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ima: detect changes to the backing overlay file

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commit b836c4d29f upstream.

Commit 18b44bc5a6 ("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: Amir Goldstein <amir73il@gmail.com>
Tested-by: Eric Snowberg <eric.snowberg@oracle.com>
Tested-by: Raul E Rangel <rrangel@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mimi Zohar 2023-10-18 14:47:02 -04:00 committed by Greg Kroah-Hartman
parent f2f0144e82
commit 0d29174959
4 changed files with 23 additions and 2 deletions
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2
fs/overlayfs/super.c
View File

@ -1467,7 +1467,7 @@ 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);

5
security/integrity/ima/ima_api.c
View File

@ -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)

16
security/integrity/ima/ima_main.c
View File

@ -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)

2
security/integrity/integrity.h
View File

@ -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;