Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> writes:
> 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.
Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
>
> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
> Cc: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Dongsu Park <dongsu@xxxxxxxxxx>
> Cc: Alban Crequy <alban@xxxxxxxxxx>
> Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
>
> ---
> 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)) {
> + 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;
> }
