coredump,catalog: give better notice when a core file is truncated

coredump had code to check if copy_bytes() hit the max_bytes limit,
and refuse further processing in that case.
But in 84ee096044, the return convention for copy_bytes() was changed
from -EFBIG to 1 for the case when the limit is hit, so the condition
check in coredump couldn't ever trigger.
But it seems that *do* want to process such truncated cores [1].
So change the code to detect truncation properly, but instead of
returning an error, give a nice log entry.

[1] https://github.com/systemd/systemd/issues/3883#issuecomment-239106337

Should fix (or at least alleviate) #3883.

TODO

@@ -670,6 +670,7 @@ Features:
 
 * coredump:
   - save coredump in Windows/Mozilla minidump format
+  - when truncating coredumps, also log the full size that the process had, and make a metadata field so we can report truncated coredumps
 
 * support crash reporting operation modes (https://live.gnome.org/GnomeOS/Design/Whiteboards/ProblemReporting)
 

catalog/systemd.catalog.in

@@ -88,6 +88,17 @@ Process @COREDUMP_PID@ (@COREDUMP_COMM@) crashed and dumped core.
 This usually indicates a programming error in the crashing program and
 should be reported to its vendor as a bug.
 
+-- 5aadd8e954dc4b1a8c954d63fd9e1137
+Subject: Core file was truncated to @SIZE_LIMIT@ bytes.
+Defined-By: systemd
+Support: %SUPPORT_URL%
+Documentation: man:coredump.conf(5)
+
+The process had more memory mapped than the configured maximum for processing
+and storage by systemd-coredump(8). Only the first @SIZE_LIMIT@ bytes were
+saved. This core might still be usable, but various tools like gdb(1) will warn
+about the file being truncated.
+
 -- fc2e22bc6ee647b6b90729ab34a250b1 de
 Subject: Speicherabbild für Prozess @COREDUMP_PID@ (@COREDUMP_COMM) generiert
 Defined-By: systemd

src/coredump/coredump.c

@@ -28,9 +28,10 @@
 #include <elfutils/libdwfl.h>
 #endif
 
+#include "sd-daemon.h"
 #include "sd-journal.h"
 #include "sd-login.h"
-#include "sd-daemon.h"
+#include "sd-messages.h"
 
 #include "acl-util.h"
 #include "alloc-util.h"
@@ -133,6 +134,10 @@ static int parse_config(void) {
                                  false, NULL);
 }
 
+static inline uint64_t storage_size_max(void) {
+        return arg_storage == COREDUMP_STORAGE_EXTERNAL ? arg_external_size_max : arg_journal_size_max;
+}
+
 static int fix_acl(int fd, uid_t uid) {
 
 #ifdef HAVE_ACL
@@ -329,12 +334,13 @@ static int save_external_coredump(
                 /* Is coredumping disabled? Then don't bother saving/processing the coredump.
                  * Anything below PAGE_SIZE cannot give a readable coredump (the kernel uses
                  * ELF_EXEC_PAGESIZE which is not easily accessible, but is usually the same as PAGE_SIZE. */
-                log_info("Core dumping has been disabled for process %s (%s).", context[CONTEXT_PID], context[CONTEXT_COMM]);
+                log_info("Resource limits disable core dumping for process %s (%s).",
+                         context[CONTEXT_PID], context[CONTEXT_COMM]);
                 return -EBADSLT;
         }
 
         /* Never store more than the process configured, or than we actually shall keep or process */
-        max_size = MIN(rlimit, MAX(arg_process_size_max, arg_external_size_max));
+        max_size = MIN(rlimit, MAX(arg_process_size_max, storage_size_max()));
 
         r = make_filename(context, &fn);
         if (r < 0)
@@ -347,19 +353,18 @@ static int save_external_coredump(
                 return log_error_errno(fd, "Failed to create temporary file for coredump %s: %m", fn);
 
         r = copy_bytes(input_fd, fd, max_size, false);
-        if (r == -EFBIG) {
-                log_error("Coredump of %s (%s) is larger than configured processing limit, refusing.", context[CONTEXT_PID], context[CONTEXT_COMM]);
+        if (r < 0) {
+                log_error_errno(r, "Cannot store coredump of %s (%s): %m", context[CONTEXT_PID], context[CONTEXT_COMM]);
                 goto fail;
-        } else if (IN_SET(r, -EDQUOT, -ENOSPC)) {
-                log_error("Not enough disk space for coredump of %s (%s), refusing.", context[CONTEXT_PID], context[CONTEXT_COMM]);
-                goto fail;
-        } else if (r < 0) {
-                log_error_errno(r, "Failed to dump coredump to file: %m");
-                goto fail;
-        }
+        } else if (r == 1)
+                log_struct(LOG_INFO,
+                           LOG_MESSAGE("Core file was truncated to %zu bytes.", max_size),
+                           "SIZE_LIMIT=%zu", max_size,
+                           LOG_MESSAGE_ID(SD_MESSAGE_TRUNCATED_CORE),
+                           NULL);
 
         if (fstat(fd, &st) < 0) {
-                log_error_errno(errno, "Failed to fstat coredump %s: %m", coredump_tmpfile_name(tmp));
+                log_error_errno(errno, "Failed to fstat core file %s: %m", coredump_tmpfile_name(tmp));
                 goto fail;
         }
 

src/systemd/sd-messages.h

@@ -40,6 +40,7 @@ _SD_BEGIN_DECLARATIONS;
 #define SD_MESSAGE_JOURNAL_USAGE    SD_ID128_MAKE(ec,38,7f,57,7b,84,4b,8f,a9,48,f3,3c,ad,9a,75,e6)
 
 #define SD_MESSAGE_COREDUMP         SD_ID128_MAKE(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1)
+#define SD_MESSAGE_TRUNCATED_CORE   SD_ID128_MAKE(5a,ad,d8,e9,54,dc,4b,1a,8c,95,4d,63,fd,9e,11,37)
 
 #define SD_MESSAGE_SESSION_START    SD_ID128_MAKE(8d,45,62,0c,1a,43,48,db,b1,74,10,da,57,c6,0c,66)
 #define SD_MESSAGE_SESSION_STOP     SD_ID128_MAKE(33,54,93,94,24,b4,45,6d,98,02,ca,83,33,ed,42,4a)