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: 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>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c6baf76..d9e6082 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1321,6 +1321,8 @@
/* 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 1b17746..4bafb39 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -302,7 +302,19 @@
}
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 @@
} else {
ima_cache_flags(iint, func);
}
+
ima_set_cache_status(iint, func, status);
return status;
}