This second version contains only the portable part of the sandboxing,
switching to a different user when a new option, 'SandboxUser', is set.
To sum up the changes from the last version:
- The non-portable parts (preventing new privileges from being gained, dropping
capabilities, syscalls filtering and filesystem protection) are gone for now,
I'll propose them via smaller patches if this change is accepted.
- The value returned by the sub-process is now passed by the exit status only,
instead of using a pipe.
- The 'UseSandbox' option has been removed.
- The alpm_sandbox.{c,h} files have been renamed to sandbox.{c,h}.
- A short description of the 'SandboxUser' option has been added to
pacman.conf.5.
Cheers,
Remi
Signed-off-by: Remi Gacogne <[email protected]>
---
doc/pacman.conf.5.asciidoc | 5 ++
lib/libalpm/alpm.h | 5 ++
lib/libalpm/dload.c | 102 ++++++++++++++++++++++++++++++++++++-
lib/libalpm/handle.c | 13 +++++
lib/libalpm/handle.h | 1 +
lib/libalpm/meson.build | 1 +
lib/libalpm/sandbox.c | 63 +++++++++++++++++++++++
lib/libalpm/sandbox.h | 31 +++++++++++
src/pacman/conf.c | 19 ++++++-
src/pacman/conf.h | 1 +
src/pacman/pacman-conf.c | 3 ++
11 files changed, 241 insertions(+), 3 deletions(-)
create mode 100644 lib/libalpm/sandbox.c
create mode 100644 lib/libalpm/sandbox.h
diff --git doc/pacman.conf.5.asciidoc doc/pacman.conf.5.asciidoc
index 77a3907f..5b20b177 100644
--- doc/pacman.conf.5.asciidoc
+++ doc/pacman.conf.5.asciidoc
@@ -207,6 +207,11 @@ Options
positive integer. If this config option is not set then only one
download
stream is used (i.e. downloads happen sequentially).
+*SandboxUser =* username::
+ Specifies the user to switch to for sensitive operations, like
downloading
+ files. That user should exist on the system and have the permissions to
+ write to the files located in `DBPath`. If this config option is not set
+ then these operations are done as the user running pacman.
Repository Sections
-------------------
diff --git lib/libalpm/alpm.h lib/libalpm/alpm.h
index a5f4a6ae..5473558a 100644
--- lib/libalpm/alpm.h
+++ lib/libalpm/alpm.h
@@ -1837,6 +1837,11 @@ int alpm_option_set_gpgdir(alpm_handle_t *handle, const
char *gpgdir);
/* End of gpdir accessors */
/** @} */
+/** Sets the user to switch to for sensitive operations like downloading a
file.
+ * @param handle the context handle
+ * @param sandboxuser the user to set
+ */
+int alpm_option_set_sandboxuser(alpm_handle_t *handle, const char
*sandboxuser);
/** @name Accessors for use syslog
*
diff --git lib/libalpm/dload.c lib/libalpm/dload.c
index 4322318b..03e74ae2 100644
--- lib/libalpm/dload.c
+++ lib/libalpm/dload.c
@@ -28,6 +28,7 @@
#include <sys/time.h>
#include <sys/types.h>
#include <sys/stat.h>
+#include <sys/wait.h>
#include <signal.h>
#ifdef HAVE_NETINET_IN_H
@@ -46,6 +47,7 @@
#include "alpm_list.h"
#include "alpm.h"
#include "log.h"
+#include "sandbox.h"
#include "util.h"
#include "handle.h"
@@ -937,6 +939,100 @@ static int curl_download_internal(alpm_handle_t *handle,
#endif
+/* Download the requested files by launching a process inside a sandbox.
