[Nouveau] [PATCH v2] nouveau: dup fd before passing it to device

[Ilia Mirkin]

nouveau screens are reused for the same device node. However in the
scenario where we create screen 1, screen 2, and then delete screen 1,
the surrounding code might also close the original device node. To
protect against this, dup the fd and use the dup'd fd in the
nouveau_device. Also tell the nouveau_device that it is the owner of the
fd so that it will be closed on destruction.

Also make sure to free the nouveau_device in case of any failure.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=79823
Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
Cc: "10.2" <mesa-stable at lists.freedesktop.org>
---

v1 -> v2:
  clean up dup fd if device creation fails

 src/gallium/winsys/nouveau/drm/nouveau_drm_winsys.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/gallium/winsys/nouveau/drm/nouveau_drm_winsys.c b/src/gallium/winsys/nouveau/drm/nouveau_drm_winsys.c
index 1dfdaac..0635246 100644
--- a/src/gallium/winsys/nouveau/drm/nouveau_drm_winsys.c
+++ b/src/gallium/winsys/nouveau/drm/nouveau_drm_winsys.c
@@ -1,4 +1,5 @@
 #include <sys/stat.h>
+#include <unistd.h>
 #include "pipe/p_context.h"
 #include "pipe/p_state.h"
 #include "util/u_format.h"
@@ -59,7 +60,7 @@ nouveau_drm_screen_create(int fd)
 	struct nouveau_device *dev = NULL;
 	struct pipe_screen *(*init)(struct nouveau_device *);
 	struct nouveau_screen *screen;
-	int ret;
+	int ret, dupfd = -1;
 
 	pipe_mutex_lock(nouveau_screen_mutex);
 	if (!fd_tab) {
@@ -75,7 +76,17 @@ nouveau_drm_screen_create(int fd)
 		return &screen->base;
 	}
 
-	ret = nouveau_device_wrap(fd, 0, &dev);
+	/* Since the screen re-use is based on the device node and not the fd,
+	 * create a copy of the fd to be owned by the device. Otherwise a
+	 * scenario could occur where two screens are created, and the first
+	 * one is shut down, along with the fd being closed. The second
+	 * (identical) screen would now have a reference to the closed fd. We
+	 * avoid this by duplicating the original fd. Note that
+	 * nouveau_device_wrap does not close the fd in case of a device
+	 * creation error.
+	 */
+	dupfd = dup(fd);
+	ret = nouveau_device_wrap(dupfd, 1, &dev);
 	if (ret)
 		goto err;
 
@@ -115,6 +126,10 @@ nouveau_drm_screen_create(int fd)
 	return &screen->base;
 
 err:
+	if (dev)
+		nouveau_device_del(&dev);
+	else if (dupfd >= 0)
+		close(dupfd);
 	pipe_mutex_unlock(nouveau_screen_mutex);
 	return NULL;
 }
-- 
1.8.5.5