[PATCH 3/3] vhost: fix mmap error check in VDUSE IOTLB miss handler

[Maxime Coquelin <maxime.coquelin@redhat.com>]

The mmap() function returns MAP_FAILED on failure, not NULL.
The current check for !mmap_addr will never detect mmap failures.

When mmap fails but the error is not detected, an invalid address (-1)
is inserted into the IOTLB cache via vhost_user_iotlb_cache_insert().
Subsequent attempts to access this address will cause memory
corruption or crash.

Fix by checking for MAP_FAILED instead of NULL. Also add strerror to
the error message for easier debugging.

Fixes: f27d5206c598 ("vhost: add VDUSE callback for IOTLB miss")
Cc: stable@dpdk.org

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 lib/vhost/vduse.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/lib/vhost/vduse.c b/lib/vhost/vduse.c
index 897dee9f1b..0b5d158fee 100644
--- a/lib/vhost/vduse.c
+++ b/lib/vhost/vduse.c
@@ -86,9 +86,10 @@ vduse_iotlb_miss(struct virtio_net *dev, uint64_t iova, uint8_t perm __rte_unuse
 
 	size = entry.last - entry.start + 1;
 	mmap_addr = mmap(0, size + entry.offset, entry.perm, MAP_SHARED, fd, 0);
-	if (!mmap_addr) {
+	if (mmap_addr == MAP_FAILED) {
 		VHOST_CONFIG_LOG(dev->ifname, ERR,
-				"Failed to mmap IOTLB entry for 0x%" PRIx64, iova);
+				"Failed to mmap IOTLB entry for 0x%" PRIx64 ": %s",
+				iova, strerror(errno));
 		ret = -1;
 		goto close_fd;
 	}
-- 
2.52.0