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

Browse Source 
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>
This commit is contained in:
Denys Vlasenko 2017-08-10 11:52:42 +02:00
parent 0cf64c8b5d
commit bc9bbeb2b8
9 changed files with 85 additions and 55 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
archival/libarchive/Kbuild.src
View File

@ -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 \

37
archival/libarchive/data_extract_all.c
View File

@ -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:

48
archival/libarchive/unsafe_symlink_target.c Normal file
View File

@ -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;
}
}

19
archival/tar.c
View File

@ -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)

10
archival/unzip.c
View File

@ -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

5
coreutils/link.c
View File

@ -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;

4
include/bb_archive.h
View File

@ -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;

5
libbb/copy_file.c
View File

@ -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)

10
testsuite/tar.tests
View File

@ -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