random-seed: provide nicer error message when unable to open file

If /var is read-only, and the seed file does not exist, we would print
a misleading error message for ENOENT. Print both messages instead, to
make it easy to diagonose.

Also, treat the cases of missing seed file the same as empty seed file
and exit successfully. Initialize the return code properly.

Fixes https://github.com/systemd/systemd/issues/2530,
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=813599.

1 files changed, 16 insertions, 6 deletions

diff --git a/src/random-seed/random-seed.c b/src/random-seed/random-seed.c
index d857ade36a..0041258d41 100644
--- a/src/random-seed/random-seed.c
+++ b/src/random-seed/random-seed.c
@@ -40,7 +40,7 @@ int main(int argc, char *argv[]) {
         _cleanup_free_ void* buf = NULL;
         size_t buf_size = 0;
         ssize_t k;
-        int r;
+        int r, open_rw_error;
         FILE *f;
         bool refresh_seed_file = true;
 
@@ -87,14 +87,23 @@ int main(int argc, char *argv[]) {
         if (streq(argv[1], "load")) {
 
                 seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
+                open_rw_error = -errno;
                 if (seed_fd < 0) {
+                        refresh_seed_file = false;
+
                         seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY);
                         if (seed_fd < 0) {
-                                r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
+                                bool missing = errno == ENOENT;
+
+                                log_full_errno(missing ? LOG_DEBUG : LOG_ERR,
+                                               open_rw_error, "Failed to open " RANDOM_SEED " for writing: %m");
+                                r = log_full_errno(missing ? LOG_DEBUG : LOG_ERR,
+                                                   errno, "Failed to open " RANDOM_SEED " for reading: %m");
+                                if (missing)
+                                        r = 0;
+
                                 goto finish;
                         }
-
-                        refresh_seed_file = false;
                 }
 
                 random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600);
@@ -109,9 +118,10 @@ int main(int argc, char *argv[]) {
                 k = loop_read(seed_fd, buf, buf_size, false);
                 if (k < 0)
                         r = log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m");
-                else if (k == 0)
+                else if (k == 0) {
+                        r = 0;
                         log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding.");
-                else {
+                } else {
                         (void) lseek(seed_fd, 0, SEEK_SET);
 
                         r = loop_write(random_fd, buf, (size_t) k, false);