[Mesa-dev] [PATCH] Call shmget() with permission 0600 instead of 0777

[Brian Paul]

A security advisory (TALOS-2019-0857/CVE-2019-5068) found that
creating shared memory regions with permission mode 0777 could allow
any user to access that memory.  Several Mesa drivers use shared-
memory XImages to implement back buffers for improved performance.

This path changes the shmget() calls to use 0600 (user r/w).

Tested with legacy Xlib driver and llvmpipe.

Cc: mesa-stable at lists.freedesktop.org
---
 src/gallium/winsys/sw/dri/dri_sw_winsys.c   | 3 ++-
 src/gallium/winsys/sw/xlib/xlib_sw_winsys.c | 3 ++-
 src/mesa/drivers/x11/xm_buffer.c            | 3 ++-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/gallium/winsys/sw/dri/dri_sw_winsys.c b/src/gallium/winsys/sw/dri/dri_sw_winsys.c
index 761f5d1..2e5970b 100644
--- a/src/gallium/winsys/sw/dri/dri_sw_winsys.c
+++ b/src/gallium/winsys/sw/dri/dri_sw_winsys.c
@@ -92,7 +92,8 @@ alloc_shm(struct dri_sw_displaytarget *dri_sw_dt, unsigned size)
 {
    char *addr;
 
-   dri_sw_dt->shmid = shmget(IPC_PRIVATE, size, IPC_CREAT|0777);
+   /* 0600 = user read+write */
+   dri_sw_dt->shmid = shmget(IPC_PRIVATE, size, IPC_CREAT | 0600);
    if (dri_sw_dt->shmid < 0)
       return NULL;
 
diff --git a/src/gallium/winsys/sw/xlib/xlib_sw_winsys.c b/src/gallium/winsys/sw/xlib/xlib_sw_winsys.c
index c14c9de..edebb48 100644
--- a/src/gallium/winsys/sw/xlib/xlib_sw_winsys.c
+++ b/src/gallium/winsys/sw/xlib/xlib_sw_winsys.c
@@ -126,7 +126,8 @@ alloc_shm(struct xlib_displaytarget *buf, unsigned size)
    shminfo->shmid = -1;
    shminfo->shmaddr = (char *) -1;
 
-   shminfo->shmid = shmget(IPC_PRIVATE, size, IPC_CREAT|0777);
+   /* 0600 = user read+write */
+   shminfo->shmid = shmget(IPC_PRIVATE, size, IPC_CREAT | 0600);
    if (shminfo->shmid < 0) {
       return NULL;
    }
diff --git a/src/mesa/drivers/x11/xm_buffer.c b/src/mesa/drivers/x11/xm_buffer.c
index d945d8a..0da08a6 100644
--- a/src/mesa/drivers/x11/xm_buffer.c
+++ b/src/mesa/drivers/x11/xm_buffer.c
@@ -89,8 +89,9 @@ alloc_back_shm_ximage(XMesaBuffer b, GLuint width, GLuint height)
       return GL_FALSE;
    }
 
+   /* 0600 = user read+write */
    b->shminfo.shmid = shmget(IPC_PRIVATE, b->backxrb->ximage->bytes_per_line
-			     * b->backxrb->ximage->height, IPC_CREAT|0777);
+                             * b->backxrb->ximage->height, IPC_CREAT | 0600);
    if (b->shminfo.shmid < 0) {
       _mesa_warning(NULL, "shmget failed while allocating back buffer.\n");
       XDestroyImage(b->backxrb->ximage);
-- 
1.8.5.6