Commit 18b44bc5a672 ("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.
Signed-off-by: Mimi Zohar <[email protected]>
---
Changelog:
- Changes made based on Amir's review:
v2: Use s_dev, not i_rdev. Limit setting real_ino, real_dev.
v1: Removal of unnecessary overlay magic test. Verify i_version, i_ino
and i_rdev haven't changed.
fs/overlayfs/super.c | 2 +-
security/integrity/ima/ima_api.c | 5 +++++
security/integrity/ima/ima_main.c | 16 +++++++++++++++-
security/integrity/integrity.h | 2 ++
4 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 3fa2416264a4..c71d185980c0 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -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);
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 452e80b541e5..597ea0c4d72f 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -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)
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 365db0e43d7c..cc1217ac2c6f 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -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)
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index d7553c93f5c0..9561db7cf6b4 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -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;
--
2.39.3
On Wed, Oct 25, 2023 at 8:39 AM Mimi Zohar <[email protected]> wrote:
> + 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;
> + }
> + }
> +
Does this mean I need to mount ext4 with `-o iversion`? Or has it been
enabled by default?
I can test this patch out sometime this week and verify it fixes the
performance regression.
Thanks!
On Wed, 2023-10-25 at 08:59 -0600, Raul Rangel wrote:
> On Wed, Oct 25, 2023 at 8:39 AM Mimi Zohar <[email protected]> wrote:
> > + 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;
> > + }
> > + }
> > +
> Does this mean I need to mount ext4 with `-o iversion`? Or has it been
> enabled by default?
According to commit 1ff20307393e ("ext4: unconditionally enable the
i_version counter") it's now enabled by default.
>
> I can test this patch out sometime this week and verify it fixes the
> performance regression.
>
> Thanks!
Much appreciated!
--
thanks,
Mimi
> On Oct 25, 2023, at 8:39 AM, Mimi Zohar <[email protected]> wrote:
>
> Commit 18b44bc5a672 ("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.
>
> Signed-off-by: Mimi Zohar <[email protected]>
I ran the file integrity tests that originally uncovered the need for
"Commit 18b44bc5a672 ("ovl: Always reevaluate the file signature for
IMA”). When the backing file is changed, file integrity remains. For that
part, feel free to add:
Tested-by: Eric Snowberg <[email protected]>
On Wed, 2023-10-25 at 16:27 +0000, Eric Snowberg wrote:
>
> > On Oct 25, 2023, at 8:39 AM, Mimi Zohar <[email protected]> wrote:
> >
> > Commit 18b44bc5a672 ("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.
> >
> > Signed-off-by: Mimi Zohar <[email protected]>
>
> I ran the file integrity tests that originally uncovered the need for
> "Commit 18b44bc5a672 ("ovl: Always reevaluate the file signature for
> IMA”). When the backing file is changed, file integrity remains. For that
> part, feel free to add:
>
> Tested-by: Eric Snowberg <[email protected]>
Thanks!
Mimi
On Wed, Oct 25, 2023 at 12:01 PM Mimi Zohar <[email protected]> wrote:
>
> On Wed, 2023-10-25 at 16:27 +0000, Eric Snowberg wrote:
> >
> > > On Oct 25, 2023, at 8:39 AM, Mimi Zohar <[email protected]> wrote:
> > >
> > > Commit 18b44bc5a672 ("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.
> > >
> > > Signed-off-by: Mimi Zohar <[email protected]>
> >
> > I ran the file integrity tests that originally uncovered the need for
> > "Commit 18b44bc5a672 ("ovl: Always reevaluate the file signature for
> > IMA”). When the backing file is changed, file integrity remains. For that
> > part, feel free to add:
> >
> > Tested-by: Eric Snowberg <[email protected]>
>
> Thanks!
>
> Mimi
>
I just verified this fixes the speed regression:
```
rrangel920 / # time clang --version >/dev/null
real 0m0.369s
user 0m0.000s
sys 0m0.368s
rrangel920 / #
rrangel920 / # time clang --version >/dev/null
real 0m0.017s
user 0m0.004s
sys 0m0.013s
rrangel920 / # time clang --version >/dev/null
real 0m0.012s
user 0m0.000s
sys 0m0.012s
rrangel920 / # time clang --version >/dev/null
real 0m0.012s
user 0m0.000s
sys 0m0.012s
```
Tested-by: Raul E Rangel <[email protected]>
Thanks again for the quick fix!