logging: allow max_len=0 to disable log rollover

Currently setting max_len=0 causes virtlogd to spin in a busy loop. It
is natural to allow this to disable log rollover which can be useful for
developers debugging things.

Note disabling rollover exposes the host to denial of service from a
malicious guest, so must be used with care.

Closes https://gitlab.com/libvirt/libvirt/-/issues/85
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

diff --git a/src/logging/virtlogd.conf b/src/logging/virtlogd.conf
index 8b1ff0156f1e9ed297a2389c23e48f11779e6f43..c53a1112bdb0110ac3e130989934916e16a981f5 100644 (file)
--- a/src/logging/virtlogd.conf
+++ b/src/logging/virtlogd.conf
@@ -87,6 +87,10 @@
 
 # Maximum file size before rolling over. Defaults to 2 MB
 #
+# Setting max_size to zero will disable rollover entirely.
+# NOTE: disabling rollover exposes the host filesystem to
+# denial of service from a malicious guest.
+#
 # Beware that a logrotate config file might be installed too,
 # to handle cases where virtlogd is disabled. To ensure that
 # the logrotate config is a no-op when virtlogd is running,

diff --git a/src/util/virrotatingfile.c b/src/util/virrotatingfile.c
index a88c332cf4d6a3dca4aac2bb798b7778acd43ef4..9f1ef17c3e14cc132eff4f21e10aaa4b9eb09494 100644 (file)
--- a/src/util/virrotatingfile.c
+++ b/src/util/virrotatingfile.c
@@ -225,7 +225,8 @@ virRotatingFileWriterDelete(virRotatingFileWriterPtr file)
  *
  * The files will never exceed @maxlen bytes in size,
  * but may be rolled over before they reach this size
- * in order to avoid splitting lines
+ * in order to avoid splitting lines. If @maxlen is
+ * zero then no rollover will be performed.
  */
 virRotatingFileWriterPtr
 virRotatingFileWriterNew(const char *path,
@@ -430,25 +431,27 @@ virRotatingFileWriterAppend(virRotatingFileWriterPtr file,
         size_t towrite = len;
         bool forceRollover = false;
 
-        if (file->entry->pos > file->maxlen) {
-            /* If existing file is for some reason larger then max length we
-             * won't write to this file anymore, but we rollover this file.*/
-            forceRollover = true;
-            towrite = 0;
-        } else if ((file->entry->pos + towrite) > file->maxlen) {
-            towrite = file->maxlen - file->entry->pos;
-
-            /*
-             * If there's a newline in the last 80 chars
-             * we're about to write, then break at that
-             * point to avoid splitting lines across
-             * separate files
-             */
-            for (i = 0; i < towrite && i < 80; i++) {
-                if (buf[towrite - i - 1] == '\n') {
-                    towrite -= i;
-                    forceRollover = true;
-                    break;
+        if (file->maxlen != 0) {
+            if (file->entry->pos > file->maxlen) {
+                /* If existing file is for some reason larger then max length we
+                 * won't write to this file anymore, but we rollover this file.*/
+                forceRollover = true;
+                towrite = 0;
+            } else if ((file->entry->pos + towrite) > file->maxlen) {
+                towrite = file->maxlen - file->entry->pos;
+
+                /*
+                 * If there's a newline in the last 80 chars
+                 * we're about to write, then break at that
+                 * point to avoid splitting lines across
+                 * separate files
+                 */
+                for (i = 0; i < towrite && i < 80; i++) {
+                    if (buf[towrite - i - 1] == '\n') {
+                        towrite -= i;
+                        forceRollover = true;
+                        break;
+                    }
                 }
             }
         }
@@ -468,8 +471,9 @@ virRotatingFileWriterAppend(virRotatingFileWriterPtr file,
             file->entry->len += towrite;
         }
 
-        if ((file->entry->pos == file->maxlen && len) ||
-            forceRollover) {
+        if (file->maxlen != 0 &&
+            ((file->entry->pos == file->maxlen && len) ||
+             forceRollover)) {
             virRotatingFileWriterEntryPtr tmp;
             VIR_DEBUG("Hit max size %zu on %s (force=%d)",
                       file->maxlen, file->basepath, forceRollover);