Re: [PATCH] lsm: get comm using lock to avoid race in string printing

When task->comm is passed directly to audit_log_untrustedstring() without getting a copy or using the task_lock, there is a race that could happen that would output a NULL (\0) in the output string that would effectively truncate the rest of the report text after the comm= field in the audit, losing fields. Use get_task_comm() to get a copy while acquiring the task_lock to prevent this and to prevent the result from being a mixture of old and new values of comm. Tetsuo Handa <penguin-kernel(a)I-love.SAKURA.ne.jp&gt; Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt;

--- I've manually checked for locking issues and found none. I've also enabled all the kernel lock debugging options and it came up clean. security/lsm_audit.c | 5 +++-- 1 files changed, 3 insertions(+), 2 deletions(-) diff --git a/security/lsm_audit.c b/security/lsm_audit.c index 69fdf3b..4773b91 100644 --- a/security/lsm_audit.c +++ b/security/lsm_audit.c @@ -212,6 +212,7 @@ static void dump_common_audit_data(struct audit_buffer *ab, struct common_audit_data *a) { struct task_struct *tsk = current; + char comm[sizeof(tsk->comm)];

/* * To keep stack sizes in check force programers to notice if they @@ -221,7 +222,7 @@ static void dump_common_audit_data(struct audit_buffer *ab, BUILD_BUG_ON(sizeof(a->u) > sizeof(void *)*2); audit_log_format(ab, " pid=%d comm=", task_pid_nr(tsk)); - audit_log_untrustedstring(ab, tsk->comm); + audit_log_untrustedstring(ab, get_task_comm(comm, tsk)); switch (a->type) { case LSM_AUDIT_DATA_NONE: @@ -282,7 +283,7 @@ static void dump_common_audit_data(struct audit_buffer *ab, pid_t pid = task_pid_nr(tsk); if (pid) { audit_log_format(ab, " pid=%d comm=", pid); - audit_log_untrustedstring(ab, tsk->comm); + audit_log_untrustedstring(ab, get_task_comm(comm, tsk)); } } break;