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Subject: [PATCH 1/7] keys: sparse: Fix key_fs[ug]id_changed()
From:   David Howells <dhowells@redhat.com>
To:     keyrings@vger.kernel.org
Cc:     dhowells@redhat.com, linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Wed, 22 May 2019 23:28:10 +0100
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Sparse warnings are incurred by key_fs[ug]id_changed() due to unprotected
accesses of tsk->cred, which is marked __rcu.

Fix this by passing the new cred struct to these functions from
commit_creds() rather than the task pointer.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 include/linux/key.h          |    8 ++++----
 kernel/cred.c                |    4 ++--
 security/keys/process_keys.c |   22 ++++++++++------------
 3 files changed, 16 insertions(+), 18 deletions(-)

diff --git a/include/linux/key.h b/include/linux/key.h
index 7099985e35a9..1f09aad1c98c 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -402,8 +402,8 @@ extern struct ctl_table key_sysctls[];
  * the userspace interface
  */
 extern int install_thread_keyring_to_cred(struct cred *cred);
-extern void key_fsuid_changed(struct task_struct *tsk);
-extern void key_fsgid_changed(struct task_struct *tsk);
+extern void key_fsuid_changed(struct cred *new_cred);
+extern void key_fsgid_changed(struct cred *new_cred);
 extern void key_init(void);
 
 #else /* CONFIG_KEYS */
@@ -418,8 +418,8 @@ extern void key_init(void);
 #define make_key_ref(k, p)		NULL
 #define key_ref_to_ptr(k)		NULL
 #define is_key_possessed(k)		0
-#define key_fsuid_changed(t)		do { } while(0)
-#define key_fsgid_changed(t)		do { } while(0)
+#define key_fsuid_changed(c)		do { } while(0)
+#define key_fsgid_changed(c)		do { } while(0)
 #define key_init()			do { } while(0)
 
 #endif /* CONFIG_KEYS */
diff --git a/kernel/cred.c b/kernel/cred.c
index 45d77284aed0..3bd40de9e192 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -455,9 +455,9 @@ int commit_creds(struct cred *new)
 
 	/* alter the thread keyring */
 	if (!uid_eq(new->fsuid, old->fsuid))
-		key_fsuid_changed(task);
+		key_fsuid_changed(new);
 	if (!gid_eq(new->fsgid, old->fsgid))
-		key_fsgid_changed(task);
+		key_fsgid_changed(new);
 
 	/* do it
 	 * RLIMIT_NPROC limits on user->processes have already been checked
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index f05f7125a7d5..ba5d3172cafe 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -293,28 +293,26 @@ static int install_session_keyring(struct key *keyring)
 /*
  * Handle the fsuid changing.
  */
-void key_fsuid_changed(struct task_struct *tsk)
+void key_fsuid_changed(struct cred *new_cred)
 {
 	/* update the ownership of the thread keyring */
-	BUG_ON(!tsk->cred);
-	if (tsk->cred->thread_keyring) {
-		down_write(&tsk->cred->thread_keyring->sem);
-		tsk->cred->thread_keyring->uid = tsk->cred->fsuid;
-		up_write(&tsk->cred->thread_keyring->sem);
+	if (new_cred->thread_keyring) {
+		down_write(&new_cred->thread_keyring->sem);
+		new_cred->thread_keyring->uid = new_cred->fsuid;
+		up_write(&new_cred->thread_keyring->sem);
 	}
 }
 
 /*
  * Handle the fsgid changing.
  */
-void key_fsgid_changed(struct task_struct *tsk)
+void key_fsgid_changed(struct cred *new_cred)
 {
 	/* update the ownership of the thread keyring */
-	BUG_ON(!tsk->cred);
-	if (tsk->cred->thread_keyring) {
-		down_write(&tsk->cred->thread_keyring->sem);
-		tsk->cred->thread_keyring->gid = tsk->cred->fsgid;
-		up_write(&tsk->cred->thread_keyring->sem);
+	if (new_cred->thread_keyring) {
+		down_write(&new_cred->thread_keyring->sem);
+		new_cred->thread_keyring->gid = new_cred->fsgid;
+		up_write(&new_cred->thread_keyring->sem);
 	}
 }