From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1FDC631B82C; Thu, 15 Jan 2026 19:45:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768506325; cv=none; b=mbjgjX0wtlZg64QHtsI6DUOw7SGvFX5luaQFbuup6qReXU1I+0oL495xUi4U0F7pQbpNAm2xletIHIMYCQwTSqucEL1gOozIRuY5D2/3R4/uCVdnnqbbO3naYQYBft01JUEqowGwxNLMERNxTUTL4bKE31lQG+Bi7xeUYq4RGSs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768506325; c=relaxed/simple; bh=x3FYtI8iDJviH7evvP2YDiOUNR32l1yIB1H5jGtGrFs=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=ckOchmGFq0Z3x2beQuWp5vjlwbXFpt3Dn9fnmUVTqikMSlnk0jPNdtKho8YdNPaU0xLyeIZnSyW5V5VX91tvHr4H5nDL4hPfkOpsGgGhpgFUwXlqNtkPnoezBMyvyPoFDz9wcbPlIC+db5P21Z7j3g8QNnzvn+xELSX+mNiiAA4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KxlQh0Wd; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="KxlQh0Wd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 26B8EC116D0; Thu, 15 Jan 2026 19:45:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768506324; bh=x3FYtI8iDJviH7evvP2YDiOUNR32l1yIB1H5jGtGrFs=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=KxlQh0WdJadW09V9+zLDyK8A54SKJ48BQWE30hPcFi7qpWJQvA7DC0WpF2xTJ563n NYh3Bvo/baE5Sk9bsRqcQ3oFB3kWXDT2vFTigJkwi1RdJNFMTmrA1DsTmzWvRTytIh FY59lGpf06RQouYtesT4k2BnXYUAZbX5Uu6GQQkT9rykx32ikpVQMMLSTPb2haUY8C ZlUmx/T2SVib2jZoiIdbpM1bGHzoeu2GC2HkjkcbOadpsEnCESvsm3dcMI4LFxSp4t gKNw0RxgsxRctYEQ2a6z62bSue2ksSAVOMGGPW4uzkaLnnUROm3xsmGzp2eeLBsjRR NVQllky9MC2gw== Message-ID: <1f4b4ff2ba92560f8b3cdd441e0844758eb080a4.camel@kernel.org> Subject: Re: [PATCH] ima: Detect changes to files via kstat changes rather than i_version From: Jeff Layton To: Frederick Lawler , Roberto Sassu Cc: Mimi Zohar , Roberto Sassu , Dmitry Kasatkin , Eric Snowberg , Paul Moore , James Morris , "Serge E. Hallyn" , "Darrick J. Wong" , Christian Brauner , Josef Bacik , linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, kernel-team@cloudflare.com Date: Thu, 15 Jan 2026 14:45:22 -0500 In-Reply-To: References: <20260112-xfs-ima-fixup-v1-1-8d13b6001312@cloudflare.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ cDEsvv5IMmeMe1/qLZ6NaVkNuL3WOXvxaVT9USW1+/SGipO2IpKJjeDZfehlB/kpfF24+RrK+seQf 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Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2026-01-15 at 12:10 -0600, Frederick Lawler wrote: > On Thu, Jan 15, 2026 at 12:46:37PM +0100, Roberto Sassu wrote: > > On Mon, 2026-01-12 at 16:32 -0600, Frederick Lawler wrote: > > > Commit 1cf7e834a6fb ("xfs: switch to multigrain timestamps") > > > introduced a means to track change detection for an inode > > > via ctime updates, opposed to setting kstat.change_cookie when > > > calling into xfs_vn_getattr(). > > >=20 > > > This introduced a regression because IMA caches kstat.change_cookie > > > to compare against an inode's i_version directly in > > > integrity_inode_attrs_changed(), and thus could be out of date > > > depending on how file systems increment i_version. > > >=20 > > > To address this, require integrity_inode_attrs_changed() to query > > > vfs_getattr_nosec() to compare the cached version against > > > kstat.change_cookie directly. This ensures that when updates occur, > > > we're accessing the same changed inode version on changes, and fallba= ck > > > to compare against an artificial version generated from kstat.ctime > > > via integrity_ctime_guard() when there's no detected change > > > to the kstat.change_cookie. > > >=20 > > > This ensures that in the absence of i_version support for file system= s, > > > and in the absence of a kstat.change_cookie update, we ultimately hav= e a > > > unique-enough version to compare against. > > >=20 > > > The exact implementation for integrity_ctime_guard() is to ensure tha= t > > > if tv_sec or tv_nsec are zero, there's some value to store back into > > > struct integrity_inode_attributes.version. This also avoids the need = to > > > add additional storage and comparisons. > > >=20 > > > Lastly, because EVM still relies on querying and caching a backing in= ode's > > > i_version, the integrity_inode_attrs_changed() falls back to the > > > original inode.i_version !