[PATCH v1] RDMA/iwpm: Fix use-after-free in mapping info dump

[Binbin Deng <18983559317@163.com>]

iwpm_send_mapinfo() walks the mapinfo hash table while holding
iwpm_mapinfo_lock, but when the current skb is full it temporarily drops
that lock to send the skb and allocate another one.  The hlist iterator is
not protected across that window:

CPU0                                                CPU1
iwpm_send_mapinfo()
spin_lock_irqsave(&iwpm_mapinfo_lock, flags)
hlist_for_each_entry(..., map_info, ...)
  map_info points at map_info A
  fill the current skb
  spin_unlock_irqrestore(&iwpm_mapinfo_lock,flags)
  send the skb / allocate the next skb
                                                    iwpm_remove_mapinfo()
                                                    spin_lock_irqsave(&iwpm_mapinfo_lock,flags)
                                                    find map_info A
                                                    hlist_del_init(&A->hlist_node)
                                                    kfree(A)
                                                    spin_unlock_irqrestore(&iwpm_mapinfo_lock, flags)
spin_lock_irqsave(&iwpm_mapinfo_lock, flags)
hlist_for_each_entry() reads A->hlist_node.next

CPU0 then resumes an iterator whose object has been freed, producing a
use-after-free.  The race is reachable with many mapped iWARP CM IDs when
the port mapper hello path dumps the mapinfo table concurrently with
teardown of the ID at the iterator position.  It can be reported by KASAN
or lead to memory corruption and a panic.

The spinlock still protects the hash table itself, but it cannot protect
an iterator that is retained across an unlock.  Add a mutex which covers
the complete dump and also serializes individual removal and full-table
cleanup.  The netlink dump and CM ID teardown paths can sleep, so this
outer lock is appropriate.

Found during a static-analysis-assisted audit: candidate sites were
surfaced by a Coccinelle rule, and the reader/writer paths were
confirmed by deep code inspection. Due to a lack of hardware
infrastructure, the issue was not observed at runtime.

Fixes: 30dc5e63d6a5 ("RDMA/core: Add support for iWARP Port Mapper user space service")
Assisted-by: Coccinelle
Signed-off-by: Binbin Deng <18983559317@163.com>
---
 drivers/infiniband/core/iwpm_util.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/infiniband/core/iwpm_util.c b/drivers/infiniband/core/iwpm_util.c
index 51af8c1c49f9..be5c77356c78 100644
--- a/drivers/infiniband/core/iwpm_util.c
+++ b/drivers/infiniband/core/iwpm_util.c
@@ -45,6 +45,8 @@ static DEFINE_SPINLOCK(iwpm_nlmsg_req_lock);
 static struct hlist_head *iwpm_hash_bucket;
 static DEFINE_SPINLOCK(iwpm_mapinfo_lock);
 
+static DEFINE_MUTEX(iwpm_mapinfo_mutex);
+
 static struct hlist_head *iwpm_reminfo_bucket;
 static DEFINE_SPINLOCK(iwpm_reminfo_lock);
 
@@ -159,6 +161,7 @@ int iwpm_remove_mapinfo(struct sockaddr_storage *local_sockaddr,
 	unsigned long flags;
 	int ret = -EINVAL;
 
+	mutex_lock(&iwpm_mapinfo_mutex);
 	spin_lock_irqsave(&iwpm_mapinfo_lock, flags);
 	if (iwpm_hash_bucket) {
 		hash_bucket_head = get_mapinfo_hash_bucket(
@@ -182,6 +185,7 @@ int iwpm_remove_mapinfo(struct sockaddr_storage *local_sockaddr,
 	}
 remove_mapinfo_exit:
 	spin_unlock_irqrestore(&iwpm_mapinfo_lock, flags);
+	mutex_unlock(&iwpm_mapinfo_mutex);
 	return ret;
 }
 
@@ -193,6 +197,7 @@ static void free_hash_bucket(void)
 	int i;
 
 	/* remove all the mapinfo data from the list */
+	mutex_lock(&iwpm_mapinfo_mutex);
 	spin_lock_irqsave(&iwpm_mapinfo_lock, flags);
 	for (i = 0; i < IWPM_MAPINFO_HASH_SIZE; i++) {
 		hlist_for_each_entry_safe(map_info, tmp_hlist_node,
@@ -206,6 +211,7 @@ static void free_hash_bucket(void)
 	kfree(iwpm_hash_bucket);
 	iwpm_hash_bucket = NULL;
 	spin_unlock_irqrestore(&iwpm_mapinfo_lock, flags);
+	mutex_unlock(&iwpm_mapinfo_mutex);
 }
 
 static void free_reminfo_bucket(void)
@@ -654,6 +660,7 @@ int iwpm_send_mapinfo(u8 nl_client, int iwpm_pid)
 		goto send_mapping_info_exit;
 	}
 	skb_num++;
+	mutex_lock(&iwpm_mapinfo_mutex);
 	spin_lock_irqsave(&iwpm_mapinfo_lock, flags);
 	ret = -EINVAL;
 	for (i = 0; i < IWPM_MAPINFO_HASH_SIZE; i++) {
@@ -712,17 +719,20 @@ int iwpm_send_mapinfo(u8 nl_client, int iwpm_pid)
 				skb = NULL;
 				if (ret) {
 					err_str = "Unable to send map info";
+					mutex_unlock(&iwpm_mapinfo_mutex);
 					goto send_mapping_info_exit;
 				}
 				if (skb_num == IWPM_MAPINFO_SKB_COUNT) {
 					ret = -ENOMEM;
 					err_str = "Insufficient skbs for map info";
+					mutex_unlock(&iwpm_mapinfo_mutex);
 					goto send_mapping_info_exit;
 				}
 				skb = dev_alloc_skb(NLMSG_GOODSIZE);
 				if (!skb) {
 					ret = -ENOMEM;
 					err_str = "Unable to allocate skb";
+					mutex_unlock(&iwpm_mapinfo_mutex);
 					goto send_mapping_info_exit;
 				}
 				spin_lock_irqsave(&iwpm_mapinfo_lock, flags);
@@ -731,6 +741,8 @@ int iwpm_send_mapinfo(u8 nl_client, int iwpm_pid)
 	}
 send_mapping_info_unlock:
 	spin_unlock_irqrestore(&iwpm_mapinfo_lock, flags);
+	mutex_unlock(&iwpm_mapinfo_mutex);
+
 send_mapping_info_exit:
 	if (ret) {
 		pr_warn("%s: %s (ret = %d)\n", __func__, err_str, ret);
-- 
2.43.0