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Thu, 12 Oct 2023 13:25:01 +0000 (GMT) Message-ID: <84cfe4d93cb5b02591f4bd921b828eb6f3e95faa.camel@linux.ibm.com> Subject: Re: [PATCH v3 02/25] ima: Align ima_post_path_mknod() definition with LSM infrastructure From: Mimi Zohar To: Roberto Sassu , viro@zeniv.linux.org.uk, brauner@kernel.org, chuck.lever@oracle.com, jlayton@kernel.org, neilb@suse.de, kolga@netapp.com, Dai.Ngo@oracle.com, tom@talpey.com, dmitry.kasatkin@gmail.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, dhowells@redhat.com, jarkko@kernel.org, stephen.smalley.work@gmail.com, eparis@parisplace.org, casey@schaufler-ca.com Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, keyrings@vger.kernel.org, selinux@vger.kernel.org, Roberto Sassu Date: Thu, 12 Oct 2023 09:25:00 -0400 In-Reply-To: <2336abd6ae195eda221d54e3c2349a4760afaff2.camel@huaweicloud.com> References: <20230904133415.1799503-1-roberto.sassu@huaweicloud.com> <20230904133415.1799503-3-roberto.sassu@huaweicloud.com> <8646e30b0074a2932076b5a0a792b14be034de98.camel@linux.ibm.com> <16c8c95f2e63ab9a2fba8cba919bf129d0541b61.camel@huaweicloud.com> <2336abd6ae195eda221d54e3c2349a4760afaff2.camel@huaweicloud.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.28.5 (3.28.5-22.el8) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 3O5zaE-jKMy0v3K8bSHmEwYSbhvfpYCS X-Proofpoint-GUID: m8ZqZUL2g5V8V5rT8_Mbj_JZVELiLoiS X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-10-12_05,2023-10-12_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 bulkscore=0 spamscore=0 phishscore=0 malwarescore=0 suspectscore=0 adultscore=0 priorityscore=1501 mlxscore=0 mlxlogscore=999 lowpriorityscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2309180000 definitions=main-2310120110 X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Thu, 2023-10-12 at 14:19 +0200, Roberto Sassu wrote: > On Thu, 2023-10-12 at 07:42 -0400, Mimi Zohar wrote: > > On Thu, 2023-10-12 at 09:29 +0200, Roberto Sassu wrote: > > > On Wed, 2023-10-11 at 15:01 -0400, Mimi Zohar wrote: > > > > On Wed, 2023-10-11 at 18:02 +0200, Roberto Sassu wrote: > > > > > On Wed, 2023-10-11 at 10:38 -0400, Mimi Zohar wrote: > > > > > > On Mon, 2023-09-04 at 15:33 +0200, Roberto Sassu wrote: > > > > > > > From: Roberto Sassu > > > > > > > > > > > > > > Change ima_post_path_mknod() definition, so that it can be registered as > > > > > > > implementation of the path_post_mknod hook. Since LSMs see a umask-stripped > > > > > > > mode from security_path_mknod(), pass the same to ima_post_path_mknod() as > > > > > > > well. > > > > > > > Also, make sure that ima_post_path_mknod() is executed only if > > > > > > > (mode & S_IFMT) is equal to zero or S_IFREG. > > > > > > > > > > > > > > Add this check to take into account the different placement of the > > > > > > > path_post_mknod hook (to be introduced) in do_mknodat(). > > > > > > > > > > > > Move "(to be introduced)" to when it is first mentioned. > > > > > > > > > > > > > Since the new hook > > > > > > > will be placed after the switch(), the check ensures that > > > > > > > ima_post_path_mknod() is invoked as originally intended when it is > > > > > > > registered as implementation of path_post_mknod. > > > > > > > > > > > > > > Signed-off-by: Roberto Sassu > > > > > > > --- > > > > > > > fs/namei.c | 9 ++++++--- > > > > > > > include/linux/ima.h | 7 +++++-- > > > > > > > security/integrity/ima/ima_main.c | 10 +++++++++- > > > > > > > 3 files changed, 20 insertions(+), 6 deletions(-) > > > > > > > > > > > > > > diff --git a/fs/namei.c b/fs/namei.c > > > > > > > index e56ff39a79bc..c5e96f716f98 100644 > > > > > > > --- a/fs/namei.c > > > > > > > +++ b/fs/namei.c > > > > > > > @@ -4024,6 +4024,7 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode, > > > > > > > struct path path; > > > > > > > int error; > > > > > > > unsigned int lookup_flags = 0; > > > > > > > + umode_t mode_stripped; > > > > > > > > > > > > > > error = may_mknod(mode); > > > > > > > if (error) > > > > > > > @@ -4034,8 +4035,9 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode, > > > > > > > if (IS_ERR(dentry)) > > > > > > > goto out1; > > > > > > > > > > > > > > - error = security_path_mknod(&path, dentry, > > > > > > > - mode_strip_umask(path.dentry->d_inode, mode), dev); > > > > > > > + mode_stripped = mode_strip_umask(path.dentry->d_inode, mode); > > > > > > > + > > > > > > > + error = security_path_mknod(&path, dentry, mode_stripped, dev); > > > > > > > if (error) > > > > > > > goto out2; > > > > > > > > > > > > > > @@ -4045,7 +4047,8 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode, > > > > > > > error = vfs_create(idmap, path.dentry->d_inode, > > > > > > > dentry, mode, true); > > > > > > > if (!error) > > > > > > > - ima_post_path_mknod(idmap, dentry); > > > > > > > + ima_post_path_mknod(idmap, &path, dentry, > > > > > > > + mode_stripped, dev); > > > > > > > break; > > > > > > > case S_IFCHR: case S_IFBLK: > > > > > > > error = vfs_mknod(idmap, path.dentry->d_inode, > > > > > > > diff --git a/include/linux/ima.h b/include/linux/ima.h > > > > > > > index 910a2f11a906..179ce52013b2 100644 > > > > > > > --- a/include/linux/ima.h > > > > > > > +++ b/include/linux/ima.h > > > > > > > @@ -32,7 +32,8 @@ extern int ima_read_file(struct file *file, enum kernel_read_file_id id, > > > > > > > extern int ima_post_read_file(struct file *file, void *buf, loff_t size, > > > > > > > enum kernel_read_file_id id); > > > > > > > extern void ima_post_path_mknod(struct mnt_idmap *idmap, > > > > > > > - struct dentry *dentry); > > > > > > > + const struct path *dir, struct dentry *dentry, > > > > > > > + umode_t mode, unsigned int dev); > > > > > > > extern int ima_file_hash(struct file *file, char *buf, size_t buf_size); > > > > > > > extern int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size); > > > > > > > extern void ima_kexec_cmdline(int kernel_fd, const void *buf, int size); > > > > > > > @@ -114,7 +115,9 @@ static inline int ima_post_read_file(struct file *file, void *buf, loff_t size, > > > > > > > } > > > > > > > > > > > > > > static inline void ima_post_path_mknod(struct mnt_idmap *idmap, > > > > > > > - struct dentry *dentry) > > > > > > > + const struct path *dir, > > > > > > > + struct dentry *dentry, > > > > > > > + umode_t mode, unsigned int dev) > > > > > > > { > > > > > > > return; > > > > > > > } > > > > > > > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c > > > > > > > index 365db0e43d7c..76eba92d7f10 100644 > > > > > > > --- a/security/integrity/ima/ima_main.c > > > > > > > +++ b/security/integrity/ima/ima_main.c > > > > > > > @@ -696,18 +696,26 @@ void ima_post_create_tmpfile(struct mnt_idmap *idmap, > > > > > > > /** > > > > > > > * ima_post_path_mknod - mark as a new inode > > > > > > > * @idmap: idmap of the mount the inode was found from > > > > > > > + * @dir: path structure of parent of the new file > > > > > > > * @dentry: newly created dentry > > > > > > > + * @mode: mode of the new file > > > > > > > + * @dev: undecoded device number > > > > > > > * > > > > > > > * Mark files created via the mknodat syscall as new, so that the > > > > > > > * file data can be written later. > > > > > > > */ > > > > > > > void ima_post_path_mknod(struct mnt_idmap *idmap, > > > > > > > - struct dentry *dentry) > > > > > > > + const struct path *dir, struct dentry *dentry, > > > > > > > + umode_t mode, unsigned int dev) > > > > > > > { > > > > > > > struct integrity_iint_cache *iint; > > > > > > > struct inode *inode = dentry->d_inode; > > > > > > > int must_appraise; > > > > > > > > > > > > > > + /* See do_mknodat(), IMA is executed for case 0: and case S_IFREG: */ > > > > > > > + if ((mode & S_IFMT) != 0 && (mode & S_IFMT) != S_IFREG) > > > > > > > + return; > > > > > > > + > > > > > > > > > > > > There's already a check below to make sure that this is a regular file. > > > > > > Are both needed? > > > > > > > > > > You are right, I can remove the first check. > > > > > > > > The question then becomes why modify hook the arguments? > > > > > > We need to make sure that ima_post_path_mknod() has the same parameters > > > as the LSM hook at the time we register it to the LSM infrastructure. > > > > I'm trying to understand why the pre hook parameters and the missing > > IMA parameter are used, as opposed to just defining the new > > post_path_mknod hook like IMA. > > As an empyrical rule, I pass the same parameters as the corresponding > pre hook (plus idmap, in this case). This is similar to the > inode_setxattr hook. But I can be wrong, if desired I can reduce. The inode_setxattr hook change example is legitimate, as EVM includes idmap, while IMA doesn't. Unless there is a good reason for the additional parameters, I'm not sure that adding them makes sense. Not modifying the parameter list will reduce the size of this patch set. -- thanks, Mimi