On Tue, 2018-02-27 at 16:35 -0600, Serge E. Hallyn wrote:
> Quoting Mimi Zohar (zohar@xxxxxxxxxxxxxxxxxx):
> > This patch addresses the fuse privileged mounted filesystems in
> > environments which are unwilling to accept the risk of trusting the
> > signature verification and want to always fail safe, but are for
> > example using a pre-built kernel.
> >
> > This patch defines a new builtin policy "unverifiable_sigs", which can
>
> How about recalc_unverifiable_sigs?
Cute, I really like that name, but in this case we're failing the
signature verification.
> It's long, but unverifiable_sigs
> is not clear about whether the intent is to accept or recalculate them.
>
> (or fail_unverifiable_sigs like the flag)
Could we abbreviate it to "fail_usigs"? Or perhaps allow both
"fail_unverifiable_sigs" and "fail_usigs".
Mimi
>
> > be specified on the boot command line as an argument to "ima_policy=".
> >
> > 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 v2:
> > - address the fail safe environement
> > ---
> > Documentation/admin-guide/kernel-parameters.txt | 8 +++++++-
> > security/integrity/ima/ima_appraise.c | 10 ++++++----
> > security/integrity/ima/ima_main.c | 3 ++-
> > security/integrity/ima/ima_policy.c | 5 +++++
> > security/integrity/integrity.h | 1 +
> > 5 files changed, 21 insertions(+), 6 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 1d1d53f85ddd..c655cd8dbaa0 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -1525,7 +1525,8 @@
> >
> > ima_policy= [IMA]
> > The builtin policies to load during IMA setup.
> > - Format: "tcb | appraise_tcb | secure_boot"
> > + Format: "tcb | appraise_tcb | secure_boot |
> > + unverifiable_sigs"
> >
> > The "tcb" policy measures all programs exec'd, files
> > mmap'd for exec, and all files opened with the read
> > @@ -1540,6 +1541,11 @@
> > of files (eg. kexec kernel image, kernel modules,
> > firmware, policy, etc) based on file signatures.
> >
> > + The "unverifiable_sigs" policy forces file signature
> > + verification failure on privileged mounted
> > + filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
> > + flag.
> > +
> > ima_tcb [IMA] Deprecated. Use ima_policy= instead.
> > Load a policy which meets the needs of the Trusted
> > Computing Base. This means IMA will measure all
> > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> > index f34901069e78..3034935e1eb3 100644
> > --- a/security/integrity/ima/ima_appraise.c
> > +++ b/security/integrity/ima/ima_appraise.c
> > @@ -304,11 +304,13 @@ int ima_appraise_measurement(enum ima_hooks func,
> > out:
> > /*
> > * 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.
> > + * On these filesytems, that are mounted by an untrusted mounter or
> > + * for systems not willing to accept the risk, fail the file signature
> > + * verification.
> > */
> > - if (inode->i_sb->s_iflags &
> > - (SB_I_IMA_UNVERIFIABLE_SIGNATURE | SB_I_UNTRUSTED_MOUNTER)) {
> > + if ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
> > + ((inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) ||
> > + (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) {
> > status = INTEGRITY_FAIL;
> > cause = "unverifiable-signature";
> > integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
> > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> > index f550f25294a3..5d122daf5c8a 100644
> > --- a/security/integrity/ima/ima_main.c
> > +++ b/security/integrity/ima/ima_main.c
> > @@ -238,7 +238,8 @@ static int process_measurement(struct file *file, const struct cred *cred,
> > */
> > if (test_and_clear_bit(IMA_CHANGE_XATTR, &iint->atomic_flags) ||
> > ((inode->i_sb->s_iflags & SB_I_IMA_UNVERIFIABLE_SIGNATURE) &&
> > - !(inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER))) {
> > + !(inode->i_sb->s_iflags & SB_I_UNTRUSTED_MOUNTER) &&
> > + !(action & IMA_FAIL_UNVERIFIABLE_SIGS))) {
> > iint->flags &= ~IMA_DONE_MASK;
> > iint->measured_pcrs = 0;
> > }
> > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> > index e3da29af2c16..ead3f7fe6998 100644
> > --- a/security/integrity/ima/ima_policy.c
> > +++ b/security/integrity/ima/ima_policy.c
> > @@ -188,6 +188,7 @@ __setup("ima_tcb", default_measure_policy_setup);
> >
> > static bool ima_use_appraise_tcb __initdata;
> > static bool ima_use_secure_boot __initdata;
> > +static bool ima_fail_unverifiable_sigs __ro_after_init;
> > static int __init policy_setup(char *str)
> > {
> > char *p;
> > @@ -201,6 +202,8 @@ static int __init policy_setup(char *str)
> > ima_use_appraise_tcb = true;
> > else if (strcmp(p, "secure_boot") == 0)
> > ima_use_secure_boot = true;
> > + else if (strcmp(p, "unverifiable_sigs") == 0)
> > + ima_fail_unverifiable_sigs = true;
> > }
> >
> > return 1;
> > @@ -390,6 +393,8 @@ int ima_match_policy(struct inode *inode, const struct cred *cred, u32 secid,
> > if (entry->action & IMA_APPRAISE) {
> > action |= get_subaction(entry, func);
> > action ^= IMA_HASH;
> > + if (ima_fail_unverifiable_sigs)
> > + action |= IMA_FAIL_UNVERIFIABLE_SIGS;
> > }
> >
> > if (entry->action & IMA_DO_MASK)
> > diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
> > index 843ae23ba0ac..8224880935e0 100644
> > --- a/security/integrity/integrity.h
> > +++ b/security/integrity/integrity.h
> > @@ -35,6 +35,7 @@
> > #define IMA_PERMIT_DIRECTIO 0x02000000
> > #define IMA_NEW_FILE 0x04000000
> > #define EVM_IMMUTABLE_DIGSIG 0x08000000
> > +#define IMA_FAIL_UNVERIFIABLE_SIGS 0x10000000
> >
> > #define IMA_DO_MASK (IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \
> > IMA_HASH | IMA_APPRAISE_SUBMASK)
> > --
> > 2.7.5
>
