Commit 02a52c5c8c3b ("selinux: move policy commit after updating
selinuxfs") moved the selinux_policy_commit() call out of
security_load_policy() into sel_write_load(), which caused a subtle yet
rather serious bug.
The problem is that security_load_policy() passes a reference to the
convert_params local variable to sidtab_convert(), which stores it in
the sidtab, where it may be accessed until the policy is swapped over
and RCU synchronized. Before 02a52c5c8c3b, selinux_policy_commit() was
called directly from security_load_policy(), so the convert_params
pointer remained valid all the way until the old sidtab was destroyed,
but now that's no longer the case and calls to sidtab_context_to_sid()
on the old sidtab after security_load_policy() returns may cause invalid
memory accesses.
This can be easily triggered using the stress test from commit
ee1a84fdfeed ("selinux: overhaul sidtab to fix bug and improve
performance"):
```
function rand_cat() {
echo $(( $RANDOM % 1024 ))
}
function do_work() {
while true; do
echo -n "system_u:system_r:kernel_t:s0:c$(rand_cat),c$(rand_cat)" \
>/sys/fs/selinux/context 2>/dev/null || true
done
}
do_work >/dev/null &
do_work >/dev/null &
do_work >/dev/null &
while load_policy; do echo -n .; sleep 0.1; done
kill %1
kill %2
kill %3
```
Fix this by allocating the temporary sidtab convert structures
dynamically and passing them among the
selinux_policy_{load,cancel,commit} functions.
Note that this commit also fixes the minor issue of logging a
MAC_POLICY_LOAD audit record in case sel_make_policy_nodes() fails (in
which case the new policy isn't actually loaded).
Fixes: 02a52c5c8c3b ("selinux: move policy commit after updating selinuxfs")
Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
---
security/selinux/include/security.h | 15 ++++++---
security/selinux/selinuxfs.c | 10 +++---
security/selinux/ss/services.c | 51 +++++++++++++++++++----------
3 files changed, 49 insertions(+), 27 deletions(-)
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index 765a258a899e..25db66e0ac51 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -219,14 +219,21 @@ static inline bool selinux_policycap_genfs_seclabel_symlinks(void)
return READ_ONCE(state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS]);
}
+struct selinux_policy_convert_data;
+
+struct selinux_load_state {
+ struct selinux_policy *policy;
+ struct selinux_policy_convert_data *convert_data;
+};
+
int security_mls_enabled(struct selinux_state *state);
int security_load_policy(struct selinux_state *state,
- void *data, size_t len,
- struct selinux_policy **newpolicyp);
+ void *data, size_t len,
+ struct selinux_load_state *load_state);
void selinux_policy_commit(struct selinux_state *state,
- struct selinux_policy *newpolicy);
+ struct selinux_load_state *load_state);
void selinux_policy_cancel(struct selinux_state *state,
- struct selinux_policy *policy);
+ struct selinux_load_state *load_state);
int security_read_policy(struct selinux_state *state,
void **data, size_t *len);
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 340711e3dc9a..158d44ea93f4 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -616,7 +616,7 @@ static ssize_t sel_write_load(struct file *file, const char __user *buf,
{
struct selinux_fs_info *fsi = file_inode(file)->i_sb->s_fs_info;
- struct selinux_policy *newpolicy;
+ struct selinux_load_state load_state;
ssize_t length;
void *data = NULL;
@@ -642,19 +642,19 @@ static ssize_t sel_write_load(struct file *file, const char __user *buf,
if (copy_from_user(data, buf, count) != 0)
goto out;
- length = security_load_policy(fsi->state, data, count, &newpolicy);
+ length = security_load_policy(fsi->state, data, count, &load_state);
if (length) {
pr_warn_ratelimited("SELinux: failed to load policy\n");
goto out;
}
- length = sel_make_policy_nodes(fsi, newpolicy);
+ length = sel_make_policy_nodes(fsi, load_state.policy);
if (length) {
- selinux_policy_cancel(fsi->state, newpolicy);
