efi: capsule-loader: Fix use-after-free in efi_capsule_write

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 <[email protected]>

---
 drivers/firmware/efi/capsule-loader.c | 31 ++++++---------------------
 1 file changed, 7 insertions(+), 24 deletions(-)

drivers/firmware/efi/capsule-loader.c +7 -25

index 4dde8edd53b6..cec826adcb51 100644
@@ -242,29 +242,6 @@ static ssize_t efi_capsule_write(struct file *file, const char __user *buff,
        return ret;
 }
 
-/**
- * efi_capsule_flush - called by file close or file flush
- * @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.
- **/
-static int efi_capsule_flush(struct file *file, fl_owner_t id)
-{
-       int ret = 0;
-       struct capsule_info *cap_info = file->private_data;
-
-       if (cap_info->index > 0) {
-               pr_err("capsule upload not complete\n");
-               efi_free_all_buff_pages(cap_info);
-               ret = -ECANCELED;
-       }
-
-       return ret;
-}
-
 /**
  * efi_capsule_release - called by file close
  * @inode: not used

@@ -277,6 +254,13 @@ static int efi_capsule_release(struct inode *inode, struct file *file)
 {
        struct capsule_info *cap_info = file->private_data;
 
+       if (cap_info->index > 0 &&
+               (cap_info->header.headersize == 0 ||
+               cap_info->count < cap_info->total_size)) {
+               pr_err("capsule upload not complete\n");
+               efi_free_all_buff_pages(cap_info);
+       }
+
        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

Thanks for the fix, I will queue it up before the end of the week.