dma-buf: propagate errors from dma_buf_describe() on debugfs read

The callback function dma_buf_describe() returns an int not void so the
function pointer cast in dma_buf_show() is wrong. dma_buf_describe() can
also fail when acquiring the mutex gets interrupted so always returning
0 in dma_buf_show() is wrong, too.

Fix both issues by avoiding the indirection via dma_buf_show() and call
dma_buf_describe() directly. Rename it to dma_buf_debug_show() to get it
in line with the other functions.

This type mismatch was caught by the PaX RAP plugin.
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Brad Spengler <spender@grsecurity.net>
Cc: PaX Team <pageexec@freemail.hu>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>

drivers/dma-buf/dma-buf.c

@@ -824,7 +824,7 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
 EXPORT_SYMBOL_GPL(dma_buf_vunmap);
 
 #ifdef CONFIG_DEBUG_FS
-static int dma_buf_describe(struct seq_file *s)
+static int dma_buf_debug_show(struct seq_file *s, void *unused)
 {
 	int ret;
 	struct dma_buf *buf_obj;
@@ -879,17 +879,9 @@ static int dma_buf_describe(struct seq_file *s)
 	return 0;
 }
 
-static int dma_buf_show(struct seq_file *s, void *unused)
-{
-	void (*func)(struct seq_file *) = s->private;
-
-	func(s);
-	return 0;
-}
-
 static int dma_buf_debug_open(struct inode *inode, struct file *file)
 {
-	return single_open(file, dma_buf_show, inode->i_private);
+	return single_open(file, dma_buf_debug_show, NULL);
 }
 
 static const struct file_operations dma_buf_debug_fops = {
@@ -913,7 +905,7 @@ static int dma_buf_init_debugfs(void)
 		return err;
 	}
 
-	err = dma_buf_debugfs_create_file("bufinfo", dma_buf_describe);
+	err = dma_buf_debugfs_create_file("bufinfo", NULL);
 
 	if (err)
 		pr_debug("dma_buf: debugfs: failed to create node bufinfo\n");