* [RFC][PATCH] apparmor: Enforce progressively tighter permissions for no_new_privs
@ 2021-01-20 21:26 Eric W. Biederman
2021-01-20 21:38 ` Eric W. Biederman
2021-01-20 22:32 ` John Johansen
0 siblings, 2 replies; 5+ messages in thread
From: Eric W. Biederman @ 2021-01-20 21:26 UTC (permalink / raw)
To: linux-security-module
Cc: Andy Lutomirski, Kees Cook, James Morris, John Johansen,
apparmor, linux-kernel, Linus Torvalds
The current understanding of apparmor with respect to no_new_privs is at
odds with how no_new_privs is implemented and understood by the rest of
the kernel.
The documentation of no_new_privs states:
> With ``no_new_privs`` set, ``execve()`` promises not to grant the
> privilege to do anything that could not have been done without the
> execve call.
And reading through the kernel except for apparmor that description
matches what is implemented.
There are two major divergences of apparmor from this definition:
- proc_setattr enforces limitations when no_new_privs are set.
- the limitation is enforced from the apparent time when no_new_privs is
set instead of guaranteeing that each execve has progressively more
narrow permissions.
The code in apparmor that attempts to discover the apparmor label at the
point where no_new_privs is set is not robust. The capture happens a
long time after no_new_privs is set.
Capturing the label at the point where no_new_privs is set is
practically impossible to implement robustly. Today the rule is struct
cred can only be changed by it's current task. Today
SECCOMP_FILTER_FLAG_TSYNC sets no_new_privs from another thread. A
robust implementation would require changing something fundamental in
how creds are managed for SECCOMP_FILTER_FLAG_TSYNC to be able to
capture the cred at the point it is set.
Futhermore given the consistent documentation and how everything else
implements no_new_privs, not having the permissions get progressively
tighter is a footgun aimed at userspace. I fully expect it to break any
security sensitive software that uses no_new_privs and was not
deliberately designed and tested against apparmor.
Avoid the questionable and hard to fix implementation and the
potential to confuse userspace by having no_new_privs enforce
progressinvely tighter permissions.
Fixes: 9fcf78cca198 ("apparmor: update domain transitions that are subsets of confinement at nnp")
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
I came accross this while examining the places cred_guard_mutex is
used and trying to find a way to make those code paths less insane.
If it would be more pallatable I would not mind removing the
task_no_new_privs test entirely from aa_change_hat and aa_change_profile
as those are not part of exec, so arguably no_new_privs should not care
about them at all.
Can we please get rid of the huge semantic wart and pain in the implementation?
security/apparmor/domain.c | 39 ++++----------------------------
security/apparmor/include/task.h | 4 ----
security/apparmor/task.c | 7 ------
3 files changed, 4 insertions(+), 46 deletions(-)
diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
index f919ebd042fd..8f77059bf890 100644
--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -869,17 +869,6 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
label = aa_get_newest_label(cred_label(bprm->cred));
- /*
- * Detect no new privs being set, and store the label it
- * occurred under. Ideally this would happen when nnp
- * is set but there isn't a good way to do that yet.
- *
- * Testing for unconfined must be done before the subset test
- */
- if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) && !unconfined(label) &&
- !ctx->nnp)
- ctx->nnp = aa_get_label(label);
-
/* buffer freed below, name is pointer into buffer */
buffer = aa_get_buffer(false);
if (!buffer) {
@@ -915,7 +904,7 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
*/
if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) &&
!unconfined(label) &&
- !aa_label_is_unconfined_subset(new, ctx->nnp)) {
+ !aa_label_is_unconfined_subset(new, label)) {
error = -EPERM;
info = "no new privs";
goto audit;
@@ -1158,16 +1147,6 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
label = aa_get_newest_cred_label(cred);
previous = aa_get_newest_label(ctx->previous);
- /*
- * Detect no new privs being set, and store the label it
- * occurred under. Ideally this would happen when nnp
- * is set but there isn't a good way to do that yet.
- *
- * Testing for unconfined must be done before the subset test
- */
- if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
- ctx->nnp = aa_get_label(label);
-
if (unconfined(label)) {
info = "unconfined can not change_hat";
error = -EPERM;
@@ -1193,7 +1172,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
* reduce restrictions.
*/
if (task_no_new_privs(current) && !unconfined(label) &&
- !aa_label_is_unconfined_subset(new, ctx->nnp)) {
+ !aa_label_is_unconfined_subset(new, label)) {
/* not an apparmor denial per se, so don't log it */
AA_DEBUG("no_new_privs - change_hat denied");
error = -EPERM;
@@ -1214,7 +1193,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
* reduce restrictions.
*/
if (task_no_new_privs(current) && !unconfined(label) &&
- !aa_label_is_unconfined_subset(previous, ctx->nnp)) {
+ !aa_label_is_unconfined_subset(previous, label)) {
/* not an apparmor denial per se, so don't log it */
AA_DEBUG("no_new_privs - change_hat denied");
error = -EPERM;
@@ -1303,16 +1282,6 @@ int aa_change_profile(const char *fqname, int flags)
label = aa_get_current_label();
- /*
- * Detect no new privs being set, and store the label it
- * occurred under. Ideally this would happen when nnp
- * is set but there isn't a good way to do that yet.
- *
- * Testing for unconfined must be done before the subset test
- */
- if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
- ctx->nnp = aa_get_label(label);
-
if (!fqname || !*fqname) {
aa_put_label(label);
AA_DEBUG("no profile name");
@@ -1409,7 +1378,7 @@ int aa_change_profile(const char *fqname, int flags)
* reduce restrictions.
