ocfs2/dlm: validate qr_numregions in dlm_match_regions()

[ Upstream commit 7ab3fbb ]

Patch series "ocfs2/dlm: fix two bugs in dlm_match_regions()".

In dlm_match_regions(), the qr_numregions field from a DLM_QUERY_REGION
network message is used to drive loops over the qr_regions buffer without
sufficient validation.  This series fixes two issues:

- Patch 1 adds a bounds check to reject messages where qr_numregions
  exceeds O2NM_MAX_REGIONS. The o2net layer only validates message
  byte length; it does not constrain field values, so a crafted message
  can set qr_numregions up to 255 and trigger out-of-bounds reads past
  the 1024-byte qr_regions buffer.

- Patch 2 fixes an off-by-one in the local-vs-remote comparison loop,
  which uses '<=' instead of '<', reading one entry past the valid range
  even when qr_numregions is within bounds.

This patch (of 2):

The qr_numregions field from a DLM_QUERY_REGION network message is used
directly as loop bounds in dlm_match_regions() without checking against
O2NM_MAX_REGIONS.  Since qr_regions is sized for at most O2NM_MAX_REGIONS
(32) entries, a crafted message with qr_numregions > 32 causes
out-of-bounds reads past the qr_regions buffer.

Add a bounds check for qr_numregions before entering the loops.

Link: https://lkml.kernel.org/r/SYBPR01MB7881A334D02ACEE5E0645801AF7BA@SYBPR01MB7881.ausprd01.prod.outlook.com
Link: https://lkml.kernel.org/r/SYBPR01MB788166F524AD04E262E174BEAF7BA@SYBPR01MB7881.ausprd01.prod.outlook.com
Fixes: ea20344 ("ocfs2/dlm: Add message DLM_QUERY_REGION")
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: avasummer

fs/ocfs2/dlm/dlmdomain.c

@@ -980,6 +980,14 @@ static int dlm_match_regions(struct dlm_ctxt *dlm,
 		goto bail;
 	}
 
+	if (qr->qr_numregions > O2NM_MAX_REGIONS) {
+		mlog(ML_ERROR, "Domain %s: Joining node %d has invalid "
+		     "number of heartbeat regions %u\n",
+		     qr->qr_domain, qr->qr_node, qr->qr_numregions);
+		status = -EINVAL;
+		goto bail;
+	}
+
 	r = remote;
 	for (i = 0; i < qr->qr_numregions; ++i) {
 		mlog(0, "Region %.*s\n", O2HB_MAX_REGION_NAME_LEN, r);