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

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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 <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: Serge Hallyn <serge@hallyn.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Mimi Zohar 2018-02-21 11:33:37 -05:00
parent d906c10d8a
commit 57b56ac6fe
2 changed files with 16 additions and 1 deletions
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2
include/linux/fs.h
View File

@ -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 {

15
security/integrity/ima/ima_appraise.c
View File

@ -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;
}