*/
if (task_no_new_privs(current) && !unconfined(label) &&
- !aa_label_is_unconfined_subset(new, ctx->nnp)) {
+ !aa_label_is_unconfined_subset(new, label)) {
/* not an apparmor denial per se, so don't log it */
AA_DEBUG("no_new_privs - change_hat denied");
error = -EPERM;
diff --git a/security/apparmor/include/task.h b/security/apparmor/include/task.h
index f13d12373b25..8a9c258e2018 100644
--- a/security/apparmor/include/task.h
+++ b/security/apparmor/include/task.h
@@ -17,13 +17,11 @@ static inline struct aa_task_ctx *task_ctx(struct task_struct *task)
/*
* struct aa_task_ctx - information for current task label change
- * @nnp: snapshot of label at time of no_new_privs
* @onexec: profile to transition to on next exec (MAY BE NULL)
* @previous: profile the task may return to (MAY BE NULL)
* @token: magic value the task must know for returning to @previous_profile
*/
struct aa_task_ctx {
- struct aa_label *nnp;
struct aa_label *onexec;
struct aa_label *previous;
u64 token;
@@ -42,7 +40,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task);
static inline void aa_free_task_ctx(struct aa_task_ctx *ctx)
{
if (ctx) {
- aa_put_label(ctx->nnp);
aa_put_label(ctx->previous);
aa_put_label(ctx->onexec);
}
@@ -57,7 +54,6 @@ static inline void aa_dup_task_ctx(struct aa_task_ctx *new,
const struct aa_task_ctx *old)
{
*new = *old;
- aa_get_label(new->nnp);
aa_get_label(new->previous);
aa_get_label(new->onexec);
}
diff --git a/security/apparmor/task.c b/security/apparmor/task.c
index d17130ee6795..4b9ec370a171 100644
--- a/security/apparmor/task.c
+++ b/security/apparmor/task.c
@@ -41,7 +41,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task)
int aa_replace_current_label(struct aa_label *label)
{
struct aa_label *old = aa_current_raw_label();
- struct aa_task_ctx *ctx = task_ctx(current);
struct cred *new;
AA_BUG(!label);
@@ -56,12 +55,6 @@ int aa_replace_current_label(struct aa_label *label)
if (!new)
return -ENOMEM;
- if (ctx->nnp && label_is_stale(ctx->nnp)) {
- struct aa_label *tmp = ctx->nnp;
-
- ctx->nnp = aa_get_newest_label(tmp);
- aa_put_label(tmp);
- }
if (unconfined(label) || (labels_ns(old) != labels_ns(label)))
/*
* if switching to unconfined or a different label namespace
--
2.20.1
Eric
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [RFC][PATCH] apparmor: Enforce progressively tighter permissions for no_new_privs
2021-01-20 21:26 [RFC][PATCH] apparmor: Enforce progressively tighter permissions for no_new_privs Eric W. Biederman
@ 2021-01-20 21:38 ` Eric W. Biederman
2021-01-20 22:32 ` John Johansen
1 sibling, 0 replies; 5+ messages in thread
From: Eric W. Biederman @ 2021-01-20 21:38 UTC (permalink / raw)
To: linux-security-module
Cc: Andy Lutomirski, Kees Cook, James Morris, John Johansen,
apparmor, linux-kernel, Linus Torvalds
This should now Cc the correct email address for James Morris.
ebiederm@xmission.com (Eric W. Biederman) writes:
> The current understanding of apparmor with respect to no_new_privs is at
> odds with how no_new_privs is implemented and understood by the rest of
> the kernel.
>
> The documentation of no_new_privs states:
>> With ``no_new_privs`` set, ``execve()`` promises not to grant the
>> privilege to do anything that could not have been done without the
>> execve call.
>
> And reading through the kernel except for apparmor that description
> matches what is implemented.
>
> There are two major divergences of apparmor from this definition:
> - proc_setattr enforces limitations when no_new_privs are set.
> - the limitation is enforced from the apparent time when no_new_privs is
> set instead of guaranteeing that each execve has progressively more
> narrow permissions.
>
> The code in apparmor that attempts to discover the apparmor label at the
> point where no_new_privs is set is not robust. The capture happens a
> long time after no_new_privs is set.
>
> Capturing the label at the point where no_new_privs is set is
> practically impossible to implement robustly. Today the rule is struct
> cred can only be changed by it's current task. Today
> SECCOMP_FILTER_FLAG_TSYNC sets no_new_privs from another thread. A
> robust implementation would require changing something fundamental in
> how creds are managed for SECCOMP_FILTER_FLAG_TSYNC to be able to
> capture the cred at the point it is set.
>
> Futhermore given the consistent documentation and how everything else
> implements no_new_privs, not having the permissions get progressively
> tighter is a footgun aimed at userspace. I fully expect it to break any
> security sensitive software that uses no_new_privs and was not
> deliberately designed and tested against apparmor.
>
> Avoid the questionable and hard to fix implementation and the
> potential to confuse userspace by having no_new_privs enforce
> progressinvely tighter permissions.
>
> Fixes: 9fcf78cca198 ("apparmor: update domain transitions that are subsets of confinement at nnp")
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> ---
>
> I came accross this while examining the places cred_guard_mutex is
> used and trying to find a way to make those code paths less insane.
>
> If it would be more pallatable I would not mind removing the
> task_no_new_privs test entirely from aa_change_hat and aa_change_profile
> as those are not part of exec, so arguably no_new_privs should not care
> about them at all.
>
> Can we please get rid of the huge semantic wart and pain in the implementation?
>
> security/apparmor/domain.c | 39 ++++----------------------------
> security/apparmor/include/task.h | 4 ----
> security/apparmor/task.c | 7 ------
> 3 files changed, 4 insertions(+), 46 deletions(-)
>
> diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
> index f919ebd042fd..8f77059bf890 100644
> --- a/security/apparmor/domain.c
> +++ b/security/apparmor/domain.c
> @@ -869,17 +869,6 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
>
> label = aa_get_newest_label(cred_label(bprm->cred));
>
> - /*
> - * Detect no new privs being set, and store the label it
> - * occurred under. Ideally this would happen when nnp
> - * is set but there isn't a good way to do that yet.
> - *
> - * Testing for unconfined must be done before the subset test
> - */
> - if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) && !unconfined(label) &&
> - !ctx->nnp)
> - ctx->nnp = aa_get_label(label);
> -
> /* buffer freed below, name is pointer into buffer */
> buffer = aa_get_buffer(false);
> if (!buffer) {
> @@ -915,7 +904,7 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
> */
> if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) &&
> !unconfined(label) &&
> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
> + !aa_label_is_unconfined_subset(new, label)) {
> error = -EPERM;
> info = "no new privs";
> goto audit;
> @@ -1158,16 +1147,6 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
> label = aa_get_newest_cred_label(cred);
> previous = aa_get_newest_label(ctx->previous);
>
> - /*
> - * Detect no new privs being set, and store the label it
> - * occurred under. Ideally this would happen when nnp
> - * is set but there isn't a good way to do that yet.