=3D cached comparison. This maintains the > > > invariant that a re-evaluation in unknown change detection circumstan= ces > > > is required. > > >=20 > > > Link: https://lore.kernel.org/all/aTspr4_h9IU4EyrR@CMGLRV3 > > > Suggested-by: Jeff Layton > > > Signed-off-by: Frederick Lawler > > > --- > > > We uncovered a case in kernels >=3D 6.13 where XFS is no longer updat= ing > > > struct kstat.change_cookie on i_op getattr() access calls. Instead, X= FS is > > > using multigrain ctime (as well as other file systems) for > > > change detection in commit 1cf7e834a6fb ("xfs: switch to > > > multigrain timestamps"). > > >=20 > > > Because file systems may implement i_version as they see fit, IMA > > > caching may be behind as well as file systems that don't support/expo= rt > > > i_version. Thus we're proposing to compare against the kstat.change_c= ookie > > > directly to the cached version, and fall back to a ctime guard when > > > that's not updated. > > >=20 > > > EVM is largely left alone since there's no trivial way to query a fil= e > > > directly in the LSM call paths to obtain kstat.change_cookie & > > > kstat.ctime to cache. Thus retains accessing i_version directly. > > >=20 > > > Regression tests will be added to the Linux Test Project instead of > > > selftest to help catch future file system changes that may impact > > > future evaluation of IMA. > > >=20 > > > I'd like this to be backported to at least 6.18 if possible. > > >=20 > > > Below is a simplified test that demonstrates the issue: > > >=20 > > > _fragment.config_ > > > CONFIG_XFS_FS=3Dy > > > CONFIG_OVERLAY_FS=3Dy > > > CONFIG_IMA=3Dy > > > CONFIG_IMA_WRITE_POLICY=3Dy > > > CONFIG_IMA_READ_POLICY=3Dy > > >=20 > > > _./test.sh_ > > >=20 > > > IMA_POLICY=3D"/sys/kernel/security/ima/policy" > > > TEST_BIN=3D"/bin/date" > > > MNT_BASE=3D"/tmp/ima_test_root" > > >=20 > > > mkdir -p "$MNT_BASE" > > > mount -t tmpfs tmpfs "$MNT_BASE" > > > mkdir -p "$MNT_BASE"/{xfs_disk,upper,work,ovl} > > >=20 > > > dd if=3D/dev/zero of=3D"$MNT_BASE/xfs.img" bs=3D1M count=3D300 > > > mkfs.xfs -q "$MNT_BASE/xfs.img" > > > mount "$MNT_BASE/xfs.img" "$MNT_BASE/xfs_disk" > > > cp "$TEST_BIN" "$MNT_BASE/xfs_disk/test_prog" > > >=20 > > > mount -t overlay overlay -o \ > > > "lowerdir=3D$MNT_BASE/xfs_disk,upperdir=3D$MNT_BASE/upper,workdir=3D$= MNT_BASE/work" \ > > > "$MNT_BASE/ovl" > > >=20 > > > echo "audit func=3DBPRM_CHECK uid=3D$(id -u nobody)" > "$IMA_POLICY" > > >=20 > > > target_prog=3D"$MNT_BASE/ovl/test_prog" > > > setpriv --reuid nobody "$target_prog" > > > setpriv --reuid nobody "$target_prog" > > > setpriv --reuid nobody "$target_prog" > > >=20 > > > audit_count=3D$(dmesg | grep -c "file=3D\"$target_prog\"") > > >=20 > > > if [[ "$audit_count" -eq 1 ]]; then > > > echo "PASS: Found exactly 1 audit event." > > > else > > > echo "FAIL: Expected 1 audit event, but found $audit_count." > > > exit 1 > > > fi > > > --- > > > Changes since RFC: > > > - Remove calls to I_IS_VERSION() > > > - Function documentation/comments > > > - Abide IMA/EVM change detection fallback invariants > > > - Combined ctime guard into version for attributes struct > > > - Link to RFC: https://lore.kernel.org/r/20251229-xfs-ima-fixup-v1-1-= 6a717c939f7c@cloudflare.com > > > --- > > > include/linux/integrity.h | 42 +++++++++++++++++++++++++++++= ++++++---- > > > security/integrity/evm/evm_main.c | 5 ++--- > > > security/integrity/ima/ima_api.c | 11 +++++++--- > > > security/integrity/ima/ima_main.c | 15 +++++--------- > > > 4 files changed, 53 insertions(+), 20 deletions(-) > > >=20 > > > diff --git a/include/linux/integrity.h b/include/linux/integrity.h > > > index f5842372359be5341b6870a43b92e695e8fc78af..5eca8aa2769f9238c68bb= 40885ecc46910524f11 100644 > > > --- a/include/linux/integrity.h > > > +++ b/include/linux/integrity.h > > > @@ -9,6 +9,7 @@ > > > =20 > > > #include > > > #include > > > +#include > > > =20 > > > enum integrity_status { > > > INTEGRITY_PASS =3D 0, > > > @@ -36,6 +37,14 @@ struct integrity_inode_attributes { > > > dev_t dev; > > > }; > > > =20 > > > +/* > > > + * Wrapper to generate an artificial version for a file. > > > + */ > > > +static inline u64 integrity_ctime_guard(struct kstat stat) > > > +{ > > > + return stat.ctime.tv_sec ^ stat.ctime.tv_nsec; > >=20 > > Unfortunately, we cannot take the risk of a collision. Better use all > > or a packed version. >=20 > Sounds good. >=20 > >=20 > > > +} > > > + > > > /* > > > * On stacked filesystems the i_version alone is not enough to detec= t file data > > > * or metadata change. Additional metadata is required. > > > @@ -51,14 +60,39 @@ integrity_inode_attrs_store(struct integrity_inod= e_attributes *attrs, > > > =20 > > > /* > > > * On stacked filesystems detect whether the inode or its content ha= s changed. > > > + * > > > + * Must be called in process context. > > > */ > > > static inline bool > > > integrity_inode_attrs_changed(const struct integrity_inode_attribute= s *attrs, > > > - const struct inode *inode) > > > + struct file *file, struct inode *inode) > > > { > > > - return (inode->i_sb->s_dev !=3D attrs->dev || > > > - inode->i_ino !=3D attrs->ino || > > > - !inode_eq_iversion(inode, attrs->version)); > > > + struct kstat stat; > > > + > > > + might_sleep(); > > > + > > > + if (inode->i_sb->s_dev !=3D attrs->dev || inode->i_ino !=3D attrs->= ino) > > > + return true; > > > + > > > + /* > > > + * EVM currently relies on backing inode i_version. While IS_I_VERS= ION > > > + * is not a good indicator of i_version support, this still retains > > > + * the logic such that a re-evaluation should still occur for EVM, = and > > > + * only for IMA if vfs_getattr_nosec() fails. > > > + */ > > > + if (!file || vfs_getattr_nosec(&file->f_path, &stat, > > > + STATX_CHANGE_COOKIE | STATX_CTIME, > > > + AT_STATX_SYNC_AS_STAT)) > > > + return !IS_I_VERSION(inode) || > > > + !inode_eq_iversion(inode, attrs->version); > > > + > > > + if (stat.result_mask & STATX_CHANGE_COOKIE) > > > + return stat.change_cookie !=3D attrs->version; > > > + > > > + if (stat.result_mask & STATX_CTIME) > > > + return integrity_ctime_guard(stat) !=3D attrs->version; > >=20 > > Yes, switching to the new field I guess it works, but I'm wondering if > > we could have more uniformity across the filesystems, otherwise one has > > to use one source for filesystem X, another source for filesystem Y. >=20 > Agreed. But I'm under the impression from casual searching, that most > file systems are likely to support ctime, than setting the change cookie > with an i_version or even having/updating i_version consistently. >=20 > Is there someone we could CC in here to get another opinion? >=20 Most filesystems properly support ctime. The problem is that only some of them (so far) have multigrain ctime support, so on many filesystems the ctime has quite coarse granularity (~1 jiffy or so). Multigrain timestamps fix that. They guarantee that if you do stat()+write()+stat() that the two stats will get different c/mtime values. This is why we've disabled reporting the i_version via - >getattr() in XFS. The ctime now provides better semantics for the change attribute on XFS. Most filesystems that support i_version now support multigrain timestamps, so I sort of expect that in the future, we may end up removing the i_version from some of these filesystems and just manufacture it from the ctime. We do need to convert more