Messages in this thread | | | Date | Thu, 30 Oct 2014 21:36:18 -0400 | From | Richard Guy Briggs <> | Subject | Re: [PATCH] lsm: get comm using lock to avoid race in string printing |
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On 14/10/30, Paul Moore wrote: > On Friday, September 19, 2014 11:41:15 AM Richard Guy Briggs wrote: > > 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@I-love.SAKURA.ne.jp> > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com> > > The above is a bit odd ... is that a "Signed-off-by:" from Tetsuo Handa or a > "From:"?
That was a "Signed-off-by:" that's likely my fault when manually importing Tetsuo's oddly-formed patch email.
> > --- > > 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)]; > > This makes me a bit nervous for a potential race condition between allocation > and use below. How about using TASK_COMM_LEN instead?
I don't have a strong opinion. Both should work since tsk->comm is defined as "char comm[TASK_COMM_LEN];" in struct task_struct.
> > /* > > * 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; > > paul moore
- RGB
-- Richard Guy Briggs <rbriggs@redhat.com> Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat Remote, Ottawa, Canada Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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