6.15-stable review patch. If anyone has any objections, please let me know.
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From: Al Viro viro@zeniv.linux.org.uk
[ Upstream commit 532c8b51b3a8676cbf533a291f8156774f30ea87 ]
[dma_buf_fd() fixes; no preferences regarding the tree it goes through - up to xen folks]
As soon as we'd inserted a file reference into descriptor table, another thread could close it. That's fine for the case when all we are doing is returning that descriptor to userland (it's a race, but it's a userland race and there's nothing the kernel can do about it). However, if we follow fd_install() with any kind of access to objects that would be destroyed on close (be it the struct file itself or anything destroyed by its ->release()), we have a UAF.
dma_buf_fd() is a combination of reserving a descriptor and fd_install(). gntdev dmabuf_exp_from_pages() calls it and then proceeds to access the objects destroyed on close - starting with gntdev_dmabuf itself.
Fix that by doing reserving descriptor before anything else and do fd_install() only when everything had been set up.
Fixes: a240d6e42e28 ("xen/gntdev: Implement dma-buf export functionality") Signed-off-by: Al Viro viro@zeniv.linux.org.uk Acked-by: Juergen Gross jgross@suse.com Message-ID: 20250712050916.GY1880847@ZenIV Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/xen/gntdev-dmabuf.c | 28 ++++++++++------------------ 1 file changed, 10 insertions(+), 18 deletions(-)
diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c index 5453d86324f6..82855105ab85 100644 --- a/drivers/xen/gntdev-dmabuf.c +++ b/drivers/xen/gntdev-dmabuf.c @@ -357,8 +357,11 @@ struct gntdev_dmabuf_export_args { static int dmabuf_exp_from_pages(struct gntdev_dmabuf_export_args *args) { DEFINE_DMA_BUF_EXPORT_INFO(exp_info); - struct gntdev_dmabuf *gntdev_dmabuf; - int ret; + struct gntdev_dmabuf *gntdev_dmabuf __free(kfree) = NULL; + CLASS(get_unused_fd, ret)(O_CLOEXEC); + + if (ret < 0) + return ret;
gntdev_dmabuf = kzalloc(sizeof(*gntdev_dmabuf), GFP_KERNEL); if (!gntdev_dmabuf) @@ -383,32 +386,21 @@ static int dmabuf_exp_from_pages(struct gntdev_dmabuf_export_args *args) exp_info.priv = gntdev_dmabuf;
gntdev_dmabuf->dmabuf = dma_buf_export(&exp_info); - if (IS_ERR(gntdev_dmabuf->dmabuf)) { - ret = PTR_ERR(gntdev_dmabuf->dmabuf); - gntdev_dmabuf->dmabuf = NULL; - goto fail; - } - - ret = dma_buf_fd(gntdev_dmabuf->dmabuf, O_CLOEXEC); - if (ret < 0) - goto fail; + if (IS_ERR(gntdev_dmabuf->dmabuf)) + return PTR_ERR(gntdev_dmabuf->dmabuf);
gntdev_dmabuf->fd = ret; args->fd = ret;
pr_debug("Exporting DMA buffer with fd %d\n", ret);
+ get_file(gntdev_dmabuf->priv->filp); mutex_lock(&args->dmabuf_priv->lock); list_add(&gntdev_dmabuf->next, &args->dmabuf_priv->exp_list); mutex_unlock(&args->dmabuf_priv->lock); - get_file(gntdev_dmabuf->priv->filp); - return 0;
-fail: - if (gntdev_dmabuf->dmabuf) - dma_buf_put(gntdev_dmabuf->dmabuf); - kfree(gntdev_dmabuf); - return ret; + fd_install(take_fd(ret), no_free_ptr(gntdev_dmabuf)->dmabuf->file); + return 0; }
static struct gntdev_grant_map *