From mboxrd@z Thu Jan 1 00:00:00 1970 From: serge@hallyn.com (Serge E. Hallyn) Date: Mon, 12 Mar 2018 14:17:46 -0500 Subject: [PATCH v3 1/4] ima: fail file signature verification on non-init mounted filesystems In-Reply-To: <1520540650-7451-2-git-send-email-zohar@linux.vnet.ibm.com> References: <1520540650-7451-1-git-send-email-zohar@linux.vnet.ibm.com> <1520540650-7451-2-git-send-email-zohar@linux.vnet.ibm.com> Message-ID: <20180312191745.GA29878@mail.hallyn.com> To: linux-security-module@vger.kernel.org List-Id: linux-security-module.vger.kernel.org Quoting Mimi Zohar (zohar at linux.vnet.ibm.com): > FUSE can be mounted by unprivileged users either today with fusermount > installed with setuid, or soon with the upcoming patches to allow FUSE > mounts in a non-init user namespace. > > This patch addresses the new unprivileged non-init mounted filesystems, > which are untrusted, by failing the signature verification. > > This patch defines two new flags SB_I_IMA_UNVERIFIABLE_SIGNATURE and > SB_I_UNTRUSTED_MOUNTER. > > Signed-off-by: Mimi Zohar > Cc: Miklos Szeredi > Cc: Seth Forshee > Cc: Eric W. Biederman > Cc: Dongsu Park > Cc: Alban Crequy > Cc: Serge E. Hallyn Acked-by: Serge Hallyn One comment below though, > > --- > Changelog v3: > - Fix SB_IMA_UNVERIFIABLE_SIGNATURE & SB_I_UNTRUSTED_MOUNTER test. > > Changelog v2: > - Limit patch to non-init mounted filesystems. > - Define 2 sb->s_iflags > > Changelog v1: > - Merged the unprivileged and privileged patches. > - Dropped IMA fsname support. > - Introduced a new IMA builtin policy named "untrusted_fs". > - Replaced fs_type flag with sb->s_iflags flag. > > include/linux/fs.h | 2 ++ > security/integrity/ima/ima_appraise.c | 15 ++++++++++++++- > 2 files changed, 16 insertions(+), 1 deletion(-) > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 2a815560fda0..4e1c76af7b68 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -1320,6 +1320,8 @@ extern int send_sigurg(struct fown_struct *fown); > > /* sb->s_iflags to limit user namespace mounts */ > #define SB_I_USERNS_VISIBLE 0x00000010 /* fstype already mounted */ > +#define SB_I_IMA_UNVERIFIABLE_SIGNATURE 0x00000020 > +#define SB_I_UNTRUSTED_MOUNTER 0x00000040 > > /* Possible states of 'frozen' field */ > enum { > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c > index 1b177461f20e..4bafb397ee91 100644 > --- a/security/integrity/ima/ima_appraise.c > +++ b/security/integrity/ima/ima_appraise.c > @@ -302,7 +302,19 @@ int ima_appraise_measurement(enum ima_hooks func, > } > > out: > - if (status != INTEGRITY_PASS) { > + /* > + * File signatures on some filesystems can not be properly verified. > + * On these filesytems, that are mounted by an untrusted mounter, > + * fail the file signature verification. > + */ > + if ((inode->i_sb->s_iflags & > + (SB_I_IMA_UNVERIFIABLE_SIGNATURE | SB_I_UNTRUSTED_MOUNTER)) == > + (SB_I_IMA_UNVERIFIABLE_SIGNATURE | SB_I_UNTRUSTED_MOUNTER)) { Heh, this is misleading combination of parentheses and indentation :) I would recommend using a temporary variable like: cmpflags = SB_I_IMA_UNVERIFIABLE_SIGNATURE | SB_I_UNTRUSTED_MOUNTER; if ((inode->i_sb->s_iflags & cmpflags) == cmpflags) { or maybe a helper function. > + status = INTEGRITY_FAIL; > + cause = "unverifiable-signature"; > + integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename, > + op, cause, rc, 0); > + } else if (status != INTEGRITY_PASS) { > if ((ima_appraise & IMA_APPRAISE_FIX) && > (!xattr_value || > xattr_value->type != EVM_IMA_XATTR_DIGSIG)) { > @@ -319,6 +331,7 @@ int ima_appraise_measurement(enum ima_hooks func, > } else { > ima_cache_flags(iint, func); > } > + > ima_set_cache_status(iint, func, status); > return status; > } > -- > 2.7.5 -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html