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Subjectslob: Check for NULL pointer before calling ctor()
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While doing some code inspection, I noticed that the slob constructor
method can be called with a NULL pointer. If memory is tight and slob
fails to allocate with slob_alloc() or slob_new_pages() it still calls
the ctor() method with a NULL pointer. Looking at the first ctor()
method I found, I noticed that it can not handle a NULL pointer (I'm
sure others probably can't either):

static void sighand_ctor(void *data)
{
struct sighand_struct *sighand = data;

spin_lock_init(&sighand->siglock);
init_waitqueue_head(&sighand->signalfd_wqh);
}

The solution is to only call the ctor() method if allocation succeeded.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/mm/slob.c b/mm/slob.c
index a99fdf7..48fcb90 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -554,7 +554,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
flags, node);
}

- if (c->ctor)
+ if (b && c->ctor)
c->ctor(b);

kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);



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