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SubjectRe: [PATCH 1/3] kernel/trace/trace.c: introduce missing kfree

* Andrew Morton <akpm@linux-foundation.org> wrote:

> On Fri, 14 Nov 2008 19:05:31 +0100 (CET)
> Julia Lawall <julia@diku.dk> wrote:
>
> > From: Julia Lawall <julia@diku.dk>
> >
> > Error handling code following a kzalloc should free the allocated data.
> >
> > The semantic match that finds the problem is as follows:
> > (http://www.emn.fr/x-info/coccinelle/)
> >
> > // <smpl>
> > @r exists@
> > local idexpression x;
> > statement S;
> > expression E;
> > identifier f,l;
> > position p1,p2;
> > expression *ptr != NULL;
> > @@
> >
> > (
> > if ((x@p1 = \(kmalloc\|kzalloc\|kcalloc\)(...)) == NULL) S
> > |
> > x@p1 = \(kmalloc\|kzalloc\|kcalloc\)(...);
> > ...
> > if (x == NULL) S
> > )
> > <... when != x
> > when != if (...) { <+...x...+> }
> > x->f = E
> > ...>
> > (
> > return \(0\|<+...x...+>\|ptr\);
> > |
> > return@p2 ...;
> > )
> >
> > @script:python@
> > p1 << r.p1;
> > p2 << r.p2;
> > @@
> >
> > print "* file: %s kmalloc %s return %s" % (p1[0].file,p1[0].line,p2[0].line)
> > // </smpl>
> >
> > Signed-off-by: Julia Lawall <julia@diku.dk>
> > ---
> > kernel/trace/trace.c | 1 +
> > 1 files changed, 1 insertions(+), 0 deletions(-)
> >
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 697eda3..d86e325 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -1936,6 +1936,7 @@ __tracing_open(struct inode *inode, struct file *file, int *ret)
> > ring_buffer_read_finish(iter->buffer_iter[cpu]);
> > }
> > mutex_unlock(&trace_types_lock);
> > + kfree(iter);
> >
> > return ERR_PTR(-ENOMEM);
> > }
>
> Nobody seems to have applied this to anything yet?

it's in tip/tracing/urgent:

0bb943c: tracing: kernel/trace/trace.c: introduce missing kfree()

> That function really needs help. Sometimes it will return NULL and
> will set *ret. Other times it will return ERR_PTR(-ENOMEM) and will
> fail to write anything to *ret. One caller (tracing_open) ignores
> the return value. Another caller (tracing_lt_open) tests the
> possibly-uninitialised `ret' and then blindly dereferences the
> possibly-IS_ERR return value.
>
> Or something like that. I looked at it long enough to convince
> myself that it needs fixing ;)

agreed, it's messy. At minimum the ordering is wrong: it should not
return the iterator but 'ret' - the _iterator_ value can then be a
side-effect (dependent on the return value being fine).

the usage site clearly shows the problem:

static int tracing_open(struct inode *inode, struct file *file)
{
int ret;

__tracing_open(inode, file, &ret);

return ret;
}

that could then be a simple:

static int tracing_open(struct inode *inode, struct file *file)
{
return __tracing_open(inode, file, NULL);
}

and we wouldnt allocate an iterator if the iter ptr is NULL. (which we
seem to leak in tracing_open() right now!)

Ingo


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