87cc7 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Thu, 10 Aug 2017 11:52:42 +0200 Subject: 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 --- archival/libarchive/Kbuild.src | 2 ++ archival/libarchive/data_extract_all.c | 37 +++++++++------------- archival/libarchive/unsafe_symlink_target.c | 48 +++++++++++++++++++++++++++++ 3 files changed, 65 insertions(+), 22 deletions(-) create mode 100644 archival/libarchive/unsafe_symlink_target.c (limited to 'archival/libarchive') diff --git a/archival/libarchive/Kbuild.src b/archival/libarchive/Kbuild.src index 942e755b9..e1a8a7529 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; + } +} -- cgit v1.2.3