Hi, thanks for your reply!

On Mon, 2021-03-01 at 14:09 +0100, Eric Dumazet wrote:

On 2/26/21 8:11 PM, Pavel Skripkin wrote:

quoted

syzbot found WARNING in __alloc_pages_nodemask()[1] when order >=
MAX_ORDER.
It was caused by __netdev_alloc_skb(), which doesn't check len
value after adding NET_SKB_PAD.
Order will be >= MAX_ORDER and passed to __alloc_pages_nodemask()
if size > KMALLOC_MAX_SIZE.

static void *kmalloc_large_node(size_t size, gfp_t flags, int node)
{
	struct page *page;
	void *ptr = NULL;
	unsigned int order = get_order(size);
...
	page = alloc_pages_node(node, flags, order);
...

[1] WARNING in __alloc_pages_nodemask+0x5f8/0x730
mm/page_alloc.c:5014
Call Trace:
 __alloc_pages include/linux/gfp.h:511 [inline]
 __alloc_pages_node include/linux/gfp.h:524 [inline]
 alloc_pages_node include/linux/gfp.h:538 [inline]
 kmalloc_large_node+0x60/0x110 mm/slub.c:3999
 __kmalloc_node_track_caller+0x319/0x3f0 mm/slub.c:4496
 __kmalloc_reserve net/core/skbuff.c:150 [inline]
 __alloc_skb+0x4e4/0x5a0 net/core/skbuff.c:210
 __netdev_alloc_skb+0x70/0x400 net/core/skbuff.c:446
 netdev_alloc_skb include/linux/skbuff.h:2832 [inline]
 qrtr_endpoint_post+0x84/0x11b0 net/qrtr/qrtr.c:442
 qrtr_tun_write_iter+0x11f/0x1a0 net/qrtr/tun.c:98
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write+0x426/0x650 fs/read_write.c:518
 vfs_write+0x791/0xa30 fs/read_write.c:605
 ksys_write+0x12d/0x250 fs/read_write.c:658
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported-by: syzbot+80dccaee7c6630fa9dcf@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <redacted>
Change-Id: I480a6d6f818a4c0a387db0cd3f230b68a7daeb16
---
 net/core/skbuff.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 785daff48030..dc28c8f7bf5f 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c

@@ -443,6 +443,9 @@ struct sk_buff *__netdev_alloc_skb(struct

net_device *dev, unsigned int len,
 	if (len <= SKB_WITH_OVERHEAD(1024) ||
 	    len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
 	    (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
+		if (len > KMALLOC_MAX_SIZE)
+			return NULL;
+
 		skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX,
NUMA_NO_NODE);
 		if (!skb)
 			goto skb_fail;

No, please fix the offender instead.

Yesterday I already send newer patch version to Alexander Lobakin,
where I added __GFP_NOWARN in qrtr_endpoint_post(). I think, You can
check it in this thread. 

Offender tentative fix was in 

commit 2a80c15812372e554474b1dba0b1d8e467af295d
Author: Sabyrzhan Tasbolatov [off-list ref]
Date:   Tue Feb 2 15:20:59 2021 +0600

    net/qrtr: restrict user-controlled length in
qrtr_tun_write_iter()

This patch fixes kzalloc() call, but the warning was caused by
__netdev_alloc_skb().  

qrtr maintainers have to tell us what is the maximum datagram length
they need to support.

With regards,
Pavel Skripkin