netdev - [Linux-kernel-mentees] [PATCH net v2] xdp: Prevent kernel-infoleak in xsk

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Date:   Tue, 28 Jul 2020 01:36:04 -0400
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Song Liu <songliubraving@...com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     Peilin Ye <yepeilin.cs@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        KP Singh <kpsingh@...omium.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [Linux-kernel-mentees] [PATCH net v2] xdp: Prevent kernel-infoleak in xsk_getsockopt()

xsk_getsockopt() is copying uninitialized stack memory to userspace when
`extra_stats` is `false`. Fix it.

Fixes: 8aa5a33578e9 ("xsk: Add new statistics")
Suggested-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Peilin Ye <yepeilin.cs@...il.com>
---
Doing `= {};` is sufficient since currently `struct xdp_statistics` is
defined as follows:

struct xdp_statistics {
	__u64 rx_dropped;
	__u64 rx_invalid_descs;
	__u64 tx_invalid_descs;
	__u64 rx_ring_full;
	__u64 rx_fill_ring_empty_descs;
	__u64 tx_ring_empty_descs;
};

When being copied to the userspace, `stats` will not contain any
uninitialized "holes" between struct fields.

Changes in v2:
    - Remove the "Cc: stable@...r.kernel.org" tag. (Suggested by Song Liu
      <songliubraving@...com>)
    - Initialize `stats` by assignment instead of using memset().
      (Suggested by Song Liu <songliubraving@...com>)

 net/xdp/xsk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 26e3bba8c204..b2b533eddebf 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -840,7 +840,7 @@ static int xsk_getsockopt(struct socket *sock, int level, int optname,
 	switch (optname) {
 	case XDP_STATISTICS:
 	{
-		struct xdp_statistics stats;
+		struct xdp_statistics stats = {};
 		bool extra_stats = true;
 		size_t stats_size;
 
-- 
2.25.1