X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=libringbuffer%2Ffrontend_internal.h;h=2f837f7d80134449816afcb3e97546bd311aea0e;hb=refs%2Fheads%2Fstable-2.0;hp=6d1a75bdceef83e06d982097b94e4cdc8d8bcf59;hpb=e92f3e285939848f248af08f11a39a04a7fcf852;p=lttng-ust.git

diff --git a/libringbuffer/frontend_internal.h b/libringbuffer/frontend_internal.h
index 6d1a75bd..2f837f7d 100644
--- a/libringbuffer/frontend_internal.h
+++ b/libringbuffer/frontend_internal.h
@@ -32,6 +32,8 @@
  */
 
 #include <urcu/compiler.h>
+#include <signal.h>
+#include <pthread.h>
 
 #include <lttng/ringbuffer-config.h>
 #include "backend_types.h"
@@ -339,6 +341,12 @@ void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
 		 * The subbuffer size is least 2 bytes (minimum size: 1 page).
 		 * This guarantees that old_commit_count + 1 != commit_count.
 		 */
+
+		/*
+		 * Order prior updates to reserve count prior to the
+		 * commit_cold cc_sb update.
+		 */
+		cmm_smp_wmb();
 		if (caa_likely(v_cmpxchg(config, &shmp_index(handle, buf->commit_cold, idx)->cc_sb,
 					 old_commit_count, old_commit_count + 1)
 			   == old_commit_count)) {
@@ -384,6 +392,11 @@ void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
 			/* End of exclusive subbuffer access */
 			v_set(config, &shmp_index(handle, buf->commit_cold, idx)->cc_sb,
 			      commit_count);
+			/*
+			 * Order later updates to reserve count after
+			 * the commit cold cc_sb update.
+			 */
+			cmm_smp_wmb();
 			lib_ring_buffer_vmcore_check_deliver(config, buf,
 						 commit_count, idx, handle);
 
@@ -397,7 +410,9 @@ void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
 				int wakeup_fd = shm_get_wakeup_fd(handle, &buf->self._ref);
 
 				if (wakeup_fd >= 0) {
-					int ret;
+					sigset_t sigpipe_set, pending_set, old_set;
+					int ret, sigpipe_was_pending = 0;
+
 					/*
 					 * Wake-up the other end by
 					 * writing a null byte in the
@@ -416,13 +431,55 @@ void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config
 					 * 2) check if there is data in
 					 *    the buffer.
 					 * 3) wait on the pipe (poll).
+					 *
+					 * Discard the SIGPIPE from write(), not
+					 * disturbing any SIGPIPE that might be
+					 * already pending. If a bogus SIGPIPE
+					 * is sent to the entire process
+					 * concurrently by a malicious user, it
+					 * may be simply discarded.
 					 */
+					ret = sigemptyset(&pending_set);
+					assert(!ret);
+					/*
+					 * sigpending returns the mask
+					 * of signals that are _both_
+					 * blocked for the thread _and_
+					 * pending for either the thread
+					 * or the entire process.
+					 */
+					ret = sigpending(&pending_set);
+					assert(!ret);
+					sigpipe_was_pending = sigismember(&pending_set, SIGPIPE);
+					/*
+					 * If sigpipe was pending, it
+					 * means it was already blocked,
+					 * so no need to block it.
+					 */
+					if (!sigpipe_was_pending) {
+						ret = sigemptyset(&sigpipe_set);
+						assert(!ret);
+						ret = sigaddset(&sigpipe_set, SIGPIPE);
+						assert(!ret);
+						ret = pthread_sigmask(SIG_BLOCK, &sigpipe_set, &old_set);
+						assert(!ret);
+					}
 					do {
 						ret = write(wakeup_fd, "", 1);
 					} while (ret == -1L && errno == EINTR);
+					if (ret == -1L && errno == EPIPE && !sigpipe_was_pending) {
+						struct timespec timeout = { 0, 0 };
+						do {
+							ret = sigtimedwait(&sigpipe_set, NULL,
+								&timeout);
+						} while (ret == -1L && errno == EINTR);
+					}
+					if (!sigpipe_was_pending) {
+						ret = pthread_sigmask(SIG_SETMASK, &old_set, NULL);
+						assert(!ret);
+					}
 				}
 			}
-
 		}
 	}
 }