[PATCH v4] efi: capsule-loader: Fix use-after-free in efi_capsule_write

[Hyunwoo Kim <imv4bel@gmail.com>]

A race condition may occur if the user calls close() on another
thread during a write() operation on the device node of the efi capsule.

This is a race condition that occurs between the efi_capsule_write()
and efi_capsule_flush() functions of efi_capsule_fops,
which ultimately results in UAF.

So, the page freeing process is modified to be done in
efi_capsule_release() instead of efi_capsule_flush().

Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
 drivers/firmware/efi/capsule-loader.c | 29 ++++++---------------------
 1 file changed, 6 insertions(+), 23 deletions(-)

diff --git a/drivers/firmware/efi/capsule-loader.c b/drivers/firmware/efi/capsule-loader.c
index 4dde8edd53b6..788e860304ae 100644
--- a/drivers/firmware/efi/capsule-loader.c
+++ b/drivers/firmware/efi/capsule-loader.c
@@ -243,18 +243,17 @@ static ssize_t efi_capsule_write(struct file *file, const char __user *buff,
 }
 
 /**
- * efi_capsule_flush - called by file close or file flush
+ * efi_capsule_release - called by file close
+ * @inode: not used
  * @file: file pointer
- * @id: not used
  *
- *	If a capsule is being partially uploaded then calling this function
- *	will be treated as upload termination and will free those completed
- *	buffer pages and -ECANCELED will be returned.
+ *	We will not free successfully submitted pages since efi update
+ *	requires data to be maintained across system reboot.
  **/
-static int efi_capsule_flush(struct file *file, fl_owner_t id)
+static int efi_capsule_release(struct inode *inode, struct file *file)
 {
-	int ret = 0;
 	struct capsule_info *cap_info = file->private_data;
+	int ret = 0;
 
 	if (cap_info->index > 0) {
 		pr_err("capsule upload not complete\n");
@@ -262,21 +261,6 @@ static int efi_capsule_flush(struct file *file, fl_owner_t id)
 		ret = -ECANCELED;
 	}
 
-	return ret;
-}
-
-/**
- * efi_capsule_release - called by file close
- * @inode: not used
- * @file: file pointer
- *
- *	We will not free successfully submitted pages since efi update
- *	requires data to be maintained across system reboot.
- **/
-static int efi_capsule_release(struct inode *inode, struct file *file)
-{
-	struct capsule_info *cap_info = file->private_data;
-
 	kfree(cap_info->pages);
 	kfree(cap_info->phys);
 	kfree(file->private_data);
@@ -324,7 +308,6 @@ static const struct file_operations efi_capsule_fops = {
 	.owner = THIS_MODULE,
 	.open = efi_capsule_open,
 	.write = efi_capsule_write,
-	.flush = efi_capsule_flush,
 	.release = efi_capsule_release,
 	.llseek = no_llseek,
 };
-- 
2.25.1