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rework unpacking of packages and harden package file format requirements
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A crafted .apk file could to trick apk writing unverified data to
an unexpected file during temporary file creation due to bugs in handling
long link target name and the way a regular file is extracted.

Several hardening steps are implemented to avoid this:
 - the temporary file is now always first unlinked (apk thus reserved
   all filenames .apk.* to be it's working files)
 - the temporary file is after that created with O_EXCL to avoid races
 - the temporary file is no longer directly the archive entry name
   and thus directly controlled by potentially untrusted data
 - long file names and link target names are now rejected
 - hard link targets are now more rigorously checked
 - various additional checks added for the extraction process to
   error out early in case of malformed (or old legacy) file

Reported-by: Max Justicz <max@justi.cz>
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@fabled
fabled committed Sep 10, 2018
1 parent b11f9aa commit 6484ed9
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Showing 6 changed files with 142 additions and 105 deletions.
3 changes: 2 additions & 1 deletion src/apk_archive.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,8 @@ int apk_tar_write_entry(struct apk_ostream *, const struct apk_file_info *ae,
int apk_tar_write_padding(struct apk_ostream *, const struct apk_file_info *ae);

int apk_archive_entry_extract(int atfd, const struct apk_file_info *ae,
const char *suffix, struct apk_istream *is,
const char *extract_name, const char *hardlink_name,
struct apk_istream *is,
apk_progress_cb cb, void *cb_ctx);

#endif
34 changes: 13 additions & 21 deletions src/archive.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -317,6 +317,12 @@ int apk_tar_parse(struct apk_istream *is, apk_archive_entry_parser parser,
break;
}

if (strnlen(entry.name, PATH_MAX) >= PATH_MAX-10 ||
(entry.link_target && strnlen(entry.link_target, PATH_MAX) >= PATH_MAX-10)) {
r = -ENAMETOOLONG;
goto err;
}

teis.bytes_left = entry.size;
if (entry.mode & S_IFMT) {
/* callback parser function */
Expand Down Expand Up @@ -428,23 +434,15 @@ int apk_tar_write_padding(struct apk_ostream *os, const struct apk_file_info *ae
}

int apk_archive_entry_extract(int atfd, const struct apk_file_info *ae,
const char *suffix, struct apk_istream *is,
const char *extract_name, const char *link_target,
struct apk_istream *is,
apk_progress_cb cb, void *cb_ctx)
{
struct apk_xattr *xattr;
char *fn = ae->name;
const char *fn = extract_name ?: ae->name;
int fd, r = -1, atflags = 0, ret = 0;

if (suffix != NULL) {
fn = alloca(PATH_MAX);
snprintf(fn, PATH_MAX, "%s%s", ae->name, suffix);
}

if ((!S_ISDIR(ae->mode) && !S_ISREG(ae->mode)) ||
(ae->link_target != NULL)) {
/* non-standard entries need to be deleted first */
unlinkat(atfd, fn, 0);
}
if (unlinkat(atfd, fn, 0) != 0 && errno != ENOENT) return -errno;

switch (ae->mode & S_IFMT) {
case S_IFDIR:
Expand All @@ -454,7 +452,7 @@ int apk_archive_entry_extract(int atfd, const struct apk_file_info *ae,
break;
case S_IFREG:
if (ae->link_target == NULL) {
int flags = O_RDWR | O_CREAT | O_TRUNC | O_CLOEXEC;
int flags = O_RDWR | O_CREAT | O_TRUNC | O_CLOEXEC | O_EXCL;

fd = openat(atfd, fn, flags, ae->mode & 07777);
if (fd < 0) {
Expand All @@ -465,18 +463,12 @@ int apk_archive_entry_extract(int atfd, const struct apk_file_info *ae,
if (r != ae->size) ret = r < 0 ? r : -ENOSPC;
close(fd);
} else {
char *link_target = ae->link_target;
if (suffix != NULL) {
link_target = alloca(PATH_MAX);
snprintf(link_target, PATH_MAX, "%s%s",
ae->link_target, suffix);
}
r = linkat(atfd, link_target, atfd, fn, 0);
r = linkat(atfd, link_target ?: ae->link_target, atfd, fn, 0);
if (r < 0) ret = -errno;
}
break;
case S_IFLNK:
r = symlinkat(ae->link_target, atfd, fn);
r = symlinkat(link_target ?: ae->link_target, atfd, fn);
if (r < 0) ret = -errno;
atflags |= AT_SYMLINK_NOFOLLOW;
break;
Expand Down
4 changes: 2 additions & 2 deletions src/commit.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -232,8 +232,8 @@ static int run_commit_hook(void *ctx, int dirfd, const char *file)
struct apk_database *db = hook->db;
char fn[PATH_MAX], *argv[] = { fn, (char *) commit_hook_str[hook->type], NULL };

