Commit b836c4d2 authored by Mimi Zohar's avatar Mimi Zohar
Browse files

ima: detect changes to the backing overlay file 



Commit 18b44bc5 ("ovl: Always reevaluate the file signature for
IMA") forced signature re-evaulation on every file access.

Instead of always re-evaluating the file's integrity, detect a change
to the backing file, by comparing the cached file metadata with the
backing file's metadata.  Verifying just the i_version has not changed
is insufficient.  In addition save and compare the i_ino and s_dev
as well.

Reviewed-by: default avatarAmir Goldstein <amir73il@gmail.com>
Tested-by: default avatarEric Snowberg <eric.snowberg@oracle.com>
Tested-by: default avatarRaul E Rangel <rrangel@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarMimi Zohar <zohar@linux.ibm.com>
parent b4650306

fs/overlayfs/super.c

+1 −1
Original line number Diff line number Diff line
@@ -1489,7 +1489,7 @@ int ovl_fill_super(struct super_block *sb, struct fs_context *fc) 
		ovl_trusted_xattr_handlers;

	sb->s_fs_info = ofs;

	sb->s_flags |= SB_POSIXACL;

	sb->s_iflags |= SB_I_SKIP_SYNC | SB_I_IMA_UNVERIFIABLE_SIGNATURE;

	sb->s_iflags |= SB_I_SKIP_SYNC;



	err = -ENOMEM;

	root_dentry = ovl_get_root(sb, ctx->upper.dentry, oe);

security/integrity/ima/ima_api.c

+5 −0
Original line number Diff line number Diff line
@@ -243,6 +243,7 @@ int ima_collect_measurement(struct integrity_iint_cache *iint, 
{

	const char *audit_cause = "failed";

	struct inode *inode = file_inode(file);

	struct inode *real_inode = d_real_inode(file_dentry(file));

	const char *filename = file->f_path.dentry->d_name.name;

	struct ima_max_digest_data hash;

	struct kstat stat;
@@ -302,6 +303,10 @@ int ima_collect_measurement(struct integrity_iint_cache *iint, 
	iint->ima_hash = tmpbuf;

	memcpy(iint->ima_hash, &hash, length);

	iint->version = i_version;

	if (real_inode != inode) {

		iint->real_ino = real_inode->i_ino;

		iint->real_dev = real_inode->i_sb->s_dev;

	}



	/* Possibly temporary failure due to type of read (eg. O_DIRECT) */

	if (!result)

security/integrity/ima/ima_main.c

+15 −1
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ 
#include <linux/xattr.h>

#include <linux/ima.h>

#include <linux/fs.h>

#include <linux/iversion.h>



#include "ima.h"
@@ -207,7 +208,7 @@ static int process_measurement(struct file *file, const struct cred *cred, 
			       u32 secid, char *buf, loff_t size, int mask,

			       enum ima_hooks func)

{

	struct inode *inode = file_inode(file);

	struct inode *backing_inode, *inode = file_inode(file);

	struct integrity_iint_cache *iint = NULL;

	struct ima_template_desc *template_desc = NULL;

	char *pathbuf = NULL;
@@ -284,6 +285,19 @@ static int process_measurement(struct file *file, const struct cred *cred, 
		iint->measured_pcrs = 0;

	}



	/* Detect and re-evaluate changes made to the backing file. */

	backing_inode = d_real_inode(file_dentry(file));

	if (backing_inode != inode &&

	    (action & IMA_DO_MASK) && (iint->flags & IMA_DONE_MASK)) {

		if (!IS_I_VERSION(backing_inode) ||

		    backing_inode->i_sb->s_dev != iint->real_dev ||

		    backing_inode->i_ino != iint->real_ino ||

		    !inode_eq_iversion(backing_inode, iint->version)) {

			iint->flags &= ~IMA_DONE_MASK;

			iint->measured_pcrs = 0;

		}

	}



	/* Determine if already appraised/measured based on bitmask

	 * (IMA_MEASURE, IMA_MEASURED, IMA_XXXX_APPRAISE, IMA_XXXX_APPRAISED,

	 *  IMA_AUDIT, IMA_AUDITED)

security/integrity/integrity.h

+2 −0
Original line number Diff line number Diff line
@@ -164,6 +164,8 @@ struct integrity_iint_cache { 
	unsigned long flags;

	unsigned long measured_pcrs;

	unsigned long atomic_flags;

	unsigned long real_ino;

	dev_t real_dev;

	enum integrity_status ima_file_status:4;

	enum integrity_status ima_mmap_status:4;

	enum integrity_status ima_bprm_status:4;