Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> writes:
> 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 named "fail_securely", which can
> be specified on the boot command line as an argument to "ima_policy=".
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:
> - Rename the builtin policy name
>
> Changelog v2:
> - address the fail safe environement
>
> Documentation/admin-guide/kernel-parameters.txt | 8 +++++++-
> security/integrity/ima/ima_appraise.c | 11 ++++++-----
> security/integrity/ima/ima_main.c | 3 ++-
> security/integrity/ima/ima_policy.c | 5 +++++
> security/integrity/integrity.h | 1 +
> 5 files changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1d1d53f85ddd..2cc17dc7ab84 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 |
> + fail_securely"
>
> 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 "fail_securely" policy forces file signature
> + verification failure also 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 4bafb397ee91..3034935e1eb3 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -304,12 +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)) ==
> - (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..36f9570941c1 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, "fail_securely") == 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)
