X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=blobdiff_plain;f=src%2Fbin%2Flttng-sessiond%2Fshm.c;h=23bd9db2085221f341454bee136c76b1a6b91c68;hp=b94f4eb6a7aae86aed5fc080689e3f755456c719;hb=e6852848914f842a703ea4d35172297ccd066589;hpb=0525e9ae15d215943d8187e7f190d5a45e723085

diff --git a/src/bin/lttng-sessiond/shm.c b/src/bin/lttng-sessiond/shm.c
index b94f4eb6a..23bd9db20 100644
--- a/src/bin/lttng-sessiond/shm.c
+++ b/src/bin/lttng-sessiond/shm.c
@@ -16,7 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#define _GNU_SOURCE
+#define _LGPL_SOURCE
 #include <fcntl.h>
 #include <limits.h>
 #include <sys/mman.h>
@@ -48,40 +48,17 @@ static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
 	/* Default permissions */
 	mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
 
-	/* Change owner of the shm path */
+	/*
+	 * Change owner of the shm path.
+	 */
 	if (global) {
-		ret = chown(shm_path, 0, 0);
-		if (ret < 0) {
-			if (errno != ENOENT) {
-				PERROR("chown wait shm");
-				goto error;
-			}
-		}
-
 		/*
-		 * If global session daemon, any application can register so the shm
-		 * needs to be set in read-only mode for others.
+		 * If global session daemon, any application can
+		 * register. Make it initially writeable so applications
+		 * registering concurrently can do ftruncate() by
+		 * themselves.
 		 */
-		mode |= S_IROTH;
-	} else {
-		ret = chown(shm_path, getuid(), getgid());
-		if (ret < 0) {
-			if (errno != ENOENT) {
-				PERROR("chown wait shm");
-				goto error;
-			}
-		}
-	}
-
-	/*
-	 * Set permissions to the shm even if we did not create the shm.
-	 */
-	ret = chmod(shm_path, mode);
-	if (ret < 0) {
-		if (errno != ENOENT) {
-			PERROR("chmod wait shm");
-			goto error;
-		}
+		mode |= S_IROTH | S_IWOTH;
 	}
 
 	/*
@@ -96,7 +73,7 @@ static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
 	 */
 	wait_shm_fd = shm_open(shm_path, O_RDWR | O_CREAT, mode);
 	if (wait_shm_fd < 0) {
-		PERROR("shm_open wait shm");
+		PERROR("Failed to open wait shm at %s", shm_path);
 		goto error;
 	}
 
@@ -107,13 +84,32 @@ static int get_wait_shm(char *shm_path, size_t mmap_size, int global)
 	}
 
 #ifndef __FreeBSD__
-	ret = fchmod(wait_shm_fd, mode);
-	if (ret < 0) {
-		PERROR("fchmod");
-		exit(EXIT_FAILURE);
+	if (global) {
+		ret = fchown(wait_shm_fd, 0, 0);
+		if (ret < 0) {
+			PERROR("fchown");
+			exit(EXIT_FAILURE);
+		}
+		/*
+		 * If global session daemon, any application can
+		 * register so the shm needs to be set in read-only mode
+		 * for others.
+		 */
+		mode &= ~S_IWOTH;
+		ret = fchmod(wait_shm_fd, mode);
+		if (ret < 0) {
+			PERROR("fchmod");
+			exit(EXIT_FAILURE);
+		}
+	} else {
+		ret = fchown(wait_shm_fd, getuid(), getgid());
+		if (ret < 0) {
+			PERROR("fchown");
+			exit(EXIT_FAILURE);
+		}
 	}
 #else
-#warning "FreeBSD does not support setting file mode on shm FD. Remember that for secure use, lttng-sessiond should be started before applications linked on lttng-ust."
+#warning "FreeBSD does not support setting file mode on shm FD."
 #endif
 
 	DBG("Got the wait shm fd %d", wait_shm_fd);
@@ -136,12 +132,20 @@ error:
  */
 char *shm_ust_get_mmap(char *shm_path, int global)
 {
-	size_t mmap_size = sysconf(_SC_PAGE_SIZE);
+	size_t mmap_size;
 	int wait_shm_fd, ret;
 	char *wait_shm_mmap;
+	long sys_page_size;
 
 	assert(shm_path);
 
+	sys_page_size = sysconf(_SC_PAGE_SIZE);
+	if (sys_page_size < 0) {
+		PERROR("sysconf PAGE_SIZE");
+		goto error;
+	}
+	mmap_size = sys_page_size;
+
 	wait_shm_fd = get_wait_shm(shm_path, mmap_size, global);
 	if (wait_shm_fd < 0) {
 		goto error;