[34-longterm 098/247] CRED: Fix BUG() upon security_cred_alloc_blank() failure

Paul Gortmaker
2011-06-23T18:17:10Z

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.
-------------------

commit 2edeaa34a6e3f2c43b667f6c4f7b27944b811695 upstream.

In cred_alloc_blank() since 2.6.32, abort_creds(new) is called with
new->security == NULL and new->magic == 0 when security_cred_alloc_blank()
returns an error. As a result, BUG() will be triggered if SELinux is enabled
or CONFIG_DEBUG_CREDENTIALS=y.

If CONFIG_DEBUG_CREDENTIALS=y, BUG() is called from __invalid_creds() because
cred->magic == 0. Failing that, BUG() is called from selinux_cred_free()
because selinux_cred_free() is not expecting cred->security == NULL. This does
not affect smack_cred_free(), tomoyo_cred_free() or apparmor_cred_free().

Fix these bugs by

(1) Set new->magic before calling security_cred_alloc_blank().

(2) Handle null cred->security in creds_are_invalid() and selinux_cred_free().

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
kernel/cred.c | 12 ++++++++----
security/selinux/hooks.c | 6 +++++-
2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/kernel/cred.c b/kernel/cred.c
index 791c431..9a85aee 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -256,13 +256,13 @@ struct cred *cred_alloc_blank(void)
#endif

atomic_set(&new->usage, 1);
+#ifdef CONFIG_DEBUG_CREDENTIALS
+ new->magic = CRED_MAGIC;
+#endif

if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
goto error;

-#ifdef CONFIG_DEBUG_CREDENTIALS
- new->magic = CRED_MAGIC;
-#endif
return new;

error:
@@ -816,7 +816,11 @@ bool creds_are_invalid(const struct cred *cred)
if (cred->magic != CRED_MAGIC)
return true;
#ifdef CONFIG_SECURITY_SELINUX
- if (selinux_is_enabled()) {
+ /*
+ * cred->security == NULL if security_cred_alloc_blank() or
+ * security_prepare_creds() returned an error.
+ */
+ if (selinux_is_enabled() && cred->security) {
if ((unsigned long) cred->security < PAGE_SIZE)
return true;
if ((*(u32 *)cred->security & 0xffffff00) ==
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 0b459c8..c59c83f 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3256,7 +3256,11 @@ static void selinux_cred_free(struct cred *cred)
{
struct task_security_struct *tsec = cred->security;

- BUG_ON((unsigned long) cred->security < PAGE_SIZE);
+ /*
+ * cred->security == NULL if security_cred_alloc_blank() or
+ * security_prepare_creds() returned an error.
+ */
+ BUG_ON(cred->security && (unsigned long) cred->security < PAGE_SIZE);
cred->security = (void *) 0x7UL;
kfree(tsec);
}
--
1.7.4.4