> - *
> - * Testing for unconfined must be done before the subset test
> - */
> - if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
> - ctx->nnp = aa_get_label(label);
> -
> if (unconfined(label)) {
> info = "unconfined can not change_hat";
> error = -EPERM;
> @@ -1193,7 +1172,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
> * reduce restrictions.
> */
> if (task_no_new_privs(current) && !unconfined(label) &&
> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
> + !aa_label_is_unconfined_subset(new, label)) {
> /* not an apparmor denial per se, so don't log it */
> AA_DEBUG("no_new_privs - change_hat denied");
> error = -EPERM;
> @@ -1214,7 +1193,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
> * reduce restrictions.
> */
> if (task_no_new_privs(current) && !unconfined(label) &&
> - !aa_label_is_unconfined_subset(previous, ctx->nnp)) {
> + !aa_label_is_unconfined_subset(previous, label)) {
> /* not an apparmor denial per se, so don't log it */
> AA_DEBUG("no_new_privs - change_hat denied");
> error = -EPERM;
> @@ -1303,16 +1282,6 @@ int aa_change_profile(const char *fqname, int flags)
>
> label = aa_get_current_label();
>
> - /*
> - * Detect no new privs being set, and store the label it
> - * occurred under. Ideally this would happen when nnp
> - * is set but there isn't a good way to do that yet.
> - *
> - * Testing for unconfined must be done before the subset test
> - */
> - if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
> - ctx->nnp = aa_get_label(label);
> -
> if (!fqname || !*fqname) {
> aa_put_label(label);
> AA_DEBUG("no profile name");
> @@ -1409,7 +1378,7 @@ int aa_change_profile(const char *fqname, int flags)
> * reduce restrictions.
> */
> if (task_no_new_privs(current) && !unconfined(label) &&
> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
> + !aa_label_is_unconfined_subset(new, label)) {
> /* not an apparmor denial per se, so don't log it */
> AA_DEBUG("no_new_privs - change_hat denied");
> error = -EPERM;
> diff --git a/security/apparmor/include/task.h b/security/apparmor/include/task.h
> index f13d12373b25..8a9c258e2018 100644
> --- a/security/apparmor/include/task.h
> +++ b/security/apparmor/include/task.h
> @@ -17,13 +17,11 @@ static inline struct aa_task_ctx *task_ctx(struct task_struct *task)
>
> /*
> * struct aa_task_ctx - information for current task label change
> - * @nnp: snapshot of label at time of no_new_privs
> * @onexec: profile to transition to on next exec (MAY BE NULL)
> * @previous: profile the task may return to (MAY BE NULL)
> * @token: magic value the task must know for returning to @previous_profile
> */
> struct aa_task_ctx {
> - struct aa_label *nnp;
> struct aa_label *onexec;
> struct aa_label *previous;
> u64 token;
> @@ -42,7 +40,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task);
> static inline void aa_free_task_ctx(struct aa_task_ctx *ctx)
> {
> if (ctx) {
> - aa_put_label(ctx->nnp);
> aa_put_label(ctx->previous);
> aa_put_label(ctx->onexec);
> }
> @@ -57,7 +54,6 @@ static inline void aa_dup_task_ctx(struct aa_task_ctx *new,
> const struct aa_task_ctx *old)
> {
> *new = *old;
> - aa_get_label(new->nnp);
> aa_get_label(new->previous);
> aa_get_label(new->onexec);
> }
> diff --git a/security/apparmor/task.c b/security/apparmor/task.c
> index d17130ee6795..4b9ec370a171 100644
> --- a/security/apparmor/task.c
> +++ b/security/apparmor/task.c
> @@ -41,7 +41,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task)
> int aa_replace_current_label(struct aa_label *label)
> {
> struct aa_label *old = aa_current_raw_label();
> - struct aa_task_ctx *ctx = task_ctx(current);
> struct cred *new;
>
> AA_BUG(!label);
> @@ -56,12 +55,6 @@ int aa_replace_current_label(struct aa_label *label)
> if (!new)
> return -ENOMEM;
>
> - if (ctx->nnp && label_is_stale(ctx->nnp)) {
> - struct aa_label *tmp = ctx->nnp;
> -
> - ctx->nnp = aa_get_newest_label(tmp);
> - aa_put_label(tmp);
> - }
> if (unconfined(label) || (labels_ns(old) != labels_ns(label)))
> /*
> * if switching to unconfined or a different label namespace
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [RFC][PATCH] apparmor: Enforce progressively tighter permissions for no_new_privs
2021-01-20 21:26 [RFC][PATCH] apparmor: Enforce progressively tighter permissions for no_new_privs Eric W. Biederman
2021-01-20 21:38 ` Eric W. Biederman
@ 2021-01-20 22:32 ` John Johansen
2021-01-20 22:56 ` Eric W. Biederman
1 sibling, 1 reply; 5+ messages in thread
From: John Johansen @ 2021-01-20 22:32 UTC (permalink / raw)
To: Eric W. Biederman, linux-security-module
Cc: Andy Lutomirski, Kees Cook, James Morris, apparmor, linux-kernel,
Linus Torvalds, James Morris
On 1/20/21 1:26 PM, Eric W. Biederman wrote:
>
> The current understanding of apparmor with respect to no_new_privs is at
> odds with how no_new_privs is implemented and understood by the rest of
> the kernel.
>
> The documentation of no_new_privs states:
>> With ``no_new_privs`` set, ``execve()`` promises not to grant the
>> privilege to do anything that could not have been done without the
>> execve call.
>
> And reading through the kernel except for apparmor that description
> matches what is implemented.
>
That is not correct.
commit 7b0d0b40cd78 ("selinux: Permit bounded transitions under
NO_NEW_PRIVS or NOSUID.")
Allows for bound transitions under selinux
and
commit af63f4193f9f selinux: Generalize support for NNP/nosuid SELinux
domain transitions
goes further and "Decouple NNP/nosuid from SELinux transitions".
> There are two major divergences of apparmor from this definition:
> - proc_setattr enforces limitations when no_new_privs are set.
> - the limitation is enforced from the apparent time when no_new_privs is
> set instead of guaranteeing that each execve has progressively more
> narrow permissions.
>
> The code in apparmor that attempts to discover the apparmor label at the
> point where no_new_privs is set is not robust. The capture happens a
> long time after no_new_privs is set.
>
yes, but that shouldn't matter. As apparmor has not changed its label
at any point between when no_new_privs was set and when the check is
done. AppArmor is attempting to change it label, and if it finds NNP
has been set we capture what the confinement was.
