[PATCH 2/2] ocfs2: validate lengths in dlm_mig_lockres_handler

[Bryam Vargas via B4 Relay]

From: Bryam Vargas <hexlabsecurity@xxxxxxxxx>

A node receiving a DLM_MIG_LOCKRES message trusts several fields of the
peer-supplied dlm_migratable_lockres without validation.  num_locks and
lockname_len are bounded only on the sending side, and the message is
never checked to actually carry num_locks migratable_lock entries.  As a
result dlm_process_recovery_data() walks mres->ml[0..num_locks) past the
kmalloc(data_len) copy of the message (an out-of-bounds read that ends in
a BUG_ON panic), and dlm_init_lockres() copies lockname_len bytes into the
fixed 32-byte o2dlm_lockname slab object (a heap out-of-bounds write).
Both are reachable by any node in the domain.

Validate these fields right after dlm_grab(), before anything uses them --
including the not-joined error path, which already prints mres->lockname
with the unbounded lockname_len as a %.*s precision.  Reject the message
unless lockname_len <= DLM_LOCKID_NAME_MAX, num_locks <=
DLM_MAX_MIGRATABLE_LOCKS (the bound the sender already asserts), and the
payload is large enough to hold the claimed locks.  Conforming recovery
and migration messages are unaffected.

Fixes: 6714d8e86bf4 ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Bryam Vargas <hexlabsecurity@xxxxxxxxx>
---
 fs/ocfs2/dlm/dlmrecovery.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
index 128872bd945d..14d4c7c3eebd 100644
--- a/fs/ocfs2/dlm/dlmrecovery.c
+++ b/fs/ocfs2/dlm/dlmrecovery.c
@@ -1357,6 +1357,15 @@ int dlm_mig_lockres_handler(struct o2net_msg *msg, u32 len, void *data,
 	if (!dlm_grab(dlm))
 		return -EINVAL;
 
+	if (mres->lockname_len > DLM_LOCKID_NAME_MAX ||
+	    mres->num_locks > DLM_MAX_MIGRATABLE_LOCKS ||
+	    be16_to_cpu(msg->data_len) < struct_size(mres, ml, mres->num_locks)) {
+		mlog(ML_ERROR, "%s: invalid lockres migration message from %u\n",
+		     dlm->name, mres->master);
+		dlm_put(dlm);
+		return -EINVAL;
+	}
+
 	if (!dlm_joined(dlm)) {
 		mlog(ML_ERROR, "Domain %s not joined! "
 			  "lockres %.*s, master %u\n",

-- 
2.43.0