IPA: Move setting the SELinux context to a child process

In order for the sssd_be process to run as unprivileged user, we need to
move the semanage processing to a process that runs as the root user
using setuid privileges.

Reviewed-by: Michal Židek <mzidek@redhat.com>

1 files changed, 272 insertions, 0 deletions

diff --git a/src/providers/ipa/selinux_child.c b/src/providers/ipa/selinux_child.c
new file mode 100644
index 000000000..a624cfd30
--- /dev/null
+++ b/src/providers/ipa/selinux_child.c
@@ -0,0 +1,272 @@
+/*
+    SSSD
+
+    IPA back end -- set SELinux context in a child module
+
+    Authors:
+        Jakub Hrozek <jhrozek@redhat.com>
+
+    Copyright (C) 2014 Red Hat
+
+    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 3 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 <sys/types.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <popt.h>
+
+#include "util/util.h"
+#include "util/child_common.h"
+#include "providers/dp_backend.h"
+
+struct input_buffer {
+    const char *seuser;
+    const char *mls_range;
+    const char *username;
+};
+
+static errno_t unpack_buffer(uint8_t *buf,
+                             size_t size,
+                             struct input_buffer *ibuf)
+{
+    size_t p = 0;
+    uint32_t len;
+
+    /* seuser */
+    SAFEALIGN_COPY_UINT32_CHECK(&len, buf + p, size, &p);
+    DEBUG(SSSDBG_TRACE_INTERNAL, "seuser length: %d\n", len);
+    if (len == 0) {
+        return EINVAL;
+    } else {
+        if ((p + len ) > size) return EINVAL;
+        ibuf->seuser = talloc_strndup(ibuf, (char *)(buf + p), len);
+        if (ibuf->seuser == NULL) return ENOMEM;
+        DEBUG(SSSDBG_TRACE_INTERNAL, "seuser: %s\n", ibuf->seuser);
+        p += len;
+    }
+
+    /* MLS range */
+    SAFEALIGN_COPY_UINT32_CHECK(&len, buf + p, size, &p);
+    DEBUG(SSSDBG_TRACE_INTERNAL, "mls_range length: %d\n", len);
+    if (len == 0) {
+        return EINVAL;
+    } else {
+        if ((p + len ) > size) return EINVAL;
+        ibuf->mls_range = talloc_strndup(ibuf, (char *)(buf + p), len);
+        if (ibuf->mls_range == NULL) return ENOMEM;
+        DEBUG(SSSDBG_TRACE_INTERNAL, "mls_range: %s\n", ibuf->mls_range);
+        p += len;
+    }
+
+    /* username */
+    SAFEALIGN_COPY_UINT32_CHECK(&len, buf + p, size, &p);
+    DEBUG(SSSDBG_TRACE_INTERNAL, "username length: %d\n", len);
+    if (len == 0) {
+        return EINVAL;
+    } else {
+        if ((p + len ) > size) return EINVAL;
+        ibuf->username = talloc_strndup(ibuf, (char *)(buf + p), len);
+        if (ibuf->username == NULL) return ENOMEM;
+        DEBUG(SSSDBG_TRACE_INTERNAL, "username: %s\n", ibuf->username);
+        p += len;
+    }
+
+    return EOK;
+}
+
+static errno_t pack_buffer(struct response *r, int result)
+{
+    size_t p = 0;
+
+    /* A buffer with the following structure must be created:
+     *   uint32_t status of the request (required)
+     */
+    r->size =  sizeof(uint32_t);
+
+    r->buf = talloc_array(r, uint8_t, r->size);
+    if(r->buf == NULL) {
+        return ENOMEM;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, "result [%d]\n", result);
+
+    /* result */
+    SAFEALIGN_SET_UINT32(&r->buf[p], result, &p);
+
+    return EOK;
+}
+
+static errno_t prepare_response(TALLOC_CTX *mem_ctx,
+                                int result,
+                                struct response **rsp)
+{
+    int ret;
+    struct response *r = NULL;
+
+    r = talloc_zero(mem_ctx, struct response);
+    if (r == NULL) {
+        return ENOMEM;
+    }
+
+    r->buf = NULL;
+    r->size = 0;
+
+    ret = pack_buffer(r, result);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "pack_buffer failed\n");
+        return ret;
+    }
+
+    *rsp = r;
+    DEBUG(SSSDBG_TRACE_ALL, "r->size: %zu\n", r->size);
+    return EOK;
+}
+
+int main(int argc, const char *argv[])
+{
+    int opt;
+    poptContext pc;
+    int debug_fd = -1;
+    errno_t ret;
+    TALLOC_CTX *main_ctx = NULL;
+    uint8_t *buf = NULL;
+    ssize_t len = 0;
+    struct input_buffer *ibuf = NULL;
+    struct response *resp = NULL;
