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Subject[PATCH] dma-buf: simplified calling conventions for dma_buf_fd()
Date
From: Al Viro <viro@zeniv.linux.org.uk>

Make dma_buf_fd() drop the file reference on failure, folding
dma_buf_put() into it.

Users of dma_buf_fd() (drm, videobuf2, ion and tee) are updated to take
the new calling convention into account.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[jw: rebased and updated commit message]
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
---

I received this patch as a response to what has become
bb765d1c331f ("tee: shm: fix use-after-free via temporarily dropped reference")

drivers/dma-buf/dma-buf.c | 16 +++++----
drivers/gpu/drm/drm_prime.c | 15 +++-----
drivers/gpu/drm/i915/gvt/dmabuf.c | 4 +--
drivers/gpu/drm/ttm/ttm_object.c | 3 +-
.../media/common/videobuf2/videobuf2-core.c | 14 ++++----
drivers/staging/android/ion/ion.c | 7 +---
drivers/tee/tee_core.c | 35 ++++++-------------
drivers/tee/tee_shm.c | 8 +----
8 files changed, 36 insertions(+), 66 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index d78d5fc173dc..78981928758e 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -471,17 +471,21 @@ EXPORT_SYMBOL_GPL(dma_buf_export);
*/
int dma_buf_fd(struct dma_buf *dmabuf, int flags)
{
+ struct file *file;
int fd;

- if (!dmabuf || !dmabuf->file)
+ if (!dmabuf)
return -EINVAL;

- fd = get_unused_fd_flags(flags);
- if (fd < 0)
- return fd;
-
- fd_install(fd, dmabuf->file);
+ file = dmabuf->file;
+ if (!file)
+ return -EINVAL;

+ fd = get_unused_fd_flags(flags);
+ if (fd >= 0)
+ fd_install(fd, file);
+ else
+ fput(file);
return fd;
}
EXPORT_SYMBOL_GPL(dma_buf_fd);
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 7856a9b3f8a8..06d1b7d3751a 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -662,8 +662,10 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
ret = drm_prime_add_buf_handle(&file_priv->prime,
dmabuf, handle);
mutex_unlock(&dev->object_name_lock);
- if (ret)
- goto fail_put_dmabuf;
+ if (unlikely(ret)) {
+ dma_buf_put(dmabuf);
+ goto out;
+ }

out_have_handle:
ret = dma_buf_fd(dmabuf, flags);
@@ -673,17 +675,10 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
* and that is invariant as long as a userspace gem handle exists.
* Closing the handle will clean out the cache anyway, so we don't leak.
*/
- if (ret < 0) {
- goto fail_put_dmabuf;
- } else {
+ if (ret >= 0) {
*prime_fd = ret;
ret = 0;
}
-
- goto out;
-
-fail_put_dmabuf:
- dma_buf_put(dmabuf);
out:
drm_gem_object_put_unlocked(obj);
out_unlock:
diff --git a/drivers/gpu/drm/i915/gvt/dmabuf.c b/drivers/gpu/drm/i915/gvt/dmabuf.c
index 6f4f8e941fc2..1783c724d96c 100644
--- a/drivers/gpu/drm/i915/gvt/dmabuf.c
+++ b/drivers/gpu/drm/i915/gvt/dmabuf.c
@@ -479,7 +479,7 @@ int intel_vgpu_get_dmabuf(struct intel_vgpu *vgpu, unsigned int dmabuf_id)
ret = dma_buf_fd(dmabuf, DRM_CLOEXEC | DRM_RDWR);
if (ret < 0) {
gvt_vgpu_err("create dma-buf fd failed ret:%d\n", ret);
- goto out_free_dmabuf;
+ goto out_free_gem;
}
dmabuf_fd = ret;

@@ -502,8 +502,6 @@ int intel_vgpu_get_dmabuf(struct intel_vgpu *vgpu, unsigned int dmabuf_id)

return dmabuf_fd;

-out_free_dmabuf:
- dma_buf_put(dmabuf);
out_free_gem:
i915_gem_object_put(obj);
out:
diff --git a/drivers/gpu/drm/ttm/ttm_object.c b/drivers/gpu/drm/ttm/ttm_object.c
index 1aa2baa83959..30d29d17653f 100644
--- a/drivers/gpu/drm/ttm/ttm_object.c
+++ b/drivers/gpu/drm/ttm/ttm_object.c
@@ -730,8 +730,7 @@ int ttm_prime_handle_to_fd(struct ttm_object_file *tfile,
if (ret >= 0) {
*prime_fd = ret;
ret = 0;
- } else
- dma_buf_put(dma_buf);
+ }