> Capturing the label at the point where no_new_privs is set is
> practically impossible to implement robustly. Today the rule is struct
> cred can only be changed by it's current task. Today
right, and apparmor only ever has the task update its own label.
> SECCOMP_FILTER_FLAG_TSYNC sets no_new_privs from another thread. A
> robust implementation would require changing something fundamental in
> how creds are managed for SECCOMP_FILTER_FLAG_TSYNC to be able to
> capture the cred at the point it is set.
>
I am open to supporting something like that.
> Futhermore given the consistent documentation and how everything else
> implements no_new_privs, not having the permissions get progressively
Again see above
> tighter is a footgun aimed at userspace. I fully expect it to break any
tighter is somewhat relative, nor is it only progressively tighter it
is bounded against the snapshot of the label that was on the task.
> security sensitive software that uses no_new_privs and was not
> deliberately designed and tested against apparmor.
>
Currently the situation has become either an either or choice between
the LSM and NNP. We are trying to walk a balance. Ideally apparmor
would like to do something similar to selinux and decouple the label
transition from NNP and nosuid via an internal capability, but we
have not gone there yet.
> Avoid the questionable and hard to fix implementation and the
> potential to confuse userspace by having no_new_privs enforce
> progressinvely tighter permissions.
>
This would completely break several use cases.
> Fixes: 9fcf78cca198 ("apparmor: update domain transitions that are subsets of confinement at nnp")
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> ---
>
> I came accross this while examining the places cred_guard_mutex is
> used and trying to find a way to make those code paths less insane.
>
> If it would be more pallatable I would not mind removing the
> task_no_new_privs test entirely from aa_change_hat and aa_change_profile
> as those are not part of exec, so arguably no_new_privs should not care
> about them at all.
>
> Can we please get rid of the huge semantic wart and pain in the implementation?
>
> security/apparmor/domain.c | 39 ++++----------------------------
> security/apparmor/include/task.h | 4 ----
> security/apparmor/task.c | 7 ------
> 3 files changed, 4 insertions(+), 46 deletions(-)
>
> diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
> index f919ebd042fd..8f77059bf890 100644
> --- a/security/apparmor/domain.c
> +++ b/security/apparmor/domain.c
> @@ -869,17 +869,6 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
>
> label = aa_get_newest_label(cred_label(bprm->cred));
>
> - /*
> - * Detect no new privs being set, and store the label it
> - * occurred under. Ideally this would happen when nnp
> - * is set but there isn't a good way to do that yet.
> - *
> - * Testing for unconfined must be done before the subset test
> - */
> - if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) && !unconfined(label) &&
> - !ctx->nnp)
> - ctx->nnp = aa_get_label(label);
> -
> /* buffer freed below, name is pointer into buffer */
> buffer = aa_get_buffer(false);
> if (!buffer) {
> @@ -915,7 +904,7 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
> */
> if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) &&
> !unconfined(label) &&
> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
> + !aa_label_is_unconfined_subset(new, label)) {
> error = -EPERM;
> info = "no new privs";
> goto audit;
> @@ -1158,16 +1147,6 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
> label = aa_get_newest_cred_label(cred);
> previous = aa_get_newest_label(ctx->previous);
>
> - /*
> - * Detect no new privs being set, and store the label it
> - * occurred under. Ideally this would happen when nnp
> - * is set but there isn't a good way to do that yet.
> - *
> - * Testing for unconfined must be done before the subset test
> - */
> - if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
> - ctx->nnp = aa_get_label(label);
> -
> if (unconfined(label)) {
> info = "unconfined can not change_hat";
> error = -EPERM;
> @@ -1193,7 +1172,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
> * reduce restrictions.
> */
> if (task_no_new_privs(current) && !unconfined(label) &&
> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
> + !aa_label_is_unconfined_subset(new, label)) {
> /* not an apparmor denial per se, so don't log it */
> AA_DEBUG("no_new_privs - change_hat denied");
> error = -EPERM;
> @@ -1214,7 +1193,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
> * reduce restrictions.
> */
> if (task_no_new_privs(current) && !unconfined(label) &&
> - !aa_label_is_unconfined_subset(previous, ctx->nnp)) {
> + !aa_label_is_unconfined_subset(previous, label)) {
> /* not an apparmor denial per se, so don't log it */
> AA_DEBUG("no_new_privs - change_hat denied");
> error = -EPERM;
> @@ -1303,16 +1282,6 @@ int aa_change_profile(const char *fqname, int flags)
>
> label = aa_get_current_label();
>
> - /*
> - * Detect no new privs being set, and store the label it
> - * occurred under. Ideally this would happen when nnp
> - * is set but there isn't a good way to do that yet.
> - *
> - * Testing for unconfined must be done before the subset test
> - */
> - if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
> - ctx->nnp = aa_get_label(label);
> -
> if (!fqname || !*fqname) {
> aa_put_label(label);
> AA_DEBUG("no profile name");
> @@ -1409,7 +1378,7 @@ int aa_change_profile(const char *fqname, int flags)
> * reduce restrictions.