+ * Returns -1 if an error happened for a required file
+ * Returns 0 if a payload was actually downloaded
+ * Returns 1 if no files were downloaded and all errors were non-fatal
+ */
+static int curl_download_internal_sandboxed(alpm_handle_t *handle,
+ alpm_list_t *payloads /* struct dload_payload */,
+ const char *localpath)
+{
+ int pid, err = 0, ret = -1;
+ sigset_t oldblock;
+ struct sigaction sa_ign = { .sa_handler = SIG_IGN }, oldint, oldquit;
+
+ sigaction(SIGINT, &sa_ign, &oldint);
+ sigaction(SIGQUIT, &sa_ign, &oldquit);
+ sigaddset(&sa_ign.sa_mask, SIGCHLD);
+ sigprocmask(SIG_BLOCK, &sa_ign.sa_mask, &oldblock);
+
+ pid = fork();
+
+ /* child */
+ if(pid == 0) {
+ /* restore signal handling for the child to inherit */
+ sigaction(SIGINT, &oldint, NULL);
+ sigaction(SIGQUIT, &oldquit, NULL);
+ sigprocmask(SIG_SETMASK, &oldblock, NULL);
+
+ /* cwd to the download directory */
+ ret = chdir(localpath);
+ if(ret != 0) {
+ _alpm_log(handle, ALPM_LOG_WARNING, _("could not chdir
to download directory %s\n"), localpath);
+ ret = -1;
+ } else {
+ ret = alpm_sandbox_child(handle->sandboxuser);
+ if (ret != 0) {
+ _alpm_log(handle, ALPM_LOG_WARNING,
_("sandboxing failed!\n"));
+ }
+
+ ret = curl_download_internal(handle, payloads,
localpath);
+ }
+
+ /* pass the result back to the parent */
+ if(ret == 0) {
+ /* a payload was actually downloaded */
+ _Exit(0);
+ }
+ else if(ret == 1) {
+ /* no files were downloaded and all errors were
non-fatal */
+ _Exit(1);
+ }
+ else {
+ /* an error happened for a required file */
+ _Exit(2);
+ }
+ }
+
+ /* parent */
+
+ if(pid != -1) {
+ int wret;
+ while((wret = waitpid(pid, &ret, 0)) == -1 && errno == EINTR);
+ if(wret > 0) {
+ if(!WIFEXITED(ret)) {
+ /* the child did not terminate normally */
+ ret = -1;
+ }
+ else {
+ ret = WIFEXITED(ret);
+ if(ret != 0 && ret != 1) {
+ /* an error happened for a required
file, or unexpected exit status */
+ ret = -1;
+ }
+ }
+ }
+ else {
+ /* waitpid failed */
+ err = errno;
+ }
+ } else {
+ /* fork failed, make sure errno is preserved after cleanup */
+ err = errno;
+ }
+
+ sigaction(SIGINT, &oldint, NULL);
+ sigaction(SIGQUIT, &oldquit, NULL);
+ sigprocmask(SIG_SETMASK, &oldblock, NULL);
+
+ if(err) {
+ errno = err;
+ ret = -1;
+ }
+ return ret;
+}
+
/* Returns -1 if an error happened for a required file
* Returns 0 if a payload was actually downloaded
* Returns 1 if no files were downloaded and all errors were non-fatal
@@ -947,7 +1043,11 @@ int _alpm_download(alpm_handle_t *handle,
{
if(handle->fetchcb == NULL) {
#ifdef HAVE_LIBCURL
- return curl_download_internal(handle, payloads, localpath);
+ if(handle->sandboxuser) {
+ return curl_download_internal_sandboxed(handle,
payloads, localpath);
+ } else {
+ return curl_download_internal(handle, payloads,
localpath);
+ }
#else
RET_ERR(handle, ALPM_ERR_EXTERNAL_DOWNLOAD, -1);
#endif
diff --git lib/libalpm/handle.c lib/libalpm/handle.c
index e6b683cb..5c914faa 100644
--- lib/libalpm/handle.c
+++ lib/libalpm/handle.c
@@ -573,6 +573,19 @@ int SYMEXPORT alpm_option_set_gpgdir(alpm_handle_t
*handle, const char *gpgdir)
return 0;
}
