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Thu, 6 Apr 2023 16:10:05 +0000 (GMT) Message-ID: Date: Thu, 6 Apr 2023 12:10:05 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH] overlayfs: Trigger file re-evaluation by IMA / EVM after writes Content-Language: en-US To: Paul Moore Cc: Christian Brauner , zohar@linux.ibm.com, linux-integrity@vger.kernel.org, miklos@szeredi.hu, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org, amir73il@gmail.com References: <20230405171449.4064321-1-stefanb@linux.ibm.com> <20230406-diffamieren-langhaarig-87511897e77d@brauner> From: Stefan Berger In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: MV4lEkvse16aqDIDhTP18FyS6RFkpIMQ X-Proofpoint-ORIG-GUID: nxsYdAQTmibWu6xHKkQlJ-xBymrZVnNT X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-04-06_09,2023-04-06_03,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 bulkscore=0 suspectscore=0 adultscore=0 lowpriorityscore=0 malwarescore=0 clxscore=1015 priorityscore=1501 mlxscore=0 mlxlogscore=999 impostorscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303200000 definitions=main-2304060143 Precedence: bulk List-ID: On 4/6/23 10:36, Paul Moore wrote: > On Thu, Apr 6, 2023 at 10:20 AM Stefan Berger wrote: >> On 4/6/23 10:05, Paul Moore wrote: >>> On Thu, Apr 6, 2023 at 6:26 AM Christian Brauner wrote: >>>> On Wed, Apr 05, 2023 at 01:14:49PM -0400, Stefan Berger wrote: >>>>> Overlayfs fails to notify IMA / EVM about file content modifications >>>>> and therefore IMA-appraised files may execute even though their file >>>>> signature does not validate against the changed hash of the file >>>>> anymore. To resolve this issue, add a call to integrity_notify_change() >>>>> to the ovl_release() function to notify the integrity subsystem about >>>>> file changes. The set flag triggers the re-evaluation of the file by >>>>> IMA / EVM once the file is accessed again. >>>>> >>>>> Signed-off-by: Stefan Berger >>>>> --- >>>>> fs/overlayfs/file.c | 4 ++++ >>>>> include/linux/integrity.h | 6 ++++++ >>>>> security/integrity/iint.c | 13 +++++++++++++ >>>>> 3 files changed, 23 insertions(+) >>>>> >>>>> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c >>>>> index 6011f955436b..19b8f4bcc18c 100644 >>>>> --- a/fs/overlayfs/file.c >>>>> +++ b/fs/overlayfs/file.c >>>>> @@ -13,6 +13,7 @@ >>>>> #include >>>>> #include >>>>> #include >>>>> +#include >>>>> #include "overlayfs.h" >>>>> >>>>> struct ovl_aio_req { >>>>> @@ -169,6 +170,9 @@ static int ovl_open(struct inode *inode, struct file *file) >>>>> >>>>> static int ovl_release(struct inode *inode, struct file *file) >>>>> { >>>>> + if (file->f_flags & O_ACCMODE) >>>>> + integrity_notify_change(inode); >>>>> + >>>>> fput(file->private_data); >>>>> >>>>> return 0; >>>>> diff --git a/include/linux/integrity.h b/include/linux/integrity.h >>>>> index 2ea0f2f65ab6..cefdeccc1619 100644 >>>>> --- a/include/linux/integrity.h >>>>> +++ b/include/linux/integrity.h >>>>> @@ -23,6 +23,7 @@ enum integrity_status { >>>>> #ifdef CONFIG_INTEGRITY >>>>> extern struct integrity_iint_cache *integrity_inode_get(struct inode *inode); >>>>> extern void integrity_inode_free(struct inode *inode); >>>>> +extern void integrity_notify_change(struct inode *inode); >>>> >>>> I thought we concluded that ima is going to move into the security hook >>>> infrastructure so it seems this should be a proper LSM hook? >>> >>> We are working towards migrating IMA/EVM to the LSM layer, but there >>> are a few things we need to fix/update/remove first; if anyone is >>> curious, you can join the LSM list as we've been discussing some of >>> these changes this week. Bug fixes like this should probably remain >>> as IMA/EVM calls for the time being, with the understanding that they >>> will migrate over with the rest of IMA/EVM. >>> >>> That said, we should give Mimi a chance to review this patch as it is >>> possible there is a different/better approach. A bit of patience may >>> be required as I know Mimi is very busy at the moment. >> >> There may be a better approach actually by increasing the inode's i_version, >> which then should trigger the appropriate path in ima_check_last_writer(). > > I'm not the VFS/inode expert here, but I thought the inode's i_version > field was only supposed to be bumped when the inode metadata changed, > not necessarily the file contents, right? > > That said, overlayfs is a bit different so maybe that's okay, but I > think we would need to hear from the VFS folks if this is acceptable. > Exactly. In ima_check_last_writer() I want to trigger the code path with iint->flags &= ... if (atomic_read(&inode->i_writecount) == 1) { 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)) { iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE); iint->measured_pcrs = 0; if (update) ima_update_xattr(iint, file); } } This patch here resolves it for my use case and triggers the expected code paths when ima_file_free() -> ima_check_last_writer() is called because then the i_version is seen as having been modified. diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c index 6011f955436b..1dfe5e7bfe1c 100644 --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -13,6 +13,7 @@ #include #include #include +#include #include "overlayfs.h" struct ovl_aio_req { @@ -408,6 +409,8 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter) if (ret != -EIOCBQUEUED) ovl_aio_cleanup_handler(aio_req); } + if (ret > 0) + inode_maybe_inc_iversion(inode, false); out: revert_creds(old_cred); out_fdput: I have been testing this in a OpenBMC/Yocto environment where overlayfs is used as root filesystem with the lower filesystem being a squashfs. Regards, Stefan