> */
> if (task_no_new_privs(current) && !unconfined(label) &&
> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
> + !aa_label_is_unconfined_subset(new, label)) {
> /* not an apparmor denial per se, so don't log it */
> AA_DEBUG("no_new_privs - change_hat denied");
> error = -EPERM;
> diff --git a/security/apparmor/include/task.h b/security/apparmor/include/task.h
> index f13d12373b25..8a9c258e2018 100644
> --- a/security/apparmor/include/task.h
> +++ b/security/apparmor/include/task.h
> @@ -17,13 +17,11 @@ static inline struct aa_task_ctx *task_ctx(struct task_struct *task)
>
> /*
> * struct aa_task_ctx - information for current task label change
> - * @nnp: snapshot of label at time of no_new_privs
> * @onexec: profile to transition to on next exec (MAY BE NULL)
> * @previous: profile the task may return to (MAY BE NULL)
> * @token: magic value the task must know for returning to @previous_profile
> */
> struct aa_task_ctx {
> - struct aa_label *nnp;
> struct aa_label *onexec;
> struct aa_label *previous;
> u64 token;
> @@ -42,7 +40,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task);
> static inline void aa_free_task_ctx(struct aa_task_ctx *ctx)
> {
> if (ctx) {
> - aa_put_label(ctx->nnp);
> aa_put_label(ctx->previous);
> aa_put_label(ctx->onexec);
> }
> @@ -57,7 +54,6 @@ static inline void aa_dup_task_ctx(struct aa_task_ctx *new,
> const struct aa_task_ctx *old)
> {
> *new = *old;
> - aa_get_label(new->nnp);
> aa_get_label(new->previous);
> aa_get_label(new->onexec);
> }
> diff --git a/security/apparmor/task.c b/security/apparmor/task.c
> index d17130ee6795..4b9ec370a171 100644
> --- a/security/apparmor/task.c
> +++ b/security/apparmor/task.c
> @@ -41,7 +41,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task)
> int aa_replace_current_label(struct aa_label *label)
> {
> struct aa_label *old = aa_current_raw_label();
> - struct aa_task_ctx *ctx = task_ctx(current);
> struct cred *new;
>
> AA_BUG(!label);
> @@ -56,12 +55,6 @@ int aa_replace_current_label(struct aa_label *label)
> if (!new)
> return -ENOMEM;
>
> - if (ctx->nnp && label_is_stale(ctx->nnp)) {
> - struct aa_label *tmp = ctx->nnp;
> -
> - ctx->nnp = aa_get_newest_label(tmp);
> - aa_put_label(tmp);
> - }
> if (unconfined(label) || (labels_ns(old) != labels_ns(label)))
> /*
> * if switching to unconfined or a different label namespace
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [RFC][PATCH] apparmor: Enforce progressively tighter permissions for no_new_privs
2021-01-20 22:32 ` John Johansen
@ 2021-01-20 22:56 ` Eric W. Biederman
2021-01-20 23:05 ` John Johansen
0 siblings, 1 reply; 5+ messages in thread
From: Eric W. Biederman @ 2021-01-20 22:56 UTC (permalink / raw)
To: John Johansen
Cc: linux-security-module, Andy Lutomirski, Kees Cook, James Morris,
apparmor, linux-kernel, Linus Torvalds, James Morris
TL;DR ????selinux and apparmor ignore no_new_privs????
What?????
John Johansen <john.johansen@canonical.com> writes:
> On 1/20/21 1:26 PM, Eric W. Biederman wrote:
>>
>> The current understanding of apparmor with respect to no_new_privs is at
>> odds with how no_new_privs is implemented and understood by the rest of
>> the kernel.
>>
>> The documentation of no_new_privs states:
>>> With ``no_new_privs`` set, ``execve()`` promises not to grant the
>>> privilege to do anything that could not have been done without the
>>> execve call.
>>
>> And reading through the kernel except for apparmor that description
>> matches what is implemented.
>>
>
> That is not correct.
>
> commit 7b0d0b40cd78 ("selinux: Permit bounded transitions under
> NO_NEW_PRIVS or NOSUID.")
>
> Allows for bound transitions under selinux
> and
As I understand a bound transition it is a transition to a state with
a set of permissions that are a subset of what was previously held.
Which is consistent with the mandate of no_new_privs.
> commit af63f4193f9f selinux: Generalize support for NNP/nosuid SELinux
> domain transitions
>
> goes further and "Decouple NNP/nosuid from SELinux transitions".
Yes. Looking at that commit I do see that selinux appears to be
deliberately ignoring no_new_privs in specific cases.
WTF.
>> There are two major divergences of apparmor from this definition:
>> - proc_setattr enforces limitations when no_new_privs are set.
>> - the limitation is enforced from the apparent time when no_new_privs is
>> set instead of guaranteeing that each execve has progressively more
>> narrow permissions.
>>
>> The code in apparmor that attempts to discover the apparmor label at the
>> point where no_new_privs is set is not robust. The capture happens a
>> long time after no_new_privs is set.
>>
>
> yes, but that shouldn't matter. As apparmor has not changed its label
> at any point between when no_new_privs was set and when the check is
> done. AppArmor is attempting to change it label, and if it finds NNP
> has been set we capture what the confinement was.
>
>> Capturing the label at the point where no_new_privs is set is
>> practically impossible to implement robustly. Today the rule is struct
>> cred can only be changed by it's current task. Today
>
> right, and apparmor only ever has the task update its own label.
>
>> SECCOMP_FILTER_FLAG_TSYNC sets no_new_privs from another thread. A
>> robust implementation would require changing something fundamental in
>> how creds are managed for SECCOMP_FILTER_FLAG_TSYNC to be able to
>> capture the cred at the point it is set.
>>
> I am open to supporting something like that.
I can't see how it would be possible to be robust without completely
changing the locking. Locking that right now in a simpler model we have
not figured out how to make obviously correct.
>> Futhermore given the consistent documentation and how everything else
>> implements no_new_privs, not having the permissions get progressively
>
> Again see above
Except where selinux deliberately ignores no_new_privs this is
consitent.
>> tighter is a footgun aimed at userspace. I fully expect it to break any
>
> tighter is somewhat relative, nor is it only progressively tighter it
> is bounded against the snapshot of the label that was on the task.
Which is the BUG I am reporting. It should be progressingly tighter.
>> security sensitive software that uses no_new_privs and was not
>> deliberately designed and tested against apparmor.
>>
>
> Currently the situation has become either an either or choice between
> the LSM and NNP. We are trying to walk a balance. Ideally apparmor
> would like to do something similar to selinux and decouple the label
> transition from NNP and nosuid via an internal capability, but we
> have not gone there yet.
Why do you need to escape no_new_privs. Why does anyone need to escape
no_new_privs?
>> Avoid the questionable and hard to fix implementation and the
>> potential to confuse userspace by having no_new_privs enforce
>> progressinvely tighter permissions.
>>
>
> This would completely break several use cases.
Enforcing no_new_privs as documented would break userspace?
Isn't the opposite true that you are breaking people by not enforcing
it?
>> Fixes: 9fcf78cca198 ("apparmor: update domain transitions that are subsets of confinement at nnp")
>> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
>> ---
>>
>> I came accross this while examining the places cred_guard_mutex is
>> used and trying to find a way to make those code paths less insane.
>>
>> If it would be more pallatable I would not mind removing the
>> task_no_new_privs test entirely from aa_change_hat and aa_change_profile
>> as those are not part of exec, so arguably no_new_privs should not care
>> about them at all.
>>
>> Can we please get rid of the huge semantic wart and pain in the implementation?