+int SYMEXPORT alpm_option_set_sandboxuser(alpm_handle_t *handle, const char
*sandboxuser)
+{
+ CHECK_HANDLE(handle, return -1);
+ if(handle->sandboxuser) {
+ FREE(handle->sandboxuser);
+ }
+
+ STRDUP(handle->sandboxuser, sandboxuser, RET_ERR(handle,
ALPM_ERR_MEMORY, -1));
+
+ _alpm_log(handle, ALPM_LOG_DEBUG, "option 'sandboxuser' = %s\n",
handle->sandboxuser);
+ return 0;
+}
+
int SYMEXPORT alpm_option_set_usesyslog(alpm_handle_t *handle, int usesyslog)
{
CHECK_HANDLE(handle, return -1);
diff --git lib/libalpm/handle.h lib/libalpm/handle.h
index b1526c67..e0587fc7 100644
--- lib/libalpm/handle.h
+++ lib/libalpm/handle.h
@@ -90,6 +90,7 @@ struct __alpm_handle_t {
char *logfile; /* Name of the log file */
char *lockfile; /* Name of the lock file */
char *gpgdir; /* Directory where GnuPG files are stored */
+ char *sandboxuser; /* User to switch to for sensitive operations
like downloading files */
alpm_list_t *cachedirs; /* Paths to pacman cache directories */
alpm_list_t *hookdirs; /* Paths to hook directories */
alpm_list_t *overwrite_files; /* Paths that may be overwritten */
diff --git lib/libalpm/meson.build lib/libalpm/meson.build
index 607e91a3..224fbf5f 100644
--- lib/libalpm/meson.build
+++ lib/libalpm/meson.build
@@ -24,6 +24,7 @@ libalpm_sources = files('''
pkghash.h pkghash.c
rawstr.c
remove.h remove.c
+ sandbox.h sandbox.c
signing.c signing.h
sync.h sync.c
trans.h trans.c
diff --git lib/libalpm/sandbox.c lib/libalpm/sandbox.c
new file mode 100644
index 00000000..3c491176
--- /dev/null
+++ lib/libalpm/sandbox.c
@@ -0,0 +1,63 @@
+/*
+ * sandbox.c
+ *
+ * Copyright (c) 2021 Pacman Development Team <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <grp.h>
+#include <pwd.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "sandbox.h"
+
+static int switch_to_user(const char *user)
+{
+ struct passwd const *pw = NULL;
+ if(getuid() != 0) {
+ return 1;
+ }
+ pw = getpwnam(user);
+ if(pw == NULL) {
+ return errno;
+ }
+ if(setgid(pw->pw_gid) != 0) {
+ return errno;
+ }
+ if(setgroups(0, NULL)) {
+ return errno;
+ }
+ if(setuid(pw->pw_uid) != 0) {
+ return errno;
+ }
+ return 0;
+}
+
+/* check exported library symbols with: nm -C -D <lib> */
+#define SYMEXPORT __attribute__((visibility("default")))
+
+int SYMEXPORT alpm_sandbox_child(const char* sandboxuser)
+{
+ int result = 0;
+
+ if(sandboxuser != NULL) {
+ result = switch_to_user(sandboxuser);
+ }
+
+ return result;
+}
diff --git lib/libalpm/sandbox.h lib/libalpm/sandbox.h
new file mode 100644
index 00000000..47611575
--- /dev/null
+++ lib/libalpm/sandbox.h
@@ -0,0 +1,31 @@
+/*
+ * sandbox.h
+ *
+ * Copyright (c) 2021 Pacman Development Team <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef ALPM_SANDBOX_H
+#define ALPM_SANDBOX_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int alpm_sandbox_child(const char *sandboxuser);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* ALPM_SANDBOX_H */
diff --git src/pacman/conf.c src/pacman/conf.c
index 12fee64c..15d05e8c 100644
--- src/pacman/conf.c
+++ src/pacman/conf.c
@@ -33,6 +33,8 @@
#include <unistd.h>
#include <signal.h>
+#include <sandbox.h>
+
/* pacman */
