From f11943c53ec181829a821c6b27acf828bab71caa Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Thu, 29 Jan 2015 02:47:29 +0100
Subject: [PATCH] coredump: drop caps while we are processing the coredump

https://bugs.freedesktop.org/show_bug.cgi?id=87354
---
 src/journal/coredump.c  | 21 +++++++++++----------
 src/shared/capability.c | 30 ++++++++++++++++--------------
 2 files changed, 27 insertions(+), 24 deletions(-)

diff --git a/src/journal/coredump.c b/src/journal/coredump.c
index d322e7984c5..f6b95145d20 100644
--- a/src/journal/coredump.c
+++ b/src/journal/coredump.c
@@ -31,9 +31,8 @@
 #  include <elfutils/libdwfl.h>
 #endif
 
-#include "systemd/sd-journal.h"
-#include "systemd/sd-login.h"
-
+#include "sd-journal.h"
+#include "sd-login.h"
 #include "log.h"
 #include "util.h"
 #include "fileio.h"
@@ -42,14 +41,15 @@
 #include "mkdir.h"
 #include "special.h"
 #include "cgroup-util.h"
-#include "journald-native.h"
 #include "conf-parser.h"
 #include "copy.h"
 #include "stacktrace.h"
 #include "path-util.h"
 #include "compress.h"
-#include "coredump-vacuum.h"
 #include "acl-util.h"
+#include "capability.h"
+#include "journald-native.h"
+#include "coredump-vacuum.h"
 
 /* The maximum size up to which we process coredumps */
 #define PROCESS_SIZE_MAX ((off_t) (2LLU*1024LLU*1024LLU*1024LLU))
@@ -810,11 +810,12 @@ int main(int argc, char* argv[]) {
          * segfaulted process and allocate the coredump memory under
          * the user's uid. This also ensures that the credentials
          * journald will see are the ones of the coredumping user,
-         * thus making sure the user gets access to the core dump. */
-        if (setresgid(gid, gid, gid) < 0 ||
-            setresuid(uid, uid, uid) < 0) {
-                log_error_errno(errno, "Failed to drop privileges: %m");
-                r = -errno;
+         * thus making sure the user gets access to the core
+         * dump. Let's also get rid of all capabilities, if we run as
+         * root, we won't need them anymore. */
+        r = drop_privileges(uid, gid, 0);
+        if (r < 0) {
+                log_error_errno(r, "Failed to drop privileges: %m");
                 goto finish;
         }
 
diff --git a/src/shared/capability.c b/src/shared/capability.c
index b1be0438037..b39e8e2359d 100644
--- a/src/shared/capability.c
+++ b/src/shared/capability.c
@@ -230,8 +230,9 @@ int capability_bounding_set_drop_usermode(uint64_t drop) {
 }
 
 int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
-
+        cap_value_t bits[sizeof(keep_capabilities)*8];
         _cleanup_cap_free_ cap_t d = NULL;
+        unsigned i, j = 0;
         int r;
 
         /* Unfortunately we cannot leave privilege dropping to PID 1
@@ -247,7 +248,8 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
         if (setgroups(0, NULL) < 0)
                 return log_error_errno(errno, "Failed to drop auxiliary groups list: %m");
 
-        if (prctl(PR_SET_KEEPCAPS, 1) < 0)
+        /* Ensure we keep the permitted caps across the setresuid(), if we need them */
+        if (prctl(PR_SET_KEEPCAPS, keep_capabilities != 0) < 0)
                 return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
 
         r = setresuid(uid, uid, uid);
@@ -257,27 +259,27 @@ int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
         if (prctl(PR_SET_KEEPCAPS, 0) < 0)
                 return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
 
+        /* Drop all caps from the bounding set, except the ones we want */
         r = capability_bounding_set_drop(~keep_capabilities, true);
         if (r < 0)
                 return log_error_errno(r, "Failed to drop capabilities: %m");
 
+        if (keep_capabilities == 0) /* All is gone, we can exit early */
+                return 0;
+
+        /* Now upgrade the permitted caps we still kept to effective caps */
         d = cap_init();
         if (!d)
                 return log_oom();
 
-        if (keep_capabilities) {
-                cap_value_t bits[sizeof(keep_capabilities)*8];
-                unsigned i, j = 0;
+        for (i = 0; i < sizeof(keep_capabilities)*8; i++)
+                if (keep_capabilities & (1ULL << i))
+                        bits[j++] = i;
 
-                for (i = 0; i < sizeof(keep_capabilities)*8; i++)
-                        if (keep_capabilities & (1ULL << i))
-                                bits[j++] = i;
-
-                if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
-                    cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) {
-                        log_error_errno(errno, "Failed to enable capabilities bits: %m");
-                        return -errno;
-                }
+        if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
+            cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0) {
+                log_error_errno(errno, "Failed to enable capabilities bits: %m");
+                return -errno;
         }
 
         if (cap_set_proc(d) < 0)