From: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
Add a refcount for kernel to prevent UAF(Use After Free) issue.
We can assume a case like below:
1. kernel space alloc dma_buf(file count = 1)
2. kernel use dma_buf to get fd(file count = 1)
3. userspace use fd to do mapping (file count = 2)
4. kernel call dma_buf_put (file count = 1)
5. userpsace close buffer fd(file count = 0)
6. at this time, buffer is released, but va is valid!!
So we still can read/write buffer via mmap va,
it maybe cause memory leak, or kernel exception.
And also, if we use "ls -ll" to watch corresponding process
fd link info, it also will cause kernel exception.
Another case:
Using dma_buf_fd to generate more than 1 fd, because
dma_buf_fd will not increase file count, thus, when close
the second fd, it maybe occurs error.
Solution:
Add a kernel count for dma_buf, and make sure the file count
of dma_buf.file hold by kernel is 1.
Notes: For this solution, kref couldn't work because kernel ref
maybe added from 0, but kref don't allow it.
Signed-off-by: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
---
drivers/dma-buf/dma-buf.c | 23 +++++++++++++++++++----
include/linux/dma-buf.h | 6 ++++--
2 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 511fe0d217a0..04ee92aac8b9 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -62,6 +62,7 @@ static void dma_buf_release(struct dentry *dentry)
if (unlikely(!dmabuf))
return;
+ WARN_ON(atomic64_read(&dmabuf->kernel_ref));
BUG_ON(dmabuf->vmapping_counter);
/*
@@ -555,6 +556,7 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
goto err_module;
}
+ atomic64_set(&dmabuf->kernel_ref, 1);
dmabuf->priv = exp_info->priv;
dmabuf->ops = exp_info->ops;
dmabuf->size = exp_info->size;
@@ -617,6 +619,9 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags)
fd_install(fd, dmabuf->file);
+ /* Add file cnt for each new fd */
+ get_file(dmabuf->file);
+
return fd;
}
EXPORT_SYMBOL_GPL(dma_buf_fd);
@@ -626,12 +631,13 @@ EXPORT_SYMBOL_GPL(dma_buf_fd);
* @fd: [in] fd associated with the struct dma_buf to be returned
*
* On success, returns the struct dma_buf associated with an fd; uses
- * file's refcounting done by fget to increase refcount. returns ERR_PTR
- * otherwise.
+ * dmabuf's ref refcounting done by kref_get to increase refcount.
+ * Returns ERR_PTR otherwise.
*/
struct dma_buf *dma_buf_get(int fd)
{
struct file *file;
+ struct dma_buf *dmabuf;
file = fget(fd);
@@ -643,7 +649,12 @@ struct dma_buf *dma_buf_get(int fd)
return ERR_PTR(-EINVAL);
}
- return file->private_data;
+ dmabuf = file->private_data;
+ /* replace file count increase as ref increase for kernel user */
+ get_dma_buf(dmabuf);
+ fput(file);
+
+ return dmabuf;
}
EXPORT_SYMBOL_GPL(dma_buf_get);
@@ -662,7 +673,11 @@ void dma_buf_put(struct dma_buf *dmabuf)
if (WARN_ON(!dmabuf || !dmabuf->file))
return;
- fput(dmabuf->file);
+ if (WARN_ON(!atomic64_read(&dmabuf->kernel_ref)))
+ return;
+
+ if (!atomic64_dec_return(&dmabuf->kernel_ref))
+ fput(dmabuf->file);
}
EXPORT_SYMBOL_GPL(dma_buf_put);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index efdc56b9d95f..bc790cb028eb 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -308,6 +308,7 @@ struct dma_buf_ops {
struct dma_buf {
size_t size;
struct file *file;
+ atomic64_t kernel_ref;
struct list_head attachments;
const struct dma_buf_ops *ops;
struct mutex lock;
@@ -436,7 +437,7 @@ struct dma_buf_export_info {
.owner = THIS_MODULE }
/**
- * get_dma_buf - convenience wrapper for get_file.
+ * get_dma_buf - increase a kernel ref of dma-buf
* @dmabuf: [in] pointer to dma_buf
*
* Increments the reference count on the dma-buf, needed in case of drivers
@@ -446,7 +447,8 @@ struct dma_buf_export_info {
*/
static inline void get_dma_buf(struct dma_buf *dmabuf)
{
- get_file(dmabuf->file);
+ if (atomic64_inc_return(&dmabuf->kernel_ref) == 1)
+ get_file(dmabuf->file);
}
/**
--
2.17.1