if ((apk_flags & (APK_NO_SCRIPTS | APK_SIMULATE)) != 0)
return 0;
if (file[0] == '.') return 0;
if ((apk_flags & (APK_NO_SCRIPTS | APK_SIMULATE)) != 0) return 0;

snprintf(fn, sizeof(fn), "etc/apk/commit_hooks.d" "/%s", file);
if ((apk_flags & APK_NO_COMMIT_HOOKS) != 0) {
Expand Down
160 changes: 107 additions & 53 deletions src/database.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -828,8 +828,9 @@ int apk_db_index_read(struct apk_database *db, struct apk_bstream *bs, int repo)
case 'F':
if (diri) apk_db_dir_apply_diri_permissions(diri);
if (pkg->name == NULL) goto bad_entry;
diri = apk_db_diri_new(db, pkg, l, &diri_node);
file_diri_node = &diri->owned_files.first;
diri = find_diri(ipkg, l, NULL, &diri_node);
if (!diri) diri = apk_db_diri_new(db, pkg, l, &diri_node);
file_diri_node = hlist_tail_ptr(&diri->owned_files);
break;
case 'a':
if (file == NULL) goto bad_entry;
Expand Down Expand Up @@ -2358,6 +2359,31 @@ static struct apk_db_dir_instance *apk_db_install_directory_entry(struct install
return diri;
}

#define TMPNAME_MAX (PATH_MAX + 64)

static const char *format_tmpname(struct apk_package *pkg, struct apk_db_file *f, char tmpname[static TMPNAME_MAX])
{
EVP_MD_CTX mdctx;
unsigned char md[EVP_MAX_MD_SIZE];
apk_blob_t b = APK_BLOB_PTR_LEN(tmpname, TMPNAME_MAX);

if (!f) return NULL;

EVP_DigestInit(&mdctx, EVP_sha256());
EVP_DigestUpdate(&mdctx, pkg->name->name, strlen(pkg->name->name) + 1);
EVP_DigestUpdate(&mdctx, f->diri->dir->name, f->diri->dir->namelen);
EVP_DigestUpdate(&mdctx, "/", 1);
EVP_DigestUpdate(&mdctx, f->name, f->namelen);
EVP_DigestFinal(&mdctx, md, NULL);

apk_blob_push_blob(&b, APK_BLOB_PTR_LEN(f->diri->dir->name, f->diri->dir->namelen));
apk_blob_push_blob(&b, APK_BLOB_STR("/.apk."));
apk_blob_push_hexdump(&b, APK_BLOB_PTR_LEN((char *)md, 24));
apk_blob_push_blob(&b, APK_BLOB_PTR_LEN("", 1));

return tmpname;
}

static int apk_db_install_archive_entry(void *_ctx,
const struct apk_file_info *ae,
struct apk_istream *is)
Expand All @@ -2369,8 +2395,9 @@ static int apk_db_install_archive_entry(void *_ctx,
struct apk_installed_package *ipkg = pkg->ipkg;
apk_blob_t name = APK_BLOB_STR(ae->name), bdir, bfile;
struct apk_db_dir_instance *diri = ctx->diri;
struct apk_db_file *file;
struct apk_db_file *file, *link_target_file = NULL;
int ret = 0, r, type = APK_SCRIPT_INVALID;
char tmpname_file[TMPNAME_MAX], tmpname_link_target[TMPNAME_MAX];

r = apk_sign_ctx_process_file(&ctx->sctx, ae, is);
if (r <= 0)
Expand Down Expand Up @@ -2437,6 +2464,40 @@ static int apk_db_install_archive_entry(void *_ctx,
diri = apk_db_install_directory_entry(ctx, bdir);
}