#include "conf.h"
#include "ini.h"
@@ -215,7 +217,7 @@ static char *get_tempfile(const char *path, const char
*filename)
* - not thread-safe
* - errno may be set by fork(), pipe(), or execvp()
*/
-static int systemvp(const char *file, char *const argv[])
+static int systemvp(const char *file, char *const argv[], const char
*sandboxuser)
{
int pid, err = 0, ret = -1, err_fd[2];
sigset_t oldblock;
@@ -242,6 +244,13 @@ static int systemvp(const char *file, char *const argv[])
sigaction(SIGQUIT, &oldquit, NULL);
sigprocmask(SIG_SETMASK, &oldblock, NULL);
+ if (sandboxuser) {
+ ret = alpm_sandbox_child(sandboxuser);
+ if (ret != 0) {
+ pm_printf(ALPM_LOG_WARNING, _("Switching to
sandbox user %s failed!\n"), sandboxuser);
+ }
+ }
+
execvp(file, argv);
/* execvp failed, pass the error back to the parent */
@@ -352,7 +361,7 @@ static int download_with_xfercommand(void *ctx, const char
*url,
free(cmd);
}
}
- retval = systemvp(argv[0], (char**)argv);
+ retval = systemvp(argv[0], (char**)argv, config->sandboxuser);
if(retval == -1) {
pm_printf(ALPM_LOG_WARNING, _("running XferCommand: fork
failed!\n"));
@@ -668,6 +677,11 @@ static int _parse_options(const char *key, char *value,
config->logfile = strdup(value);
pm_printf(ALPM_LOG_DEBUG, "config: logfile:
%s\n", value);
}
+ } else if(strcmp(key, "SandboxUser") == 0) {
+ if(!config->sandboxuser) {
+ config->sandboxuser = strdup(value);
+ pm_printf(ALPM_LOG_DEBUG, "config: sandboxuser:
%s\n", value);
+ }
} else if(strcmp(key, "XferCommand") == 0) {
char **c;
if((config->xfercommand_argv = wordsplit(value)) ==
NULL) {
@@ -904,6 +918,7 @@ static int setup_libalpm(void)
alpm_option_set_architectures(handle, config->architectures);
alpm_option_set_checkspace(handle, config->checkspace);
alpm_option_set_usesyslog(handle, config->usesyslog);
+ alpm_option_set_sandboxuser(handle, config->sandboxuser);
alpm_option_set_ignorepkgs(handle, config->ignorepkg);
alpm_option_set_ignoregroups(handle, config->ignoregrp);
diff --git src/pacman/conf.h src/pacman/conf.h
index 04350d39..675e06fb 100644
--- src/pacman/conf.h
+++ src/pacman/conf.h
@@ -67,6 +67,7 @@ typedef struct __config_t {
char *logfile;
char *gpgdir;
char *sysroot;
+ char *sandboxuser;
alpm_list_t *hookdirs;
alpm_list_t *cachedirs;
alpm_list_t *architectures;
diff --git src/pacman/pacman-conf.c src/pacman/pacman-conf.c
index 600f1622..05a6bcd8 100644
--- src/pacman/pacman-conf.c
+++ src/pacman/pacman-conf.c
@@ -251,6 +251,7 @@ static void dump_config(void)
show_list_str("HookDir", config->hookdirs);
show_str("GPGDir", config->gpgdir);
show_str("LogFile", config->logfile);
+ show_str("SandboxUser", config->sandboxuser);
show_list_str("HoldPkg", config->holdpkg);
show_list_str("IgnorePkg", config->ignorepkg);
@@ -349,6 +350,8 @@ static int list_directives(void)
show_str("GPGDir", config->gpgdir);
} else if(strcasecmp(i->data, "LogFile") == 0) {
show_str("LogFile", config->logfile);
+ } else if(strcasecmp(i->data, "SandboxUser") == 0) {
+ show_str("SandboxUser", config->sandboxuser);
} else if(strcasecmp(i->data, "HoldPkg") == 0) {
show_list_str("HoldPkg", config->holdpkg);
--
2.33.0
