coredump: drop caps while we are processing the coredump

https://bugs.freedesktop.org/show_bug.cgi?id=87354

1 files changed, 16 insertions, 14 deletions

diff --git a/src/shared/capability.c b/src/shared/capability.c
index b1be04380..b39e8e235 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)