ANDROID: Add filp_open_block() for zram

We currently plan to disallow use of filp_open() from drivers in GKI, however the ZRAM driver still needs it. Add a new GKI-only variant of filp_open() which only permits a block device to be opened, which can be exported instead. This keeps ZRAM working but cuts down on drivers that attempt to open and write files in kernel mode. Bug: 179220339 Bug: 205141088 Change-Id: Id696b4aaf204b0499ce0a1b6416648670236e570 Signed-off-by: Alistair Delva <[email protected]> (cherry picked from commit 62d9cb66f6bf79c6dbe7c556184ccd8cc791d719)
OnePlusOSS · Apr 21, 2023 · d7595b4 · d7595b4
1 parent 3183446
commit d7595b4
Show file tree

Hide file tree

Showing 3 changed files with 23 additions and 1 deletion.
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
@@ -505,7 +505,7 @@ static ssize_t backing_dev_store(struct device *dev,
 	if (sz > 0 && file_name[sz - 1] == '\n')
 		file_name[sz - 1] = 0x00;
 
-	backing_dev = filp_open(file_name, O_RDWR|O_LARGEFILE, 0);
+	backing_dev = filp_open_block(file_name, O_RDWR|O_LARGEFILE, 0);
 	if (IS_ERR(backing_dev)) {
 		err = PTR_ERR(backing_dev);
 		backing_dev = NULL;

diff --git a/fs/open.c b/fs/open.c
@@ -1281,6 +1281,27 @@ struct file *filp_open(const char *filename, int flags, umode_t mode)
 }
 EXPORT_SYMBOL(filp_open);
 
+
+/* ANDROID: Allow drivers to open only block files from kernel mode */
+struct file *filp_open_block(const char *filename, int flags, umode_t mode)
+{
+	struct file *file;
+
+	file = filp_open(filename, flags, mode);
+	if (IS_ERR(file))
+		goto err_out;
+
+	/* Drivers should only be allowed to open block devices */
+	if (!S_ISBLK(file->f_mapping->host->i_mode)) {
+		filp_close(file, NULL);
+		file = ERR_PTR(-ENOTBLK);
+	}
+
+err_out:
+	return file;
+}
+EXPORT_SYMBOL_GPL(filp_open_block);
+
 struct file *file_open_root(const struct path *root,
 			    const char *filename, int flags, umode_t mode)
 {

diff --git a/include/linux/fs.h b/include/linux/fs.h
@@ -2771,6 +2771,7 @@ extern long do_sys_open(int dfd, const char __user *filename, int flags,
 			umode_t mode);
 extern struct file *file_open_name(struct filename *, int, umode_t);
 extern struct file *filp_open(const char *, int, umode_t);
+extern struct file *filp_open_block(const char *, int, umode_t);
 extern struct file *file_open_root(const struct path *,
 				   const char *, int, umode_t);
 static inline struct file *file_open_root_mnt(struct vfsmount *mnt,