[Linux-kernel-mentees] [PATCH net] net/smc: Prevent kernel-infoleak in __smc_diag_dump()

__smc_diag_dump() is potentially copying uninitialized kernel stack memory
into socket buffers, since the compiler may leave a 4-byte hole near the
beginning of `struct smcd_diag_dmbinfo`. Fix it by initializing `dinfo`
with memset().

Cc: stable@vger.kernel.org
Fixes: 4b1b7d3b30a6 ("net/smc: add SMC-D diag support")
Suggested-by: Dan Carpenter <redacted>
Signed-off-by: Peilin Ye <redacted>
---
Reference: https://lwn.net/Articles/417989/

$ pahole -C "smcd_diag_dmbinfo" net/smc/smc_diag.o
struct smcd_diag_dmbinfo {
	__u32                      linkid;               /*     0     4 */

	/* XXX 4 bytes hole, try to pack */

	__u64                      peer_gid __attribute__((__aligned__(8))); /*     8     8 */
	__u64                      my_gid __attribute__((__aligned__(8))); /*    16     8 */
	__u64                      token __attribute__((__aligned__(8))); /*    24     8 */
	__u64                      peer_token __attribute__((__aligned__(8))); /*    32     8 */

	/* size: 40, cachelines: 1, members: 5 */
	/* sum members: 36, holes: 1, sum holes: 4 */
	/* forced alignments: 4, forced holes: 1, sum forced holes: 4 */
	/* last cacheline: 40 bytes */
} __attribute__((__aligned__(8)));
$ _

 net/smc/smc_diag.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/net/smc/smc_diag.c b/net/smc/smc_diag.c
index e1f64f4ba236..da9ba6d1679b 100644
--- a/net/smc/smc_diag.c
+++ b/net/smc/smc_diag.c

@@ -170,13 +170,15 @@ static int __smc_diag_dump(struct sock *sk, struct sk_buff *skb,
 	    (req->diag_ext & (1 << (SMC_DIAG_DMBINFO - 1))) &&
 	    !list_empty(&smc->conn.lgr->list)) {
 		struct smc_connection *conn = &smc->conn;
-		struct smcd_diag_dmbinfo dinfo = {
-			.linkid = *((u32 *)conn->lgr->id),
-			.peer_gid = conn->lgr->peer_gid,
-			.my_gid = conn->lgr->smcd->local_gid,
-			.token = conn->rmb_desc->token,
-			.peer_token = conn->peer_token
-		};
+		struct smcd_diag_dmbinfo dinfo;
+
+		memset(&dinfo, 0, sizeof(dinfo));
+
+		dinfo.linkid = *((u32 *)conn->lgr->id);
+		dinfo.peer_gid = conn->lgr->peer_gid;
+		dinfo.my_gid = conn->lgr->smcd->local_gid;
+		dinfo.token = conn->rmb_desc->token;
+		dinfo.peer_token = conn->peer_token;
 
 		if (nla_put(skb, SMC_DIAG_DMBINFO, sizeof(dinfo), &dinfo) < 0)
 			goto errout;

-- 
2.25.1

On 8/1/20 9:44 PM, Peilin Ye wrote:

__smc_diag_dump() is potentially copying uninitialized kernel stack memory
into socket buffers, since the compiler may leave a 4-byte hole near the
beginning of `struct smcd_diag_dmbinfo`. Fix it by initializing `dinfo`
with memset().

Cc: stable@vger.kernel.org
Fixes: 4b1b7d3b30a6 ("net/smc: add SMC-D diag support")
Suggested-by: Dan Carpenter <redacted>
Signed-off-by: Peilin Ye <redacted>
---
Reference: https://lwn.net/Articles/417989/

$ pahole -C "smcd_diag_dmbinfo" net/smc/smc_diag.o
struct smcd_diag_dmbinfo {
	__u32                      linkid;               /*     0     4 */

	/* XXX 4 bytes hole, try to pack */

	__u64                      peer_gid __attribute__((__aligned__(8))); /*     8     8 */
	__u64                      my_gid __attribute__((__aligned__(8))); /*    16     8 */
	__u64                      token __attribute__((__aligned__(8))); /*    24     8 */
	__u64                      peer_token __attribute__((__aligned__(8))); /*    32     8 */

	/* size: 40, cachelines: 1, members: 5 */
	/* sum members: 36, holes: 1, sum holes: 4 */
	/* forced alignments: 4, forced holes: 1, sum forced holes: 4 */
	/* last cacheline: 40 bytes */
} __attribute__((__aligned__(8)));
$ _

Thanks, patch is added to our local library and will be part of our
next shipment of smc patches for the net-tree.

Regards, Ursula