Fix: incorrect close of fd 0 for syscall kernel event destroy

[lttng-tools.git] / src / bin / lttng-sessiond / kernel.c

diff --git a/src/bin/lttng-sessiond/kernel.c b/src/bin/lttng-sessiond/kernel.c
index d9e047fc3f5cdcc50a72ea68d0a7f29fa49b159b..2936406d84f704d1a293e95dd21f248e5c5660b3 100644 (file)
--- a/src/bin/lttng-sessiond/kernel.c
+++ b/src/bin/lttng-sessiond/kernel.c
@@ -204,12 +204,16 @@ int kernel_create_event(struct lttng_event *ev,
        }
 
        /*
-        * LTTNG_KERNEL_SYSCALL event creation will return 0 on success. However
-        * this FD must not be added to the event list.
+        * LTTNG_KERNEL_SYSCALL event creation will return 0 on success.
         */
        if (ret == 0 && event->event->instrumentation == LTTNG_KERNEL_SYSCALL) {
                DBG2("Kernel event syscall creation success");
-               goto end;
+               /*
+                * We use fd == -1 to ensure that we never trigger a close of fd
+                * 0.
+                */
+               event->fd = -1;
+               goto add_list;
        }
 
        event->fd = ret;
@@ -219,13 +223,13 @@ int kernel_create_event(struct lttng_event *ev,
                perror("fcntl session fd");
        }
 
+add_list:
        /* Add event to event list */
        cds_list_add(&event->list, &channel->events_list.head);
        channel->event_count++;
 
        DBG("Event %s created (fd: %d)", ev->name, event->fd);
 
-end:
        return 0;
 
 free_event:
@@ -484,7 +488,7 @@ int kernel_open_channel_stream(struct ltt_kernel_channel *channel)
        int ret;
        struct ltt_kernel_stream *lks;
 
-       while ((ret = kernctl_create_stream(channel->fd)) > 0) {
+       while ((ret = kernctl_create_stream(channel->fd)) >= 0) {
                lks = trace_kernel_create_stream();
                if (lks == NULL) {
                        close(ret);
@@ -623,18 +627,50 @@ int kernel_validate_version(int tracer_fd)
        }
 
        /* Validate version */
-       if (version.version > KERN_MODULES_VERSION) {
+       if (version.major != KERN_MODULES_PRE_MAJOR
+               && version.major != KERN_MODULES_MAJOR) {
                goto error_version;
        }
 
-       DBG2("Kernel tracer version validated (major version %d)", version.version);
+       DBG2("Kernel tracer version validated (major version %d)", version.major);
        return 0;
 
 error_version:
        ERR("Kernel major version %d is not compatible (supporting <= %d)",
-                       version.version, KERN_MODULES_VERSION)
+                       version.major, KERN_MODULES_MAJOR)
        ret = -1;
 
 error:
        return ret;
 }
+
+/*
+ * Kernel work-arounds called at the start of sessiond main().
+ */
+int init_kernel_workarounds(void)
+{
+       int ret;
+       FILE *fp;
+
+       /*
+        * boot_id needs to be read once before being used concurrently
+        * to deal with a Linux kernel race. A fix is proposed for
+        * upstream, but the work-around is needed for older kernels.
+        */
+       fp = fopen("/proc/sys/kernel/random/boot_id", "r");
+       if (!fp) {
+               goto end_boot_id;
+       }
+       while (!feof(fp)) {
+               char buf[37] = "";
+
+               ret = fread(buf, 1, sizeof(buf), fp);
+               if (ret < 0) {
+                       /* Ignore error, we don't really care */
+               }
+       }
+       fclose(fp);
+end_boot_id:
+
+       return 0;
+}