>>
>> security/apparmor/domain.c | 39 ++++----------------------------
>> security/apparmor/include/task.h | 4 ----
>> security/apparmor/task.c | 7 ------
>> 3 files changed, 4 insertions(+), 46 deletions(-)
>>
>> diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
>> index f919ebd042fd..8f77059bf890 100644
>> --- a/security/apparmor/domain.c
>> +++ b/security/apparmor/domain.c
>> @@ -869,17 +869,6 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
>>
>> label = aa_get_newest_label(cred_label(bprm->cred));
>>
>> - /*
>> - * Detect no new privs being set, and store the label it
>> - * occurred under. Ideally this would happen when nnp
>> - * is set but there isn't a good way to do that yet.
>> - *
>> - * Testing for unconfined must be done before the subset test
>> - */
>> - if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) && !unconfined(label) &&
>> - !ctx->nnp)
>> - ctx->nnp = aa_get_label(label);
>> -
>> /* buffer freed below, name is pointer into buffer */
>> buffer = aa_get_buffer(false);
>> if (!buffer) {
>> @@ -915,7 +904,7 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
>> */
>> if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) &&
>> !unconfined(label) &&
>> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
>> + !aa_label_is_unconfined_subset(new, label)) {
>> error = -EPERM;
>> info = "no new privs";
>> goto audit;
>> @@ -1158,16 +1147,6 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
>> label = aa_get_newest_cred_label(cred);
>> previous = aa_get_newest_label(ctx->previous);
>>
>> - /*
>> - * Detect no new privs being set, and store the label it
>> - * occurred under. Ideally this would happen when nnp
>> - * is set but there isn't a good way to do that yet.
>> - *
>> - * Testing for unconfined must be done before the subset test
>> - */
>> - if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
>> - ctx->nnp = aa_get_label(label);
>> -
>> if (unconfined(label)) {
>> info = "unconfined can not change_hat";
>> error = -EPERM;
>> @@ -1193,7 +1172,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
>> * reduce restrictions.
>> */
>> if (task_no_new_privs(current) && !unconfined(label) &&
>> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
>> + !aa_label_is_unconfined_subset(new, label)) {
>> /* not an apparmor denial per se, so don't log it */
>> AA_DEBUG("no_new_privs - change_hat denied");
>> error = -EPERM;
>> @@ -1214,7 +1193,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
>> * reduce restrictions.
>> */
>> if (task_no_new_privs(current) && !unconfined(label) &&
>> - !aa_label_is_unconfined_subset(previous, ctx->nnp)) {
>> + !aa_label_is_unconfined_subset(previous, label)) {
>> /* not an apparmor denial per se, so don't log it */
>> AA_DEBUG("no_new_privs - change_hat denied");
>> error = -EPERM;
>> @@ -1303,16 +1282,6 @@ int aa_change_profile(const char *fqname, int flags)
>>
>> label = aa_get_current_label();
>>
>> - /*
>> - * Detect no new privs being set, and store the label it
>> - * occurred under. Ideally this would happen when nnp
>> - * is set but there isn't a good way to do that yet.
>> - *
>> - * Testing for unconfined must be done before the subset test
>> - */
>> - if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
>> - ctx->nnp = aa_get_label(label);
>> -
>> if (!fqname || !*fqname) {
>> aa_put_label(label);
>> AA_DEBUG("no profile name");
>> @@ -1409,7 +1378,7 @@ int aa_change_profile(const char *fqname, int flags)
>> * reduce restrictions.
>> */
>> if (task_no_new_privs(current) && !unconfined(label) &&
>> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
>> + !aa_label_is_unconfined_subset(new, label)) {
>> /* not an apparmor denial per se, so don't log it */
>> AA_DEBUG("no_new_privs - change_hat denied");
>> error = -EPERM;
>> diff --git a/security/apparmor/include/task.h b/security/apparmor/include/task.h
>> index f13d12373b25..8a9c258e2018 100644
>> --- a/security/apparmor/include/task.h
>> +++ b/security/apparmor/include/task.h
>> @@ -17,13 +17,11 @@ static inline struct aa_task_ctx *task_ctx(struct task_struct *task)
>>
>> /*
>> * struct aa_task_ctx - information for current task label change
>> - * @nnp: snapshot of label at time of no_new_privs
>> * @onexec: profile to transition to on next exec (MAY BE NULL)
>> * @previous: profile the task may return to (MAY BE NULL)
>> * @token: magic value the task must know for returning to @previous_profile
>> */
>> struct aa_task_ctx {
>> - struct aa_label *nnp;
>> struct aa_label *onexec;
>> struct aa_label *previous;
>> u64 token;
>> @@ -42,7 +40,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task);
>> static inline void aa_free_task_ctx(struct aa_task_ctx *ctx)
>> {
>> if (ctx) {
>> - aa_put_label(ctx->nnp);
>> aa_put_label(ctx->previous);
>> aa_put_label(ctx->onexec);
>> }
>> @@ -57,7 +54,6 @@ static inline void aa_dup_task_ctx(struct aa_task_ctx *new,
>> const struct aa_task_ctx *old)
>> {
>> *new = *old;
>> - aa_get_label(new->nnp);
>> aa_get_label(new->previous);
>> aa_get_label(new->onexec);
>> }
>> diff --git a/security/apparmor/task.c b/security/apparmor/task.c
>> index d17130ee6795..4b9ec370a171 100644
>> --- a/security/apparmor/task.c
>> +++ b/security/apparmor/task.c
>> @@ -41,7 +41,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task)
>> int aa_replace_current_label(struct aa_label *label)
>> {
>> struct aa_label *old = aa_current_raw_label();
>> - struct aa_task_ctx *ctx = task_ctx(current);
>> struct cred *new;
>>
>> AA_BUG(!label);
>> @@ -56,12 +55,6 @@ int aa_replace_current_label(struct aa_label *label)
>> if (!new)
>> return -ENOMEM;
>>
>> - if (ctx->nnp && label_is_stale(ctx->nnp)) {
>> - struct aa_label *tmp = ctx->nnp;
>> -
>> - ctx->nnp = aa_get_newest_label(tmp);
>> - aa_put_label(tmp);
>> - }
>> if (unconfined(label) || (labels_ns(old) != labels_ns(label)))
>> /*
>> * if switching to unconfined or a different label namespace
>>
Eric
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [RFC][PATCH] apparmor: Enforce progressively tighter permissions for no_new_privs
2021-01-20 22:56 ` Eric W. Biederman
@ 2021-01-20 23:05 ` John Johansen
0 siblings, 0 replies; 5+ messages in thread
From: John Johansen @ 2021-01-20 23:05 UTC (permalink / raw)
To: Eric W. Biederman
Cc: linux-security-module, Andy Lutomirski, Kees Cook, James Morris,
apparmor, linux-kernel, Linus Torvalds, James Morris
On 1/20/21 2:56 PM, Eric W. Biederman wrote:
>
> TL;DR ????selinux and apparmor ignore no_new_privs????