/* Check hard link target to exist in this package */
if (S_ISREG(ae->mode) && ae->link_target) {
do {
struct apk_db_file *lfile;
struct apk_db_dir_instance *ldiri;
struct hlist_node *n;
apk_blob_t hldir, hlfile;

if (!apk_blob_rsplit(APK_BLOB_STR(ae->link_target),
'/', &hldir, &hlfile))
break;

ldiri = find_diri(ipkg, hldir, diri, NULL);
if (ldiri == NULL)
break;

hlist_for_each_entry(lfile, n, &ldiri->owned_files,
diri_files_list) {
if (apk_blob_compare(APK_BLOB_PTR_LEN(lfile->name, lfile->namelen),
hlfile) == 0) {
link_target_file = lfile;
break;
}
}
} while (0);

if (!link_target_file) {
apk_error(PKG_VER_FMT": "BLOB_FMT": no hard link target (%s) in archive",
PKG_VER_PRINTF(pkg), BLOB_PRINTF(name), ae->link_target);
ipkg->broken_files = 1;
return 0;
}
}

opkg = NULL;
file = apk_db_file_query(db, bdir, bfile);
if (file != NULL) {
Expand Down Expand Up @@ -2495,41 +2556,21 @@ static int apk_db_install_archive_entry(void *_ctx,
if (apk_verbosity >= 3)
apk_message("%s", ae->name);

/* Extract the file as name.apk-new */
/* Extract the file with temporary name */
file->acl = apk_db_acl_atomize(ae->mode, ae->uid, ae->gid, &ae->xattr_csum);
r = apk_archive_entry_extract(db->root_fd, ae, ".apk-new", is,
extract_cb, ctx);
r = apk_archive_entry_extract(
db->root_fd, ae,
format_tmpname(pkg, file, tmpname_file),
format_tmpname(pkg, link_target_file, tmpname_link_target),
is, extract_cb, ctx);

switch (r) {
case 0:
/* Hardlinks need special care for checksum */
if (ae->csum.type == APK_CHECKSUM_NONE &&
ae->link_target != NULL) {
do {
struct apk_db_file *lfile;
struct apk_db_dir_instance *ldiri;
struct hlist_node *n;

if (!apk_blob_rsplit(APK_BLOB_STR(ae->link_target),
'/', &bdir, &bfile))
break;

ldiri = find_diri(ipkg, bdir, diri, NULL);
if (ldiri == NULL)
break;

hlist_for_each_entry(lfile, n, &ldiri->owned_files,
diri_files_list) {
if (apk_blob_compare(APK_BLOB_PTR_LEN(lfile->name, lfile->namelen),
bfile) == 0) {
memcpy(&file->csum, &lfile->csum,
sizeof(file->csum));
break;
}
}
} while (0);
} else
memcpy(&file->csum, &ae->csum, sizeof(file->csum));
if (link_target_file)
memcpy(&file->csum, &link_target_file->csum, sizeof file->csum);
else
memcpy(&file->csum, &ae->csum, sizeof file->csum);
break;
case -ENOTSUP:
ipkg->broken_xattr = 1;
Expand All @@ -2547,8 +2588,11 @@ static int apk_db_install_archive_entry(void *_ctx,
if (name.ptr[name.len-1] == '/')
name.len--;

diri = apk_db_install_directory_entry(ctx, name);
apk_db_dir_prepare(db, diri->dir, ae->mode);
diri = ctx->diri = find_diri(ipkg, name, NULL, &ctx->file_diri_node);
if (!diri) {
diri = apk_db_install_directory_entry(ctx, name);
apk_db_dir_prepare(db, diri->dir, ae->mode);
}
apk_db_diri_set(diri, apk_db_acl_atomize(ae->mode, ae->uid, ae->gid, &ae->xattr_csum));
}
ctx->installed_size += ctx->current_file_size;
Expand All @@ -2558,25 +2602,24 @@ static int apk_db_install_archive_entry(void *_ctx,

static void apk_db_purge_pkg(struct apk_database *db,
struct apk_installed_package *ipkg,
const char *exten)
int is_installed)
{
struct apk_db_dir_instance *diri;
struct apk_db_file *file;
struct apk_db_file_hash_key key;
struct apk_file_info fi;
struct hlist_node *dc, *dn, *fc, *fn;
unsigned long hash;
char name[PATH_MAX];
char name[TMPNAME_MAX];

hlist_for_each_entry_safe(diri, dc, dn, &ipkg->owned_dirs, pkg_dirs_list) {
if (exten == NULL)
diri->dir->modified = 1;
if (is_installed) diri->dir->modified = 1;

hlist_for_each_entry_safe(file, fc, fn, &diri->owned_files, diri_files_list) {
snprintf(name, sizeof(name),
DIR_FILE_FMT "%s",
DIR_FILE_PRINTF(diri->dir, file),
exten ?: "");
if (is_installed)
snprintf(name, sizeof name, DIR_FILE_FMT, DIR_FILE_PRINTF(diri->dir, file));
else
format_tmpname(ipkg->pkg, file, name);