out_unref:
if (base)
diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index d3f7bb33a54d..3baf689241cc 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -1881,15 +1881,13 @@ int vb2_core_expbuf(struct vb2_queue *q, int *fd, unsigned int type,
if (ret < 0) {
dprintk(3, "buffer %d, plane %d failed to export (%d)\n",
index, plane, ret);
- dma_buf_put(dbuf);
- return ret;
+ } else {
+ dprintk(3, "buffer %d, plane %d exported as %d descriptor\n",
+ index, plane, ret);
+ *fd = ret;
+ ret = 0;
}
-
- dprintk(3, "buffer %d, plane %d exported as %d descriptor\n",
- index, plane, ret);
- *fd = ret;
-
- return 0;
+ return ret;
}
EXPORT_SYMBOL_GPL(vb2_core_expbuf);

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index e74db7902549..c9fcb2a2f518 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -381,7 +381,6 @@ int ion_alloc(size_t len, unsigned int heap_id_mask, unsigned int flags)
struct ion_buffer *buffer = NULL;
struct ion_heap *heap;
DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
- int fd;
struct dma_buf *dmabuf;

pr_debug("%s: len %zu heap_id_mask %u flags %x\n", __func__,
@@ -425,11 +424,7 @@ int ion_alloc(size_t len, unsigned int heap_id_mask, unsigned int flags)
return PTR_ERR(dmabuf);
}

- fd = dma_buf_fd(dmabuf, O_CLOEXEC);
- if (fd < 0)
- dma_buf_put(dmabuf);
-
- return fd;
+ return dma_buf_fd(dmabuf, O_CLOEXEC);
}

int ion_query_heaps(struct ion_heap_query *query)
diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
index dd46b758852a..1cb54f6f3c6a 100644
--- a/drivers/tee/tee_core.c
+++ b/drivers/tee/tee_core.c
@@ -125,7 +125,6 @@ static int tee_ioctl_version(struct tee_context *ctx,
static int tee_ioctl_shm_alloc(struct tee_context *ctx,
struct tee_ioctl_shm_alloc_data __user *udata)
{
- long ret;
struct tee_ioctl_shm_alloc_data data;
struct tee_shm *shm;

@@ -144,25 +143,18 @@ static int tee_ioctl_shm_alloc(struct tee_context *ctx,
data.flags = shm->flags;
data.size = shm->size;

- if (copy_to_user(udata, &data, sizeof(data)))
- ret = -EFAULT;
- else
- ret = tee_shm_get_fd(shm);
+ if (unlikely(copy_to_user(udata, &data, sizeof(data)))) {
+ tee_shm_put(shm);
+ return -EFAULT;
+ }

- /*
- * When user space closes the file descriptor the shared memory
- * should be freed or if tee_shm_get_fd() failed then it will
- * be freed immediately.
- */
- tee_shm_put(shm);
- return ret;
+ return tee_shm_get_fd(shm);
}

static int
tee_ioctl_shm_register(struct tee_context *ctx,
struct tee_ioctl_shm_register_data __user *udata)
{
- long ret;
struct tee_ioctl_shm_register_data data;
struct tee_shm *shm;

@@ -182,17 +174,12 @@ tee_ioctl_shm_register(struct tee_context *ctx,
data.flags = shm->flags;
data.length = shm->size;

- if (copy_to_user(udata, &data, sizeof(data)))
- ret = -EFAULT;
- else
- ret = tee_shm_get_fd(shm);
- /*
- * When user space closes the file descriptor the shared memory
- * should be freed or if tee_shm_get_fd() failed then it will
- * be freed immediately.
- */
- tee_shm_put(shm);
- return ret;
+ if (unlikely(copy_to_user(udata, &data, sizeof(data)))) {
+ tee_shm_put(shm);
+ return -EFAULT;
+ }
+
+ return tee_shm_get_fd(shm);
}

static int params_from_user(struct tee_context *ctx, struct tee_param *params,
diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index 07d3be6f0780..53b35b5e5776 100644
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -355,16 +355,10 @@ EXPORT_SYMBOL_GPL(tee_shm_register);
*/
int tee_shm_get_fd(struct tee_shm *shm)
{
- int fd;
-
if (!(shm->flags & TEE_SHM_DMA_BUF))
return -EINVAL;

- get_dma_buf(shm->dmabuf);
- fd = dma_buf_fd(shm->dmabuf, O_CLOEXEC);
- if (fd < 0)
- dma_buf_put(shm->dmabuf);
- return fd;
+ return dma_buf_fd(shm->dmabuf, O_CLOEXEC);
}

/**
--
2.17.0
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