Commit 57b56ac6 authored by Mimi Zohar's avatar Mimi Zohar
Browse files

ima: fail file signature verification on non-init mounted filesystems 



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: default avatarMimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Seth Forshee <seth.forshee@canonical.com>
Cc: Dongsu Park <dongsu@kinvolk.io>
Cc: Alban Crequy <alban@kinvolk.io>
Acked-by: default avatarSerge Hallyn <serge@hallyn.com>
Acked-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent d906c10d

include/linux/fs.h

+2 −0
Original line number Diff line number Diff line
@@ -1321,6 +1321,8 @@ 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 {

security/integrity/ima/ima_appraise.c

+14 −1
Original line number Diff line number Diff line
@@ -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)) {

		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 @@ out: 
	} else {

		ima_cache_flags(iint, func);

	}



	ima_set_cache_status(iint, func, status);

	return status;

}

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