key = (struct apk_db_file_hash_key) {
.dirname = APK_BLOB_PTR_LEN(diri->dir->name, diri->dir->namelen),
Expand All @@ -2592,7 +2635,7 @@ static void apk_db_purge_pkg(struct apk_database *db,
if (apk_verbosity >= 3)
apk_message("%s", name);
__hlist_del(fc, &diri->owned_files.first);
if (exten == NULL) {
if (is_installed) {
apk_hash_delete_hashed(&db->installed.files, APK_BLOB_BUF(&key), hash);
db->installed.stats.files--;
}
Expand All @@ -2613,18 +2656,16 @@ static void apk_db_migrate_files(struct apk_database *db,
struct apk_file_info fi;
struct hlist_node *dc, *dn, *fc, *fn;
unsigned long hash;
char name[PATH_MAX], tmpname[PATH_MAX];
char name[PATH_MAX], tmpname[TMPNAME_MAX];
int cstype, r;

hlist_for_each_entry_safe(diri, dc, dn, &ipkg->owned_dirs, pkg_dirs_list) {
dir = diri->dir;
dir->modified = 1;

hlist_for_each_entry_safe(file, fc, fn, &diri->owned_files, diri_files_list) {
snprintf(name, sizeof(name), DIR_FILE_FMT,
DIR_FILE_PRINTF(diri->dir, file));
snprintf(tmpname, sizeof(tmpname), DIR_FILE_FMT ".apk-new",
DIR_FILE_PRINTF(diri->dir, file));
snprintf(name, sizeof(name), DIR_FILE_FMT, DIR_FILE_PRINTF(diri->dir, file));
format_tmpname(ipkg->pkg, file, tmpname);

key = (struct apk_db_file_hash_key) {
.dirname = APK_BLOB_PTR_LEN(dir->name, dir->namelen),
Expand Down Expand Up @@ -2665,8 +2706,21 @@ static void apk_db_migrate_files(struct apk_database *db,
APK_FI_NOFOLLOW | file->csum.type, &fi);
if ((apk_flags & APK_CLEAN_PROTECTED) ||
(file->csum.type != APK_CHECKSUM_NONE &&
apk_checksum_compare(&file->csum, &fi.csum) == 0))
apk_checksum_compare(&file->csum, &fi.csum) == 0)) {
unlinkat(db->root_fd, tmpname, 0);
} else {
snprintf(name, sizeof name,
DIR_FILE_FMT ".apk-new",
DIR_FILE_PRINTF(diri->dir, file));
if (renameat(db->root_fd, tmpname,
db->root_fd, name) != 0) {
apk_error(PKG_VER_FMT": failed to rename %s to %s.",
PKG_VER_PRINTF(ipkg->pkg),
tmpname, name);
ipkg->broken_files = 1;
}
}

} else {
/* Overwrite the old file */
if (renameat(db->root_fd, tmpname,
Expand Down Expand Up @@ -2799,7 +2853,7 @@ int apk_db_install_pkg(struct apk_database *db, struct apk_package *oldpkg,
if (ipkg == NULL)
goto ret_r;
apk_ipkg_run_script(ipkg, db, APK_SCRIPT_PRE_DEINSTALL, script_args);
apk_db_purge_pkg(db, ipkg, NULL);
apk_db_purge_pkg(db, ipkg, TRUE);
apk_ipkg_run_script(ipkg, db, APK_SCRIPT_POST_DEINSTALL, script_args);
apk_pkg_uninstall(db, oldpkg);
goto ret_r;
Expand All @@ -2822,15 +2876,15 @@ int apk_db_install_pkg(struct apk_database *db, struct apk_package *oldpkg,
cb, cb_ctx, script_args);
if (r != 0) {
if (oldpkg != newpkg)
apk_db_purge_pkg(db, ipkg, ".apk-new");
apk_db_purge_pkg(db, ipkg, FALSE);
apk_pkg_uninstall(db, newpkg);
goto ret_r;
}
apk_db_migrate_files(db, ipkg);
}

if (oldpkg != NULL && oldpkg != newpkg && oldpkg->ipkg != NULL) {
apk_db_purge_pkg(db, oldpkg->ipkg, NULL);
apk_db_purge_pkg(db, oldpkg->ipkg, TRUE);
apk_pkg_uninstall(db, oldpkg);
}

Expand Down
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