On 2018年02月08日 12:52, Michael S. Tsirkin wrote:
On Thu, Feb 08, 2018 at 11:59:25AM +0800, Jason Wang wrote:
We need limit the maximum size of queue, otherwise it may cause
several side effects e.g slab will warn when the size exceeds
KMALLOC_MAX_SIZE. Using KMALLOC_MAX_SIZE still looks too so this patch
tries to limit it to 64K. This value could be revisited if we found a
real case that needs more.
Reported-by: syzbot+e4d4f9ddd42955397...@syzkaller.appspotmail.com
Fixes: 2e0ab8ca83c12 ("ptr_ring: array based FIFO for pointers")
Signed-off-by: Jason Wang <jasow...@redhat.com>
---
include/linux/ptr_ring.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 2af71a7..5858d48 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -44,6 +44,8 @@ struct ptr_ring {
void **queue;
};
Seems like a weird location for a define. Either put defines on
top of the file, or near where they are used. I prefer the
second option.
Ok.
+#define PTR_RING_MAX_ALLOC 65536
+
I guess it's an arbitrary number. Seems like a sufficiently large one,
but pls add a comment so readers don't wonder. And please explain what
it does:
/* Callers can create ptr_ring structures with userspace-supplied
* parameters. This sets a limit on the size to make that usecase
* safe. If you ever change this, make sure to audit all callers.
*/
Also I think we should generally use either hex 0x10000 or (1 << 16).
I agree the number is arbitrary, so I still prefer the KMALLOC_MAX_SIZE
especially consider it was used by pfifo_fast now. Try to limit it to an
arbitrary may break lots of exist setups. E.g just google "txqueuelen
100000" can give me a lots of search results.
We can do any kind of optimization on top but not for -net now.
Thanks
/* Note: callers invoking this in a loop must use a compiler barrier,
* for example cpu_relax().
*
@@ -466,6 +468,8 @@ static inline int ptr_ring_consume_batched_bh(struct
ptr_ring *r,
static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp)
{
+ if (size > PTR_RING_MAX_ALLOC)
+ return NULL;
return kvmalloc_array(size, sizeof(void *), gfp | __GFP_ZERO);
}
--
2.7.4
