journal: refuse opening journal files from the future for writing

Never permit that we write to journal files that have newer timestamps than our
local wallclock has. If we'd accept that, then the entries in the file might
end up not being ordered strictly.

Let's refuse this with ETXTBSY, and then immediately rotate to use a new file,
so that each file remains strictly ordered also be wallclock internally.

2 files changed, 23 insertions, 2 deletions

diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
index e26c8223d8..49199b269f 100644
--- a/src/journal/journal-file.c
+++ b/src/journal/journal-file.c
@@ -568,8 +568,8 @@ static int journal_file_verify_header(JournalFile *f) {
                 return -ENODATA;
 
         if (f->writable) {
-                uint8_t state;
                 sd_id128_t machine_id;
+                uint8_t state;
                 int r;
 
                 r = sd_id128_get_machine(&machine_id);
@@ -590,6 +590,14 @@ static int journal_file_verify_header(JournalFile *f) {
                         log_debug("Journal file %s has unknown state %i.", f->path, state);
                         return -EBUSY;
                 }
+
+                /* Don't permit appending to files from the future. Because otherwise the realtime timestamps wouldn't
+                 * be strictly ordered in the entries in the file anymore, and we can't have that since it breaks
+                 * bisection. */
+                if (le64toh(f->header->tail_entry_realtime) > now(CLOCK_REALTIME)) {
+                        log_debug("Journal file %s is from the future, refusing to append new data to it that'd be older.", f->path);
+                        return -ETXTBSY;
+                }
         }
 
         f->compress_xz = JOURNAL_HEADER_COMPRESSED_XZ(f->header);
@@ -3330,7 +3338,8 @@ int journal_file_open_reliably(
                     -EBUSY,             /* unclean shutdown */
                     -ESHUTDOWN,         /* already archived */
                     -EIO,               /* IO error, including SIGBUS on mmap */
-                    -EIDRM              /* File has been deleted */))
+                    -EIDRM,             /* File has been deleted */
+                    -ETXTBSY))          /* File is from the future */
                 return r;
 
         if ((flags & O_ACCMODE) == O_RDONLY)
diff --git a/src/journal/journald-server.c b/src/journal/journald-server.c
index 28aea35d18..3224bdbf5f 100644
--- a/src/journal/journald-server.c
+++ b/src/journal/journald-server.c
@@ -595,32 +595,44 @@ static void server_cache_hostname(Server *s) {
 
 static bool shall_try_append_again(JournalFile *f, int r) {
         switch(r) {
+
         case -E2BIG:           /* Hit configured limit          */
         case -EFBIG:           /* Hit fs limit                  */
         case -EDQUOT:          /* Quota limit hit               */
         case -ENOSPC:          /* Disk full                     */
                 log_debug("%s: Allocation limit reached, rotating.", f->path);
                 return true;
+
         case -EIO:             /* I/O error of some kind (mmap) */
                 log_warning("%s: IO error, rotating.", f->path);
                 return true;
+
         case -EHOSTDOWN:       /* Other machine                 */
                 log_info("%s: Journal file from other machine, rotating.", f->path);
                 return true;
+
         case -EBUSY:           /* Unclean shutdown              */
                 log_info("%s: Unclean shutdown, rotating.", f->path);
                 return true;
+
         case -EPROTONOSUPPORT: /* Unsupported feature           */
                 log_info("%s: Unsupported feature, rotating.", f->path);
                 return true;
+
         case -EBADMSG:         /* Corrupted                     */
         case -ENODATA:         /* Truncated                     */
         case -ESHUTDOWN:       /* Already archived              */
                 log_warning("%s: Journal file corrupted, rotating.", f->path);
                 return true;
+
         case -EIDRM:           /* Journal file has been deleted */
                 log_warning("%s: Journal file has been deleted, rotating.", f->path);
                 return true;
+
+        case -ETXTBSY:         /* Journal file is from the future */
+                log_warning("%s: Journal file is from the future, rotateing.", f->path);
+                return true;
+
         default:
                 return false;
         }