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authorOndrej Mosnacek <omosnace@redhat.com>2021-03-18 22:53:02 +0100
committerPaul Moore <paul@paul-moore.com>2021-03-18 23:23:46 -0400
commit6406887a12ee5dcdaffff1a8508d91113d545559 (patch)
tree330e72853653a1f8071af6e1cc304ae3ceae304e /security/selinux/selinuxfs.c
parent519dad3bcd809dc1523bf80ab0310ddb3bf00ade (diff)
downloadlinux-stericsson-6406887a12ee5dcdaffff1a8508d91113d545559.tar.gz
selinux: fix variable scope issue in live sidtab conversion
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. Fixes: 02a52c5c8c3b ("selinux: move policy commit after updating selinuxfs") Cc: stable@vger.kernel.org Tested-by: Tyler Hicks <tyhicks@linux.microsoft.com> Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com> [PM: merge fuzz in security.h and services.c] Signed-off-by: Paul Moore <paul@paul-moore.com>
Diffstat (limited to 'security/selinux/selinuxfs.c')
-rw-r--r--security/selinux/selinuxfs.c10
1 files changed, 5 insertions, 5 deletions
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;