in-kernel filesystems to use multigrain timestamps first though. > >=20 > > Thanks > >=20 > > Roberto > >=20 > > > + > > > + return true; > > > } > > > =20 > > > =20 > > > diff --git a/security/integrity/evm/evm_main.c b/security/integrity/e= vm/evm_main.c > > > index 73d500a375cb37a54f295b0e1e93fd6e5d9ecddc..6a4e0e246005246d5700b= 1db590c1759242b9cb6 100644 > > > --- a/security/integrity/evm/evm_main.c > > > +++ b/security/integrity/evm/evm_main.c > > > @@ -752,9 +752,8 @@ bool evm_metadata_changed(struct inode *inode, st= ruct inode *metadata_inode) > > > bool ret =3D false; > > > =20 > > > if (iint) { > > > - ret =3D (!IS_I_VERSION(metadata_inode) || > > > - integrity_inode_attrs_changed(&iint->metadata_inode, > > > - metadata_inode)); > > > + ret =3D integrity_inode_attrs_changed(&iint->metadata_inode, > > > + NULL, metadata_inode); > > > if (ret) > > > iint->evm_status =3D INTEGRITY_UNKNOWN; > > > } > > > diff --git a/security/integrity/ima/ima_api.c b/security/integrity/im= a/ima_api.c > > > index c35ea613c9f8d404ba4886e3b736c3bab29d1668..8096986f3689781d3cdf6= 595f330033782f9cc45 100644 > > > --- a/security/integrity/ima/ima_api.c > > > +++ b/security/integrity/ima/ima_api.c > > > @@ -272,10 +272,15 @@ int ima_collect_measurement(struct ima_iint_cac= he *iint, struct file *file, > > > * to an initial measurement/appraisal/audit, but was modified to > > > * assume the file changed. > > > */ > > > - result =3D vfs_getattr_nosec(&file->f_path, &stat, STATX_CHANGE_COO= KIE, > > > + result =3D vfs_getattr_nosec(&file->f_path, &stat, > > > + STATX_CHANGE_COOKIE | STATX_CTIME, > > > AT_STATX_SYNC_AS_STAT); > > > - if (!result && (stat.result_mask & STATX_CHANGE_COOKIE)) > > > - i_version =3D stat.change_cookie; > > > + if (!result) { > > > + if (stat.result_mask & STATX_CHANGE_COOKIE) > > > + i_version =3D stat.change_cookie; > > > + else if (stat.result_mask & STATX_CTIME) > > > + i_version =3D integrity_ctime_guard(stat); > > > + } > > > hash.hdr.algo =3D algo; > > > hash.hdr.length =3D hash_digest_size[algo]; > > > =20 > > > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/i= ma/ima_main.c > > > index 5770cf691912aa912fc65280c59f5baac35dd725..3a4c32e254f925bba85cb= 91b63744ac142b3b049 100644 > > > --- a/security/integrity/ima/ima_main.c > > > +++ b/security/integrity/ima/ima_main.c > > > @@ -22,6 +22,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > #include > > > #include > > > #include > > > @@ -191,18 +192,13 @@ static void ima_check_last_writer(struct ima_ii= nt_cache *iint, > > > =20 > > > mutex_lock(&iint->mutex); > > > if (atomic_read(&inode->i_writecount) =3D=3D 1) { > > > - struct kstat stat; > > > - > > > clear_bit(IMA_EMITTED_OPENWRITERS, &iint->atomic_flags); > > > =20 > > > update =3D test_and_clear_bit(IMA_UPDATE_XATTR, > > > &iint->atomic_flags); > > > 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 !=3D iint->real_inode.version) { > > > + integrity_inode_attrs_changed(&iint->real_inode, file, > > > + inode)) { > > > iint->flags &=3D ~(IMA_DONE_MASK | IMA_NEW_FILE); > > > iint->measured_pcrs =3D 0; > > > if (update) > > > @@ -328,9 +324,8 @@ static int process_measurement(struct file *file,= const struct cred *cred, > > > real_inode =3D d_real_inode(file_dentry(file)); > > > if (real_inode !=3D inode && > > > (action & IMA_DO_MASK) && (iint->flags & IMA_DONE_MASK)) { > > > - if (!IS_I_VERSION(real_inode) || > > > - integrity_inode_attrs_changed(&iint->real_inode, > > > - real_inode)) { > > > + if (integrity_inode_attrs_changed(&iint->real_inode, > > > + file, real_inode)) { > > > iint->flags &=3D ~IMA_DONE_MASK; > > > iint->measured_pcrs =3D 0; > > > } > > >=20 > > > --- > > > base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8 > > > change-id: 20251212-xfs-ima-fixup-931780a62c2c > > >=20 > > > Best regards, > >=20 --=20 Jeff Layton