Re: [PATCH] kernel: module: strncpy issue, using strlcpy instead of strncpy

Rusty Russell
2013-04-08T14:28:41Z

Chen Gang <gang.chen@asianux.com> writes:
> On 2013年04月08日 13:30, Rusty Russell wrote:
>> Chen Gang <gang.chen@asianux.com> writes:
>>> > ownername and namebuf are all NUL terminated string.
>>> >
>>> > need always let them ended by '\0'.
>>> >
>>> > Signed-off-by: Chen Gang <gang.chen@asianux.com>
>>> > ---
>>> > kernel/module.c | 4 ++--
>>> > 1 files changed, 2 insertions(+), 2 deletions(-)
>>> >
>>> > diff --git a/kernel/module.c b/kernel/module.c
>>> > index 3c2c72d..597efd8 100644
>>> > --- a/kernel/module.c
>>> > +++ b/kernel/module.c
>>> > @@ -1283,7 +1283,7 @@ static const struct kernel_symbol *resolve_symbol(struct module *mod,
>>> >
>>> > getname:
>>> > /* We must make copy under the lock if we failed to get ref. */
>>> > - strncpy(ownername, module_name(owner), MODULE_NAME_LEN);
>>> > + strlcpy(ownername, module_name(owner), MODULE_NAME_LEN);
>> This should just be strcpy().
>>
>
> for me, either strcpy or strlcpy are ok.
> strcpy is quicker than strlcpy (in our case, it seems not quite important).
> strlcpy is more clearer to readers (they do not care about the buffer length again).
>
> since you prefer strcpy, I need respect your (the original maintainer's) willing.
> so I need change to strcpy.
>
> :-)
>
>
>>> > unlock:
>>> > mutex_unlock(&module_mutex);
>>> > return sym;
>>> > @@ -3464,7 +3464,7 @@ const char *module_address_lookup(unsigned long addr,
>>> > }
>>> > /* Make a copy in here where it's safe */
>>> > if (ret) {
>>> > - strncpy(namebuf, ret, KSYM_NAME_LEN - 1);
>>> > + strlcpy(namebuf, ret, KSYM_NAME_LEN);
>> This isn't a bug, because the caller (kallsyms_lookup) puts a NUL in
>> ret[KSYM_NAME_LEN].
>>
>
> originally, it is really not a bug (so subject need delete "strncpy issue").
> now, I still prefer to set tail '\0' in function module_address_lookup.
> future, if it is used by others, it is necessary to set tail '\0' in this function.
>
>
>
> and for this patch, is it suitable to send patch v2 ?

Yes, that's fine.

>> However, kallsyms_lookup also calls kallsyms_expand_symbol, which
>> doesn't stop at KSYM_NAME_LEN, so if a name was longer than that we'd
>> have a real bug.
>>
>> Would you like to take a look at that, too?
>>
>
> it looks like a bug. for me, I prefer to give length check for it.
>
> but I am sorry, now, I can not be sure whether it is really a bug.

It really is. We don't export any symbols > 128 characters, but if we
did then kallsyms_expand_symbol() would overflow the buffer handed to
it.

Your suggestion about an explicit length for kallsyms_expand_symbol() is
the correct one.

(This is a separate patch to the cleanup above).

Thanks,
Rusty.