ima: Set file->f_mode instead of file->f_flags in ima_calc_file_hash()

Commit a408e4a8 ("ima: open a new file instance if no read
permissions") tries to create a new file descriptor to calculate a file
digest if the file has not been opened with O_RDONLY flag. However, if a
new file descriptor cannot be obtained, it sets the FMODE_READ flag to
file->f_flags instead of file->f_mode.

This patch fixes this issue by replacing f_flags with f_mode as it was
before that commit.

Cc: stable@vger.kernel.org # 4.20.x
Fixes: a408e4a8 ("ima: open a new file instance if no read permissions")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/ima/ima_crypto.c

@@ -411,7 +411,7 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
 	loff_t i_size;
 	int rc;
 	struct file *f = file;
-	bool new_file_instance = false, modified_flags = false;
+	bool new_file_instance = false, modified_mode = false;
 
 	/*
 	 * For consistency, fail file's opened with the O_DIRECT flag on
@@ -431,13 +431,13 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
 		f = dentry_open(&file->f_path, flags, file->f_cred);
 		if (IS_ERR(f)) {
 			/*
-			 * Cannot open the file again, lets modify f_flags
+			 * Cannot open the file again, lets modify f_mode
 			 * of original and continue
 			 */
 			pr_info_ratelimited("Unable to reopen file for reading.\n");
 			f = file;
-			f->f_flags |= FMODE_READ;
-			modified_flags = true;
+			f->f_mode |= FMODE_READ;
+			modified_mode = true;
 		} else {
 			new_file_instance = true;
 		}
@@ -455,8 +455,8 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
 out:
 	if (new_file_instance)
 		fput(f);
-	else if (modified_flags)
-		f->f_flags &= ~FMODE_READ;
+	else if (modified_mode)
+		f->f_mode &= ~FMODE_READ;
 	return rc;
 }