[PATCH v5 12/16] IMA: Add support for file reads without contents

From: Kees Cook <keescook@chromium.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kees Cook <keescook@chromium.org>,
	Scott Branden <scott.branden@broadcom.com>,
	Mimi Zohar <zohar@linux.ibm.com>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Takashi Iwai <tiwai@suse.de>, Jessica Yu <jeyu@kernel.org>,
	SeongJae Park <sjpark@amazon.de>, KP Singh <kpsingh@chromium.org>,
	linux-efi@vger.kernel.org, linux-security-module@vger.kernel.org,
	linux-integrity@vger.kernel.org, selinux@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v5 12/16] IMA: Add support for file reads without contents
Date: Fri,  2 Oct 2020 10:38:24 -0700	[thread overview]
Message-ID: <20201002173828.2099543-13-keescook@chromium.org> (raw)
In-Reply-To: <20201002173828.2099543-1-keescook@chromium.org>

From: Scott Branden <scott.branden@broadcom.com>

When the kernel_read_file LSM hook is called with contents=false, IMA
can appraise the file directly, without requiring a filled buffer. When
such a buffer is available, though, IMA can continue to use it instead
of forcing a double read here.

Signed-off-by: Scott Branden <scott.branden@broadcom.com>
Link: https://lore.kernel.org/lkml/20200706232309.12010-10-scott.branden@broadcom.com/
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/ima/ima_main.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 939f53d02627..82c9d62bcb11 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -613,11 +613,8 @@ void ima_post_path_mknod(struct dentry *dentry)
 int ima_read_file(struct file *file, enum kernel_read_file_id read_id,
 		  bool contents)
 {
-	/* Reject all partial reads during appraisal. */
-	if (!contents) {
-		if (ima_appraise & IMA_APPRAISE_ENFORCE)
-			return -EACCES;
-	}
+	enum ima_hooks func;
+	u32 secid;
 
 	/*
 	 * Do devices using pre-allocated memory run the risk of the
@@ -626,7 +623,20 @@ int ima_read_file(struct file *file, enum kernel_read_file_id read_id,
 	 * buffers? It may be desirable to include the buffer address
 	 * in this API and walk all the dma_map_single() mappings to check.
 	 */
-	return 0;
+
+	/*
+	 * There will be a call made to ima_post_read_file() with
+	 * a filled buffer, so we don't need to perform an extra
+	 * read early here.
+	 */
+	if (contents)
+		return 0;
+
+	/* Read entire file for all partial reads. */
+	func = read_idmap[read_id] ?: FILE_CHECK;
+	security_task_getsecid(current, &secid);
+	return process_measurement(file, current_cred(), secid, NULL,
+				   0, MAY_READ, func);
 }
 
 const int read_idmap[READING_MAX_ID] = {
-- 
2.25.1