+ selinux_policy_cancel(fsi->state, &load_state);
goto out;
}
- selinux_policy_commit(fsi->state, newpolicy);
+ selinux_policy_commit(fsi->state, &load_state);
length = count;
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 5e08ce2c5994..fada4ebc7ef8 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2157,8 +2157,13 @@ static void selinux_policy_cond_free(struct selinux_policy *policy)
kfree(policy);
}
+struct selinux_policy_convert_data {
+ struct convert_context_args args;
+ struct sidtab_convert_params sidtab_params;
+};
+
void selinux_policy_cancel(struct selinux_state *state,
- struct selinux_policy *policy)
+ struct selinux_load_state *load_state)
{
struct selinux_policy *oldpolicy;
@@ -2166,7 +2171,8 @@ void selinux_policy_cancel(struct selinux_state *state,
lockdep_is_held(&state->policy_mutex));
sidtab_cancel_convert(oldpolicy->sidtab);
- selinux_policy_free(policy);
+ selinux_policy_free(load_state->policy);
+ kfree(load_state->convert_data);
}
static void selinux_notify_policy_change(struct selinux_state *state,
@@ -2181,9 +2187,9 @@ static void selinux_notify_policy_change(struct selinux_state *state,
}
void selinux_policy_commit(struct selinux_state *state,
- struct selinux_policy *newpolicy)
+ struct selinux_load_state *load_state)
{
- struct selinux_policy *oldpolicy;
+ struct selinux_policy *oldpolicy, *newpolicy = load_state->policy;
u32 seqno;
oldpolicy = rcu_dereference_protected(state->policy,
@@ -2223,6 +2229,7 @@ void selinux_policy_commit(struct selinux_state *state,
/* Free the old policy */
synchronize_rcu();
selinux_policy_free(oldpolicy);
+ kfree(load_state->convert_data);
/* Notify others of the policy change */
selinux_notify_policy_change(state, seqno);
@@ -2239,11 +2246,10 @@ void selinux_policy_commit(struct selinux_state *state,
* loading the new policy.
*/
int security_load_policy(struct selinux_state *state, void *data, size_t len,
- struct selinux_policy **newpolicyp)
+ struct selinux_load_state *load_state)
{
struct selinux_policy *newpolicy, *oldpolicy;
- struct sidtab_convert_params convert_params;
- struct convert_context_args args;
+ struct selinux_policy_convert_data *convert_data;
int rc = 0;
struct policy_file file = { data, len }, *fp = &file;
@@ -2273,10 +2279,10 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len,
goto err_mapping;
}
-
if (!selinux_initialized(state)) {
/* First policy load, so no need to preserve state from old policy */
- *newpolicyp = newpolicy;
+ load_state->policy = newpolicy;
+ load_state->convert_data = NULL;
return 0;
}
@@ -2290,29 +2296,38 @@ int security_load_policy(struct selinux_state *state, void *data, size_t len,
goto err_free_isids;
}
+ convert_data = kmalloc(sizeof(*convert_data), GFP_KERNEL);
+ if (!convert_data) {
+ rc = -ENOMEM;
+ goto err_free_isids;
+ }
+
/*
* Convert the internal representations of contexts
* in the new SID table.
*/
- args.state = state;
- args.oldp = &oldpolicy->policydb;
- args.newp = &newpolicy->policydb;
+ convert_data->args.state = state;
+ convert_data->args.oldp = &oldpolicy->policydb;
+ convert_data->args.newp = &newpolicy->policydb;
- convert_params.func = convert_context;
- convert_params.args = &args;
- convert_params.target = newpolicy->sidtab;
+ convert_data->sidtab_params.func = convert_context;
+ convert_data->sidtab_params.args = &convert_data->args;
+ convert_data->sidtab_params.target = newpolicy->sidtab;
- rc = sidtab_convert(oldpolicy->sidtab, &convert_params);
+ rc = sidtab_convert(oldpolicy->sidtab, &convert_data->sidtab_params);
if (rc) {
pr_err("SELinux: unable to convert the internal"
" representation of contexts in the new SID"
" table\n");
- goto err_free_isids;
+ goto err_free_convert_data;
}
- *newpolicyp = newpolicy;
+ load_state->policy = newpolicy;
+ load_state->convert_data = convert_data;
return 0;
+err_free_convert_data:
+ kfree(convert_data);
err_free_isids:
sidtab_destroy(newpolicy->sidtab);
err_mapping:
--
2.29.2
