2013-04-08 03:27:40

by Chen Gang

Subject: [PATCH] kernel: tsacct: strncpy, always be sure of NUL terminated.

for NUL terminated string, always set '\0' at the end.

Signed-off-by: Chen Gang <[email protected]>
---
kernel/tsacct.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index a1dd9a1..01bcc4e 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -78,7 +78,8 @@ void bacct_add_tsk(struct user_namespace *user_ns,
stats->ac_minflt = tsk->min_flt;
stats->ac_majflt = tsk->maj_flt;

- strncpy(stats->ac_comm, tsk->comm, sizeof(stats->ac_comm));
+ strncpy(stats->ac_comm, tsk->comm, sizeof(stats->ac_comm) - 1);
+ stats->ac_comm[sizeof(stats->ac_comm) - 1] = '\0';
}


--
1.7.7.6

2013-04-08 03:52:57

by KOSAKI Motohiro

Subject: Re: [PATCH] kernel: tsacct: strncpy, always be sure of NUL terminated.

On Sun, Apr 7, 2013 at 11:27 PM, Chen Gang <[email protected]> wrote:
>
> for NUL terminated string, always set '\0' at the end.
>
> Signed-off-by: Chen Gang <[email protected]>
> ---
> kernel/tsacct.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/tsacct.c b/kernel/tsacct.c
> index a1dd9a1..01bcc4e 100644
> --- a/kernel/tsacct.c
> +++ b/kernel/tsacct.c
> @@ -78,7 +78,8 @@ void bacct_add_tsk(struct user_namespace *user_ns,
> stats->ac_minflt = tsk->min_flt;
> stats->ac_majflt = tsk->maj_flt;
>
> - strncpy(stats->ac_comm, tsk->comm, sizeof(stats->ac_comm));
> + strncpy(stats->ac_comm, tsk->comm, sizeof(stats->ac_comm) - 1);
> + stats->ac_comm[sizeof(stats->ac_comm) - 1] = '\0';

sizeof(tsk->comm) is 16 and sizeof(stats->ac_comm) is 32. then this statement
is strange. and set_task_comm ensure tsk->comm is nul-terminated.

so your code never change the behavior, right?

And, If buggy driver change tsk->comm not to use set_task_comm and tsk->comm
is not nul-terminated, strncpy() still touch unrelated memory and ac_comm may
expose kernel internal info. that's bad.

2013-04-08 04:04:27

by Chen Gang

Subject: Re: [PATCH] kernel: tsacct: strncpy, always be sure of NUL terminated.

On 2013年04月08日 11:52, KOSAKI Motohiro wrote:
> On Sun, Apr 7, 2013 at 11:27 PM, Chen Gang <[email protected]> wrote:
>> >
>> > for NUL terminated string, always set '\0' at the end.
>> >
>> > Signed-off-by: Chen Gang <[email protected]>
>> > ---
>> > kernel/tsacct.c | 3 ++-
>> > 1 files changed, 2 insertions(+), 1 deletions(-)
>> >
>> > diff --git a/kernel/tsacct.c b/kernel/tsacct.c
>> > index a1dd9a1..01bcc4e 100644
>> > --- a/kernel/tsacct.c
>> > +++ b/kernel/tsacct.c
>> > @@ -78,7 +78,8 @@ void bacct_add_tsk(struct user_namespace *user_ns,
>> > stats->ac_minflt = tsk->min_flt;
>> > stats->ac_majflt = tsk->maj_flt;
>> >
>> > - strncpy(stats->ac_comm, tsk->comm, sizeof(stats->ac_comm));
>> > + strncpy(stats->ac_comm, tsk->comm, sizeof(stats->ac_comm) - 1);
>> > + stats->ac_comm[sizeof(stats->ac_comm) - 1] = '\0';
> sizeof(tsk->comm) is 16 and sizeof(stats->ac_comm) is 32. then this statement
> is strange. and set_task_comm ensure tsk->comm is nul-terminated.
>
> so your code never change the behavior, right?
>

right.

thank you for your information:
originally, I really did not check the sizeof details.


> And, If buggy driver change tsk->comm not to use set_task_comm and tsk->comm
> is not nul-terminated, strncpy() still touch unrelated memory and ac_comm may
> expose kernel internal info. that's bad.
>
>

really, that's bad !

thank you for your information:
originally, I did not think of a buggy driver can change tsk->comm.


:-)

--
Chen Gang

Asianux Corporation