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Date: Tue, 11 Jul 2017 14:47:22 -0400
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
To: "J. Bruce Fields" <bfields@...ldses.org>,
Jeff Layton <jlayton@...nel.org>
Cc: "Serge E. Hallyn" <serge@...lyn.com>,
Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] integrity: track mtime in addition to i_version for
assessment
On Tue, 2017-07-11 at 12:13 -0400, J. Bruce Fields wrote:
> On Fri, Jul 07, 2017 at 10:05:30AM -0400, Jeff Layton wrote:
> > From: Jeff Layton <jlayton@...hat.com>
> >
> > The IMA assessment code tries to use the i_version counter to detect
> > when changes to a file have occurred. Many filesystems don't increment
> > it properly (or at all) so detecting changes with that is not always
> > reliable.
> >
> > That check should be gated on IS_I_VERSION, as you can't rely on the
> > i_version field changing unless that returns true.
> >
> > Have the code also track and check the mtime for the file. If the
> > IS_I_VERSION returns false, then use it to detect whether the file's
> > contents might have changed.
>
> Do they care about attribute changes? It's still better than nothing, I
> suppose.
IMA is only interested in file data changes, not file meta-data
changes. EVM needs to recalculate the hmac stored as security.evm,
when file meta-data changes (eg. xattrs, uid, gid, mode,
i_generations), but this is dependent on being in the setxattr or
notify_change() paths, not i_version.
Mimi
>
> I also wonder whether they should be mixing in ctime as I plan to for
> nfsd--the difference is whether they use it to check changes across
> reboots.
>
> --b.
>
> >
> > Signed-off-by: Jeff Layton <jlayton@...hat.com>
> > ---
> > security/integrity/ima/ima_api.c | 4 +++-
> > security/integrity/ima/ima_main.c | 32 ++++++++++++++++++++++++--------
> > security/integrity/integrity.h | 1 +
> > 3 files changed, 28 insertions(+), 9 deletions(-)
> >
> > v2: switch to storing/checking mtime instead of ctime
> >
> > diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
> > index c2edba8de35e..b8d746bbc43d 100644
> > --- a/security/integrity/ima/ima_api.c
> > +++ b/security/integrity/ima/ima_api.c
> > @@ -205,7 +205,8 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
> > } hash;
> >
> > if (!(iint->flags & IMA_COLLECTED)) {
> > - u64 i_version = file_inode(file)->i_version;
> > + u64 i_version = inode->i_version;
> > + struct timespec i_mtime = inode->i_mtime;
> >
> > if (file->f_flags & O_DIRECT) {
> > audit_cause = "failed(directio)";
> > @@ -225,6 +226,7 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
> > iint->ima_hash = tmpbuf;
> > memcpy(iint->ima_hash, &hash, length);
> > iint->version = i_version;
> > + iint->mtime = i_mtime;
> > iint->flags |= IMA_COLLECTED;
> > } else
> > result = -ENOMEM;
> > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> > index 2aebb7984437..8d12ef2d3ba2 100644
> > --- a/security/integrity/ima/ima_main.c
> > +++ b/security/integrity/ima/ima_main.c
> > @@ -113,6 +113,25 @@ static void ima_rdwr_violation_check(struct file *file,
> > "invalid_pcr", "open_writers");
> > }
> >
> > +static bool ima_should_update_iint(struct integrity_iint_cache *iint,
> > + struct inode *inode)
> > +{
> > + if (atomic_read(&inode->i_writecount) != 1)
> > + return false;
> > + if (iint->flags & IMA_NEW_FILE)
> > + return true;
> > + if (IS_I_VERSION(inode)) {
> > + if (iint->version != inode->i_version)
> > + return true;
> > + } else {
> > + if (iint->mtime.tv_sec != inode->i_mtime.tv_sec)
> > + return true;
> > + if (iint->mtime.tv_nsec != inode->i_mtime.tv_nsec)
> > + return true;
> > + }
> > + return false;
> > +}
> > +
> > static void ima_check_last_writer(struct integrity_iint_cache *iint,
> > struct inode *inode, struct file *file)
> > {
> > @@ -122,14 +141,11 @@ static void ima_check_last_writer(struct integrity_iint_cache *iint,
> > return;
> >
> > inode_lock(inode);
> > - if (atomic_read(&inode->i_writecount) == 1) {
> > - if ((iint->version != inode->i_version) ||
> > - (iint->flags & IMA_NEW_FILE)) {
> > - iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
> > - iint->measured_pcrs = 0;
> > - if (iint->flags & IMA_APPRAISE)
> > - ima_update_xattr(iint, file);
> > - }
> > + if (ima_should_update_iint(iint, inode)) {
> > + iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
> > + iint->measured_pcrs = 0;
> > + if (iint->flags & IMA_APPRAISE)
> > + ima_update_xattr(iint, file);
> > }
> > inode_unlock(inode);
> > }
> > diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
> > index a53e7e4ab06c..61fffa7583bf 100644
> > --- a/security/integrity/integrity.h
> > +++ b/security/integrity/integrity.h
> > @@ -102,6 +102,7 @@ struct integrity_iint_cache {
> > struct rb_node rb_node; /* rooted in integrity_iint_tree */
> > struct inode *inode; /* back pointer to inode in question */
> > u64 version; /* track inode changes */
> > + struct timespec mtime; /* track inode changes */
> > unsigned long flags;
> > unsigned long measured_pcrs;
> > enum integrity_status ima_file_status:4;
> > --
> > 2.13.0
> --
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