fix corrupt sysvipc timestamps on 32-bit archs with old kernels

kernel commit 4693916846269d633a3664586650dbfac2c5562f (first included
in release v4.14) silently fixed a bug whereby the reserved space
(which was later used for high bits of time) in IPC_STAT structures
was left untouched rather than zeroed. this means that a caller that
wants to read the high bits needs to pre-zero the memory.

since it's not clear that these operations are permitted to modify the
destination buffer on failure, use a temp buffer and copy back to the
caller's buffer on success.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/ipc/shmctl.c b/src/ipc/shmctl.c
index de3ce9d4..1c9f78c2 100644
--- a/src/ipc/shmctl.c
+++ b/src/ipc/shmctl.c
@@ -9,6 +9,14 @@
 
 int shmctl(int id, int cmd, struct shmid_ds *buf)
 {
+#if IPC_TIME64
+	struct shmid_ds out, *orig;
+	if (cmd&IPC_TIME64) {
+		out = (struct shmid_ds){0};
+		orig = buf;
+		buf = &out;
+	}
+#endif
 #ifdef SYSCALL_IPC_BROKEN_MODE
 	struct shmid_ds tmp;
 	if (cmd == IPC_SET) {
@@ -32,6 +40,8 @@ int shmctl(int id, int cmd, struct shmid_ds *buf)
 #endif
 #if IPC_TIME64
 	if (r >= 0 && (cmd&IPC_TIME64)) {
+		buf = orig;
+		*buf = out;
 		IPC_HILO(buf, shm_atime);
 		IPC_HILO(buf, shm_dtime);
 		IPC_HILO(buf, shm_ctime);