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Hallyn" , linux-security-module@vger.kernel.org (open list:SECURITY SUBSYSTEM), linux-kernel@vger.kernel.org (open list) Subject: [PATCH v3] ima: don't clear IMA_DIGSIG flag when setting or removing non-IMA xattr Date: Mon, 15 Sep 2025 13:55:23 +0800 Message-ID: <20250915055524.2187783-1-coxu@redhat.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250902042515.759750-1-coxu@redhat.com> References: <20250902042515.759750-1-coxu@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently when both IMA and EVM are in fix mode, the IMA signature will be reset to IMA hash if a program first stores IMA signature in security.ima and then writes/removes some other security xattr for the file. For example, on Fedora, after booting the kernel with "ima_appraise=3Dfix evm=3Dfix ima_policy=3Dappraise_tcb" and installing rpm-plugin-ima, installing/reinstalling a package will not make good reference IMA signature generated. Instead IMA hash is generated, # getfattr -m - -d -e hex /usr/bin/bash # file: usr/bin/bash security.ima=3D0x0404... This happens because when setting security.selinux, the IMA_DIGSIG flag that had been set early was cleared. As a result, IMA hash is generated when the file is closed. Similarly, IMA signature can be cleared on file close after removing security xattr like security.evm or setting/removing ACL. Prevent replacing the IMA file signature with a file hash, by preventing the IMA_DIGSIG flag from being reset. Here's a minimal C reproducer which sets security.selinux as the last step which can also replaced by removing security.evm or setting ACL, #include #include #include #include #include #include int main() { const char* file_path =3D "/usr/sbin/test_binary"; const char* hex_string =3D "030204d33204490066306402304"; int length =3D strlen(hex_string); char* ima_attr_value; int fd; fd =3D open(file_path, O_WRONLY|O_CREAT|O_EXCL, 0644); if (fd =3D=3D -1) { perror("Error opening file"); return 1; } ima_attr_value =3D (char*)malloc(length / 2 ); for (int i =3D 0, j =3D 0; i < length; i +=3D 2, j++) { sscanf(hex_string + i, "%2hhx", &ima_attr_value[j]); } if (fsetxattr(fd, "security.ima", ima_attr_value, length/2, 0) =3D= =3D -1) { perror("Error setting extended attribute"); close(fd); return 1; } const char* selinux_value=3D "system_u:object_r:bin_t:s0"; if (fsetxattr(fd, "security.selinux", selinux_value, strlen(selinux= _value), 0) =3D=3D -1) { perror("Error setting extended attribute"); close(fd); return 1; } close(fd); return 0; } Signed-off-by: Coiby Xu --- security/integrity/ima/ima_appraise.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima= /ima_appraise.c index f435eff4667f..5149ff4fd50d 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -694,6 +694,15 @@ static int ima_protect_xattr(struct dentry *dentry, co= nst char *xattr_name, return 0; } =20 +/* + * ima_reset_appraise_flags - reset ima_iint_cache flags + * + * @digsig: whether to clear/set IMA_DIGSIG flag, tristate values + * 0: clear IMA_DIGSIG + * 1: set IMA_DIGSIG + * -1: don't change IMA_DIGSIG + * + */ static void ima_reset_appraise_flags(struct inode *inode, int digsig) { struct ima_iint_cache *iint; @@ -706,9 +715,9 @@ static void ima_reset_appraise_flags(struct inode *inod= e, int digsig) return; iint->measured_pcrs =3D 0; set_bit(IMA_CHANGE_XATTR, &iint->atomic_flags); - if (digsig) + if (digsig =3D=3D 1) set_bit(IMA_DIGSIG, &iint->atomic_flags); - else + else if (digsig =3D=3D 0) clear_bit(IMA_DIGSIG, &iint->atomic_flags); } =20 @@ -794,6 +803,8 @@ static int ima_inode_setxattr(struct mnt_idmap *idmap, = struct dentry *dentry, digsig =3D (xvalue->type =3D=3D EVM_IMA_XATTR_DIGSIG); } else if (!strcmp(xattr_name, XATTR_NAME_EVM) && xattr_value_len > 0) { digsig =3D (xvalue->type =3D=3D EVM_XATTR_PORTABLE_DIGSIG); + } else { + digsig =3D -1; } if (result =3D=3D 1 || evm_revalidate_status(xattr_name)) { ima_reset_appraise_flags(d_backing_inode(dentry), digsig); @@ -807,7 +818,7 @@ static int ima_inode_set_acl(struct mnt_idmap *idmap, s= truct dentry *dentry, const char *acl_name, struct posix_acl *kacl) { if (evm_revalidate_status(acl_name)) - ima_reset_appraise_flags(d_backing_inode(dentry), 0); + ima_reset_appraise_flags(d_backing_inode(dentry), -1); =20 return 0; } @@ -815,11 +826,13 @@ static int ima_inode_set_acl(struct mnt_idmap *idmap,= struct dentry *dentry, static int ima_inode_removexattr(struct mnt_idmap *idmap, struct dentry *d= entry, const char *xattr_name) { - int result; + int result, digsig =3D -1; =20 result =3D ima_protect_xattr(dentry, xattr_name, NULL, 0); if (result =3D=3D 1 || evm_revalidate_status(xattr_name)) { - ima_reset_appraise_flags(d_backing_inode(dentry), 0); + if (!strcmp(xattr_name, XATTR_NAME_IMA)) + digsig =3D 0; + ima_reset_appraise_flags(d_backing_inode(dentry), digsig); if (result =3D=3D 1) result =3D 0; } base-commit: 7aac71907bdea16e2754a782b9d9155449a9d49d --=20 2.51.0