efi: Handle deletions and size changes in efivarfs_write_file

A write to an efivarfs file will not always result in a variable of
'count' size after the EFI SetVariable() call. We may have appended to
the existing data (ie, with the EFI_VARIABLE_APPEND_WRITE attribute), or
even have deleted the variable (with an authenticated variable update,
with a zero datasize).

This change re-reads the updated variable from firmware, to check for
size changes and deletions. In the latter case, we need to drop the
dentry.

Signed-off-by: Jeremy Kerr <jeremy.kerr@canonical.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

1 files changed, 39 insertions, 10 deletions

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index b605c4849772..d7658b4a5010 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -658,6 +658,7 @@ static ssize_t efivarfs_file_write(struct file *file,
         u32 attributes;
         struct inode *inode = file->f_mapping->host;
         int datasize = count - sizeof(attributes);
+        unsigned long newdatasize;
 
         if (count < sizeof(attributes))
                 return -EINVAL;
@@ -696,32 +697,60 @@ static ssize_t efivarfs_file_write(struct file *file,
 
         switch (status) {
         case EFI_SUCCESS:
-                mutex_lock(&inode->i_mutex);
-                i_size_write(inode, count);
-                mutex_unlock(&inode->i_mutex);
                 break;
         case EFI_INVALID_PARAMETER:
                 count = -EINVAL;
-                break;
+                goto out;
         case EFI_OUT_OF_RESOURCES:
                 count = -ENOSPC;
-                break;
+                goto out;
         case EFI_DEVICE_ERROR:
                 count = -EIO;
-                break;
+                goto out;
         case EFI_WRITE_PROTECTED:
                 count = -EROFS;
-                break;
+                goto out;
         case EFI_SECURITY_VIOLATION:
                 count = -EACCES;
-                break;
+                goto out;
         case EFI_NOT_FOUND:
                 count = -ENOENT;
-                break;
+                goto out;
         default:
                 count = -EINVAL;
-                break;
+                goto out;
         }
+
+        /*
+         * Writing to the variable may have caused a change in size (which
+         * could either be an append or an overwrite), or the variable to be
+         * deleted. Perform a GetVariable() so we can tell what actually
+         * happened.
+         */
+        newdatasize = 0;
+        status = efivars->ops->get_variable(var->var.VariableName,
+                                            &var->var.VendorGuid,
+                                            NULL, &newdatasize,
+                                            NULL);
+
+        if (status == EFI_BUFFER_TOO_SMALL) {
+                mutex_lock(&inode->i_mutex);
+                i_size_write(inode, newdatasize + sizeof(attributes));
+                mutex_unlock(&inode->i_mutex);
+
+        } else if (status == EFI_NOT_FOUND) {
+                spin_lock(&efivars->lock);
+                list_del(&var->list);
+                spin_unlock(&efivars->lock);
+                efivar_unregister(var);
+                drop_nlink(inode);
+                dput(file->f_dentry);
+
+        } else {
+                pr_warn("efivarfs: inconsistent EFI variable implementation? "
+                                "status = %lx\n", status);
+        }
+
 out:
         kfree(data);