Messages in this thread Patch in this message | | | From | Ziyang Xuan <> | Subject | [PATCH net] net: tun: limit first seg size to avoid oversized linearization | Date | Wed, 7 Sep 2022 09:56:18 +0800 |
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Recently, we found a syzkaller problem as following:
======================================================== WARNING: CPU: 1 PID: 17965 at mm/page_alloc.c:5295 __alloc_pages+0x1308/0x16c4 mm/page_alloc.c:5295 ... Call trace: __alloc_pages+0x1308/0x16c4 mm/page_alloc.c:5295 __alloc_pages_node include/linux/gfp.h:550 [inline] alloc_pages_node include/linux/gfp.h:564 [inline] kmalloc_large_node+0x94/0x350 mm/slub.c:4038 __kmalloc_node_track_caller+0x620/0x8e4 mm/slub.c:4545 __kmalloc_reserve.constprop.0+0x1e4/0x2b0 net/core/skbuff.c:151 pskb_expand_head+0x130/0x8b0 net/core/skbuff.c:1654 __skb_grow include/linux/skbuff.h:2779 [inline] tun_napi_alloc_frags+0x144/0x610 drivers/net/tun.c:1477 tun_get_user+0x31c/0x2010 drivers/net/tun.c:1835 tun_chr_write_iter+0x98/0x100 drivers/net/tun.c:2036
It is because the first seg size of the iov_iter from user space is very big, it is 2147479538 which is bigger than the threshold value for bail out early in __alloc_pages(). And skb->pfmemalloc is true, __kmalloc_reserve() would use pfmemalloc reserves without __GFP_NOWARN flag. Thus we got a warning.
I noticed that non-first segs size are required less than PAGE_SIZE in tun_napi_alloc_frags(). The first seg should not be a special case, and oversized linearization is also unreasonable. Limit the first seg size to PAGE_SIZE to avoid oversized linearization.
Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com> --- drivers/net/tun.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 259b2b84b2b3..7db515f94667 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1454,12 +1454,12 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile, size_t len, const struct iov_iter *it) { + size_t linear = iov_iter_single_seg_count(it); struct sk_buff *skb; - size_t linear; int err; int i; - if (it->nr_segs > MAX_SKB_FRAGS + 1) + if (it->nr_segs > MAX_SKB_FRAGS + 1 || linear > PAGE_SIZE) return ERR_PTR(-EMSGSIZE); local_bh_disable(); @@ -1468,7 +1468,6 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile, if (!skb) return ERR_PTR(-ENOMEM); - linear = iov_iter_single_seg_count(it); err = __skb_grow(skb, linear); if (err) goto free; -- 2.25.1
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