>
> What?????
>
AppArmor does not ignore no_new_privs. Its mediation is bounded
and it doesn't grant anything that wasn't allowed when NNP was
set.
>
> John Johansen <john.johansen@canonical.com> writes:
>
>> On 1/20/21 1:26 PM, Eric W. Biederman wrote:
>>>
>>> The current understanding of apparmor with respect to no_new_privs is at
>>> odds with how no_new_privs is implemented and understood by the rest of
>>> the kernel.
>>>
>>> The documentation of no_new_privs states:
>>>> With ``no_new_privs`` set, ``execve()`` promises not to grant the
>>>> privilege to do anything that could not have been done without the
>>>> execve call.
>>>
>>> And reading through the kernel except for apparmor that description
>>> matches what is implemented.
>>>
>>
>> That is not correct.
>>
>> commit 7b0d0b40cd78 ("selinux: Permit bounded transitions under
>> NO_NEW_PRIVS or NOSUID.")
>>
>> Allows for bound transitions under selinux
>> and
>
> As I understand a bound transition it is a transition to a state with
> a set of permissions that are a subset of what was previously held.
> Which is consistent with the mandate of no_new_privs.
>
>> commit af63f4193f9f selinux: Generalize support for NNP/nosuid SELinux
>> domain transitions
>>
>> goes further and "Decouple NNP/nosuid from SELinux transitions".
>
> Yes. Looking at that commit I do see that selinux appears to be
> deliberately ignoring no_new_privs in specific cases.
>
> WTF.
>
>>> There are two major divergences of apparmor from this definition:
>>> - proc_setattr enforces limitations when no_new_privs are set.
>>> - the limitation is enforced from the apparent time when no_new_privs is
>>> set instead of guaranteeing that each execve has progressively more
>>> narrow permissions.
>>>
>>> The code in apparmor that attempts to discover the apparmor label at the
>>> point where no_new_privs is set is not robust. The capture happens a
>>> long time after no_new_privs is set.
>>>
>>
>> yes, but that shouldn't matter. As apparmor has not changed its label
>> at any point between when no_new_privs was set and when the check is
>> done. AppArmor is attempting to change it label, and if it finds NNP
>> has been set we capture what the confinement was.
>>
>>> Capturing the label at the point where no_new_privs is set is
>>> practically impossible to implement robustly. Today the rule is struct
>>> cred can only be changed by it's current task. Today
>>
>> right, and apparmor only ever has the task update its own label.
>>
>>> SECCOMP_FILTER_FLAG_TSYNC sets no_new_privs from another thread. A
>>> robust implementation would require changing something fundamental in
>>> how creds are managed for SECCOMP_FILTER_FLAG_TSYNC to be able to
>>> capture the cred at the point it is set.
>>>
>> I am open to supporting something like that.
>
> I can't see how it would be possible to be robust without completely
> changing the locking. Locking that right now in a simpler model we have
> not figured out how to make obviously correct.
>
>>> Futhermore given the consistent documentation and how everything else
>>> implements no_new_privs, not having the permissions get progressively
>>
>> Again see above
>
> Except where selinux deliberately ignores no_new_privs this is
> consitent.
>
>>> tighter is a footgun aimed at userspace. I fully expect it to break any
>>
>> tighter is somewhat relative, nor is it only progressively tighter it
>> is bounded against the snapshot of the label that was on the task.
>
> Which is the BUG I am reporting. It should be progressingly tighter.
>
>>> security sensitive software that uses no_new_privs and was not
>>> deliberately designed and tested against apparmor.
>>>
>>
>> Currently the situation has become either an either or choice between
>> the LSM and NNP. We are trying to walk a balance. Ideally apparmor
>> would like to do something similar to selinux and decouple the label
>> transition from NNP and nosuid via an internal capability, but we
>> have not gone there yet.
>
> Why do you need to escape no_new_privs. Why does anyone need to escape
> no_new_privs?
>
>>> Avoid the questionable and hard to fix implementation and the
>>> potential to confuse userspace by having no_new_privs enforce
>>> progressinvely tighter permissions.
>>>
>>
>> This would completely break several use cases.
>
> Enforcing no_new_privs as documented would break userspace?
>
> Isn't the opposite true that you are breaking people by not enforcing
> it?
>
>>> Fixes: 9fcf78cca198 ("apparmor: update domain transitions that are subsets of confinement at nnp")
>>> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
>>> ---
>>>
>>> I came accross this while examining the places cred_guard_mutex is
>>> used and trying to find a way to make those code paths less insane.
>>>
>>> If it would be more pallatable I would not mind removing the
>>> task_no_new_privs test entirely from aa_change_hat and aa_change_profile
>>> as those are not part of exec, so arguably no_new_privs should not care
>>> about them at all.
>>>
>>> Can we please get rid of the huge semantic wart and pain in the implementation?
>>>
>>> security/apparmor/domain.c | 39 ++++----------------------------
>>> security/apparmor/include/task.h | 4 ----
>>> security/apparmor/task.c | 7 ------
>>> 3 files changed, 4 insertions(+), 46 deletions(-)
>>>
>>> diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
>>> index f919ebd042fd..8f77059bf890 100644
>>> --- a/security/apparmor/domain.c
>>> +++ b/security/apparmor/domain.c
>>> @@ -869,17 +869,6 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
>>>
>>> label = aa_get_newest_label(cred_label(bprm->cred));
>>>
>>> - /*
>>> - * Detect no new privs being set, and store the label it
>>> - * occurred under. Ideally this would happen when nnp
>>> - * is set but there isn't a good way to do that yet.