+    size_t written;
+
+    struct poptOption long_options[] = {
+        POPT_AUTOHELP
+        {"debug-level", 'd', POPT_ARG_INT, &debug_level, 0,
+         _("Debug level"), NULL},
+        {"debug-timestamps", 0, POPT_ARG_INT, &debug_timestamps, 0,
+         _("Add debug timestamps"), NULL},
+        {"debug-microseconds", 0, POPT_ARG_INT, &debug_microseconds, 0,
+         _("Show timestamps with microseconds"), NULL},
+        {"debug-fd", 0, POPT_ARG_INT, &debug_fd, 0,
+         _("An open file descriptor for the debug logs"), NULL},
+        {"debug-to-stderr", 0, POPT_ARG_NONE | POPT_ARGFLAG_DOC_HIDDEN,
+         &debug_to_stderr, 0,
+         _("Send the debug output to stderr directly."), NULL },
+        POPT_TABLEEND
+    };
+
+    /* Set debug level to invalid value so we can decide if -d 0 was used. */
+    debug_level = SSSDBG_INVALID;
+
+    pc = poptGetContext(argv[0], argc, argv, long_options, 0);
+    while((opt = poptGetNextOpt(pc)) != -1) {
+        switch(opt) {
+        default:
+        fprintf(stderr, "\nInvalid option %s: %s\n\n",
+                  poptBadOption(pc, 0), poptStrerror(opt));
+            poptPrintUsage(pc, stderr, 0);
+            _exit(-1);
+        }
+    }
+
+    poptFreeContext(pc);
+
+    DEBUG_INIT(debug_level);
+
+    debug_prg_name = talloc_asprintf(NULL, "[sssd[selinux_child[%d]]]", getpid());
+    if (debug_prg_name == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "talloc_asprintf failed.\n");
+        goto fail;
+    }
+
+    if (debug_fd != -1) {
+        ret = set_debug_file_from_fd(debug_fd);
+        if (ret != EOK) {
+            DEBUG(SSSDBG_CRIT_FAILURE, "set_debug_file_from_fd failed.\n");
+        }
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, "selinux_child started.\n");
+    DEBUG(SSSDBG_TRACE_INTERNAL,
+          "Running as [%"SPRIuid"][%"SPRIgid"].\n", geteuid(), getegid());
+
+    main_ctx = talloc_new(NULL);
+    if (main_ctx == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "talloc_new failed.\n");
+        talloc_free(discard_const(debug_prg_name));
+        goto fail;
+    }
+    talloc_steal(main_ctx, debug_prg_name);
+
+    buf = talloc_size(main_ctx, sizeof(uint8_t)*IN_BUF_SIZE);
+    if (buf == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "talloc_size failed.\n");
+        goto fail;
+    }
+
+    ibuf = talloc_zero(main_ctx, struct input_buffer);
+    if (ibuf == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "talloc_zero failed.\n");
+        goto fail;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, "context initialized\n");
+
+    errno = 0;
+    len = sss_atomic_read_s(STDIN_FILENO, buf, IN_BUF_SIZE);
+    if (len == -1) {
+        ret = errno;
+        DEBUG(SSSDBG_CRIT_FAILURE, "read failed [%d][%s].\n", ret, strerror(ret));
+        goto fail;
+    }
+
+    close(STDIN_FILENO);
+
+    ret = unpack_buffer(buf, len, ibuf);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_CRIT_FAILURE,
+              "unpack_buffer failed.[%d][%s].\n", ret, strerror(ret));
+        goto fail;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, "performing selinux operations\n");
+
+    ret = set_seuser(ibuf->username, ibuf->seuser, ibuf->mls_range);
+
+    ret = prepare_response(main_ctx, ret, &resp);
+
+    errno = 0;
+
+    written = sss_atomic_write_s(STDOUT_FILENO, resp->buf, resp->size);
+    if (written == -1) {
+        ret = errno;
+        DEBUG(SSSDBG_CRIT_FAILURE, "write failed [%d][%s].\n", ret,
+                    strerror(ret));
+        goto fail;
+    }
+
+    if (written != resp->size) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "Expected to write %zu bytes, wrote %zu\n",
+              resp->size, written);
+        goto fail;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, "selinux_child completed successfully\n");
+    close(STDOUT_FILENO);
+    talloc_free(main_ctx);
+    return EXIT_SUCCESS;
+fail:
+    DEBUG(SSSDBG_CRIT_FAILURE, "selinux_child failed!\n");
+    close(STDOUT_FILENO);
+    talloc_free(main_ctx);
+    return EXIT_FAILURE;
+}