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smack: fix cred UAF in smack_file_send_sigiotask()

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When inspecting the credentials of another task, objective credentials
(->real_cred, accessed with __task_cred()) must always be used.

Accessing ->cred on a non-current task is forbidden unless that task is
being created or destroyed; a task is allowed to change its own ->cred
pointer with no synchronization, and changing ->cred should only affect the
current syscall.

smack_file_send_sigiotask() was accessing both sets of credentials: First
tsk->cred, then __task_cred(tsk).

Fix it, always access the objective credentials here.

I have tested that this bug can lead to a KASAN-reported UAF of struct cred
in smack_file_send_sigiotask(), and that this fix prevents the race.

Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
This commit is contained in:
Jann Horn 2026-08-06 21:41:35 +02:00 committed by Casey Schaufler
parent a7c44fd9f8
commit fedc88e38c
1 changed files with 1 additions and 1 deletions
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2
security/smack/smack_lsm.c
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@ -1978,7 +1978,7 @@ static int smack_file_send_sigiotask(struct task_struct *tsk,
{
struct smack_known **blob;
struct smack_known *skp;
struct smack_known *tkp = smk_of_task(smack_cred(tsk->cred));
struct smack_known *tkp = smk_of_task_struct_obj(tsk);
const struct cred *tcred;
struct file *file;
int rc;