Messages in this thread | | | Date | Mon, 17 Apr 2023 10:07:05 -0400 | Subject | Re: [PATCH] overlayfs: Trigger file re-evaluation by IMA / EVM after writes | From | Stefan Berger <> |
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On 4/6/23 18:04, Jeff Layton wrote: > On Thu, 2023-04-06 at 17:24 -0400, Jeff Layton wrote: >> On Thu, 2023-04-06 at 16:22 -0400, Stefan Berger wrote: >>> >>> On 4/6/23 15:37, Jeff Layton wrote: >>>> On Thu, 2023-04-06 at 15:11 -0400, Stefan Berger wrote: >>>>> >>>>> On 4/6/23 14:46, Jeff Layton wrote: >>>>>> On Thu, 2023-04-06 at 17:01 +0200, Christian Brauner wrote: >>>>>>> On Thu, Apr 06, 2023 at 10:36:41AM -0400, Paul Moore wrote: >>>>> >>>>>> >>>>>> Correct. As long as IMA is also measuring the upper inode then it seems >>>>>> like you shouldn't need to do anything special here. >>>>> >>>>> Unfortunately IMA does not notice the changes. With the patch provided in the other email IMA works as expected. >>>>> >>>> >>>> >>>> It looks like remeasurement is usually done in ima_check_last_writer. >>>> That gets called from __fput which is called when we're releasing the >>>> last reference to the struct file. >>>> >>>> You've hooked into the ->release op, which gets called whenever >>>> filp_close is called, which happens when we're disassociating the file >>>> from the file descriptor table. >>>> >>>> So...I don't get it. Is ima_file_free not getting called on your file >>>> for some reason when you go to close it? It seems like that should be >>>> handling this. >>> >>> I would ditch the original proposal in favor of this 2-line patch shown here: >>> >>> https://lore.kernel.org/linux-integrity/a95f62ed-8b8a-38e5-e468-ecbde3b221af@linux.ibm.com/T/#m3bd047c6e5c8200df1d273c0ad551c645dd43232 >>> >>> >> >> Ok, I think I get it. IMA is trying to use the i_version from the >> overlayfs inode. >> >> I suspect that the real problem here is that IMA is just doing a bare >> inode_query_iversion. Really, we ought to make IMA call >> vfs_getattr_nosec (or something like it) to query the getattr routine in >> the upper layer. Then overlayfs could just propagate the results from >> the upper layer in its response. >> >> That sort of design may also eventually help IMA work properly with more >> exotic filesystems, like NFS or Ceph. >> >> >> > > Maybe something like this? It builds for me but I haven't tested it. It > looks like overlayfs already should report the upper layer's i_version > in getattr, though I haven't tested that either: > > -----------------------8<--------------------------- > > [PATCH] IMA: use vfs_getattr_nosec to get the i_version > > IMA currently accesses the i_version out of the inode directly when it > does a measurement. This is fine for most simple filesystems, but can be > problematic with more complex setups (e.g. overlayfs). > > Make IMA instead call vfs_getattr_nosec to get this info. This allows > the filesystem to determine whether and how to report the i_version, and > should allow IMA to work properly with a broader class of filesystems in > the future. > > Reported-by: Stefan Berger <stefanb@linux.ibm.com> > Signed-off-by: Jeff Layton <jlayton@kernel.org> > --- > security/integrity/ima/ima_api.c | 9 ++++++--- > security/integrity/ima/ima_main.c | 12 ++++++++---- > 2 files changed, 14 insertions(+), 7 deletions(-) > > diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c > index d3662f4acadc..c45902e72044 100644 > --- a/security/integrity/ima/ima_api.c > +++ b/security/integrity/ima/ima_api.c > @@ -13,7 +13,6 @@ > #include <linux/fs.h> > #include <linux/xattr.h> > #include <linux/evm.h> > -#include <linux/iversion.h> > #include <linux/fsverity.h> > > #include "ima.h" > @@ -246,10 +245,11 @@ int ima_collect_measurement(struct integrity_iint_cache *iint, > struct inode *inode = file_inode(file); > const char *filename = file->f_path.dentry->d_name.name; > struct ima_max_digest_data hash; > + struct kstat stat; > int result = 0; > int length; > void *tmpbuf; > - u64 i_version; > + u64 i_version = 0; > > /* > * Always collect the modsig, because IMA might have already collected > @@ -268,7 +268,10 @@ int ima_collect_measurement(struct integrity_iint_cache *iint, > * to an initial measurement/appraisal/audit, but was modified to > * assume the file changed. > */ > - i_version = inode_query_iversion(inode); > + result = vfs_getattr_nosec(&file->f_path, &stat, STATX_CHANGE_COOKIE, > + AT_STATX_SYNC_AS_STAT); > + if (!result && (stat.result_mask & STATX_CHANGE_COOKIE)) > + i_version = stat.change_cookie; > hash.hdr.algo = algo; > hash.hdr.length = hash_digest_size[algo]; > > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c > index d66a0a36415e..365db0e43d7c 100644 > --- a/security/integrity/ima/ima_main.c > +++ b/security/integrity/ima/ima_main.c > @@ -24,7 +24,6 @@ > #include <linux/slab.h> > #include <linux/xattr.h> > #include <linux/ima.h> > -#include <linux/iversion.h> > #include <linux/fs.h> > > #include "ima.h" > @@ -164,11 +163,16 @@ static void ima_check_last_writer(struct integrity_iint_cache *iint, > > mutex_lock(&iint->mutex); > if (atomic_read(&inode->i_writecount) == 1) { > + struct kstat stat; > + > update = test_and_clear_bit(IMA_UPDATE_XATTR, > &iint->atomic_flags); > - if (!IS_I_VERSION(inode) || > - !inode_eq_iversion(inode, iint->version) || > - (iint->flags & IMA_NEW_FILE)) { > + if ((iint->flags & IMA_NEW_FILE) || > + vfs_getattr_nosec(&file->f_path, &stat, > + STATX_CHANGE_COOKIE, > + AT_STATX_SYNC_AS_STAT) || > + !(stat.result_mask & STATX_CHANGE_COOKIE) || > + stat.change_cookie != iint->version) { > iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE); > iint->measured_pcrs = 0; > if (update)
I tested this in the OpenBMC setup with overlayfs acting as rootfs. It works now as expected.
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
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