On Thu, Dec 13, 2018 at 11:39:25AM -0500, Joe Lawrence wrote:
> On 12/13/2018 10:39 AM, Nicholas Mc Guire wrote:
> > On Thu, Dec 13, 2018 at 09:14:18AM -0500, Joe Lawrence wrote:
> >> On 12/13/2018 09:05 AM, Nicholas Mc Guire wrote:
> >>> kzalloc() return should be checked. On dummy_alloc() failing
> >>> in kzalloc() NULL should be returned.
> >>>
> >>> Signed-off-by: Nicholas Mc Guire <hofrat@xxxxxxxxx>
> >>> ---
> >>>
> >>> Problem was located with an experimental coccinelle script
> >>>
> >>> V2: returning NULL is ok but not without cleanup - thanks to
> >>> Petr Mladek <pmladek@xxxxxxxx> for catching this.
> >>>
> >>> Patch was compile tested with: x86_64_defconfig + FTRACE=y
> >>> FUNCTION_TRACER=y, EXPERT=y, LATENCYTOP=y, SAMPLES=y, SAMPLE_LIVEPATCH=y
> >>> (with a number of unrelated sparse warnings on symbols not being static)
> >>>
> >>> Patch is against 4.20-rc6 (localversion-next is next-20181213)
> >>>
> >>> samples/livepatch/livepatch-shadow-mod.c | 4 ++++
> >>> 1 file changed, 4 insertions(+)
> >>>
> >>> diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
> >>> index 4c54b25..4aa8a88 100644
> >>> --- a/samples/livepatch/livepatch-shadow-mod.c
> >>> +++ b/samples/livepatch/livepatch-shadow-mod.c
> >>> @@ -118,6 +118,10 @@ noinline struct dummy *dummy_alloc(void)
> >>>
> >>> /* Oops, forgot to save leak! */
> >>> leak = kzalloc(sizeof(int), GFP_KERNEL);
> >>> + if (!leak) {
> >>> + kfree(d);
> >>> + return NULL;
> >>> + }
> >>>
> >>> pr_info("%s: dummy @ %p, expires @ %lx\n",
> >>> __func__, d, d->jiffies_expire);
> >>>
> >>
> >> Hi Nicholas,
> >>
> >> Thanks for finding and fixing these up... can we either squash these two
> >> patches into a single commit or give them unique subject lines? Code
> >> looks good (including Petr's suggested fix) otherwise.
> >>
> > yup - makes sense to pop it into a single patch - I assumed that this
> > would not be acceptable - so I actually split it up :)
> > I´ll send a V3 then.
>
> I don't know if there is a hard rule, but I always thought that unique
> subject lines were desired to avoid grep/search confusion.
>
the duplicated subjectline was my mistake
> As far as one or two commits, I'd prefer a single commit since these are
> so small. Personal preference, you could just say that you're fixing
> samples/livepatch as a whole.
>
> >
> > BTW: wanted to fix up the sparse warnings but I think thats not going
> > to be that simple as the functions/structs sparse complains about
> > are actually being shared:
>
> Ok, these are welcome too, separate commit...
>
> > CHECK samples/livepatch/livepatch-shadow-fix1.c
> > samples/livepatch/livepatch-shadow-fix1.c:74:14: warning: symbol 'livepatch_fix1_dummy
> > alloc' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-fix1.c:116:6: warning: symbol 'livepatch_fix1_dummy
> > free' was not declared. Should it be static?
> >
> > CHECK samples/livepatch/livepatch-shadow-mod.c
> > samples/livepatch/livepatch-shadow-mod.c:99:1: warning: symbol 'dummy_list' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-mod.c:100:1: warning: symbol 'dummy_list_mutex' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-mod.c:107:23: warning: symbol 'dummy_alloc' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-mod.c:132:15: warning: symbol 'dummy_free' was not declared. Should it be static?
> > samples/livepatch/livepatch-shadow-mod.c:140:15: warning: symbol 'dummy_check' was not declared. Should it be static?
> >
> > so to clean that appropriate declarations should probably
> > go into a .h file. Technically its maybe not important as this
> > is not production code - it would though be nice if sample
> > code is sparse/smatch/cocci clean.
> >
> > would it be acceptable to clean this up with an additional
> > livepatch-shadow-mod.h ?
>
> I'm not a C language expert, but as I understand it: static functions
> are only a namespacing game for the compiler. So I think it is safe to
> pass around and call function pointers to static functions between
> compilation units. At least I see this throughout the kernel, so that
> is my assumption :)
>
I´m not into the details of livepatch but if I declare e.g. dummy_check
static as proposed by sparse and then check the relocs I no longer see
it:
Without the changes sparse proposes dummy_check is visible
hofrat@debian:~/linux-next/samples/livepatch# readelf --relocs livepatch-shadow-mod.ko | grep dummy_check
000000000193 002f00000002 R_X86_64_PC32 0000000000000110 dummy_check - 4
When I then try to load livepatch-shadow-fix1.ko which does not have
dummy_check in its klp_func array its ok but livepatch-shadow-fix2.ko
wich has an entry will fail to load. So while this may work with other modules
I think in the live-patch case its not that simple due to the inner workings
of resolving symbols via klp_object and klp_func array.
So I´ll leave that sparse cleanup to someone who understand the inner
workinsgs of livepatch - before I make a mess of it....
thx!
hofrat