>>> - *
>>> - * Testing for unconfined must be done before the subset test
>>> - */
>>> - if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) && !unconfined(label) &&
>>> - !ctx->nnp)
>>> - ctx->nnp = aa_get_label(label);
>>> -
>>> /* buffer freed below, name is pointer into buffer */
>>> buffer = aa_get_buffer(false);
>>> if (!buffer) {
>>> @@ -915,7 +904,7 @@ int apparmor_bprm_creds_for_exec(struct linux_binprm *bprm)
>>> */
>>> if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) &&
>>> !unconfined(label) &&
>>> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
>>> + !aa_label_is_unconfined_subset(new, label)) {
>>> error = -EPERM;
>>> info = "no new privs";
>>> goto audit;
>>> @@ -1158,16 +1147,6 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
>>> label = aa_get_newest_cred_label(cred);
>>> previous = aa_get_newest_label(ctx->previous);
>>>
>>> - /*
>>> - * Detect no new privs being set, and store the label it
>>> - * occurred under. Ideally this would happen when nnp
>>> - * is set but there isn't a good way to do that yet.
>>> - *
>>> - * Testing for unconfined must be done before the subset test
>>> - */
>>> - if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
>>> - ctx->nnp = aa_get_label(label);
>>> -
>>> if (unconfined(label)) {
>>> info = "unconfined can not change_hat";
>>> error = -EPERM;
>>> @@ -1193,7 +1172,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
>>> * reduce restrictions.
>>> */
>>> if (task_no_new_privs(current) && !unconfined(label) &&
>>> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
>>> + !aa_label_is_unconfined_subset(new, label)) {
>>> /* not an apparmor denial per se, so don't log it */
>>> AA_DEBUG("no_new_privs - change_hat denied");
>>> error = -EPERM;
>>> @@ -1214,7 +1193,7 @@ int aa_change_hat(const char *hats[], int count, u64 token, int flags)
>>> * reduce restrictions.
>>> */
>>> if (task_no_new_privs(current) && !unconfined(label) &&
>>> - !aa_label_is_unconfined_subset(previous, ctx->nnp)) {
>>> + !aa_label_is_unconfined_subset(previous, label)) {
>>> /* not an apparmor denial per se, so don't log it */
>>> AA_DEBUG("no_new_privs - change_hat denied");
>>> error = -EPERM;
>>> @@ -1303,16 +1282,6 @@ int aa_change_profile(const char *fqname, int flags)
>>>
>>> label = aa_get_current_label();
>>>
>>> - /*
>>> - * Detect no new privs being set, and store the label it
>>> - * occurred under. Ideally this would happen when nnp
>>> - * is set but there isn't a good way to do that yet.
>>> - *
>>> - * Testing for unconfined must be done before the subset test
>>> - */
>>> - if (task_no_new_privs(current) && !unconfined(label) && !ctx->nnp)
>>> - ctx->nnp = aa_get_label(label);
>>> -
>>> if (!fqname || !*fqname) {
>>> aa_put_label(label);
>>> AA_DEBUG("no profile name");
>>> @@ -1409,7 +1378,7 @@ int aa_change_profile(const char *fqname, int flags)
>>> * reduce restrictions.
>>> */
>>> if (task_no_new_privs(current) && !unconfined(label) &&
>>> - !aa_label_is_unconfined_subset(new, ctx->nnp)) {
>>> + !aa_label_is_unconfined_subset(new, label)) {
>>> /* not an apparmor denial per se, so don't log it */
>>> AA_DEBUG("no_new_privs - change_hat denied");
>>> error = -EPERM;
>>> diff --git a/security/apparmor/include/task.h b/security/apparmor/include/task.h
>>> index f13d12373b25..8a9c258e2018 100644
>>> --- a/security/apparmor/include/task.h
>>> +++ b/security/apparmor/include/task.h
>>> @@ -17,13 +17,11 @@ static inline struct aa_task_ctx *task_ctx(struct task_struct *task)
>>>
>>> /*
>>> * struct aa_task_ctx - information for current task label change
>>> - * @nnp: snapshot of label at time of no_new_privs
>>> * @onexec: profile to transition to on next exec (MAY BE NULL)
>>> * @previous: profile the task may return to (MAY BE NULL)
>>> * @token: magic value the task must know for returning to @previous_profile
>>> */
>>> struct aa_task_ctx {
>>> - struct aa_label *nnp;
>>> struct aa_label *onexec;
>>> struct aa_label *previous;
>>> u64 token;
>>> @@ -42,7 +40,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task);
>>> static inline void aa_free_task_ctx(struct aa_task_ctx *ctx)
>>> {
>>> if (ctx) {
>>> - aa_put_label(ctx->nnp);
>>> aa_put_label(ctx->previous);
>>> aa_put_label(ctx->onexec);
>>> }
>>> @@ -57,7 +54,6 @@ static inline void aa_dup_task_ctx(struct aa_task_ctx *new,
>>> const struct aa_task_ctx *old)
>>> {
>>> *new = *old;
>>> - aa_get_label(new->nnp);
>>> aa_get_label(new->previous);
>>> aa_get_label(new->onexec);
>>> }
>>> diff --git a/security/apparmor/task.c b/security/apparmor/task.c
>>> index d17130ee6795..4b9ec370a171 100644
>>> --- a/security/apparmor/task.c
>>> +++ b/security/apparmor/task.c
>>> @@ -41,7 +41,6 @@ struct aa_label *aa_get_task_label(struct task_struct *task)
>>> int aa_replace_current_label(struct aa_label *label)
>>> {
>>> struct aa_label *old = aa_current_raw_label();
>>> - struct aa_task_ctx *ctx = task_ctx(current);
>>> struct cred *new;
>>>
>>> AA_BUG(!label);
>>> @@ -56,12 +55,6 @@ int aa_replace_current_label(struct aa_label *label)
>>> if (!new)
>>> return -ENOMEM;
>>>
>>> - if (ctx->nnp && label_is_stale(ctx->nnp)) {
>>> - struct aa_label *tmp = ctx->nnp;
>>> -
>>> - ctx->nnp = aa_get_newest_label(tmp);
>>> - aa_put_label(tmp);
>>> - }
>>> if (unconfined(label) || (labels_ns(old) != labels_ns(label)))
>>> /*
>>> * if switching to unconfined or a different label namespace
>>>
>
> Eric
>
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-01-21 3:02 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-01-20 21:26 [RFC][PATCH] apparmor: Enforce progressively tighter permissions for no_new_privs Eric W. Biederman
2021-01-20 21:38 ` Eric W. Biederman
2021-01-20 22:32 ` John Johansen
2021-01-20 22:56 ` Eric W. Biederman
2021-01-20 23:05 ` John Johansen
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