[Qemu-devel] [PATCH v2] ide: ahci: add check before calling dma_memory_unmap

[P J P <ppandit@redhat.com>]

From: Prasad J Pandit <pjp@fedoraproject.org>

When IDE AHCI emulation uses Frame Information Structures(FIS)
engine for data transfer, the mapped FIS buffer address is stored
in a static 'bounce.buffer'. When a request is made to map another
memory region, address_space_map() returns NULL because
'bounce.buffer' is in_use. It leads to a null pointer dereference
error while doing 'dma_memory_unmap'. Add a check to avoid it.

Reported-by: Zuozhi fzz <zuozhi.fzz@alibaba-inc.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/ide/ahci.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

Update as per review
  -> https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg05715.html

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index 17f1cbd..f413a59 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -661,9 +661,11 @@ static bool ahci_map_fis_address(AHCIDevice *ad)
 
 static void ahci_unmap_fis_address(AHCIDevice *ad)
 {
-    dma_memory_unmap(ad->hba->as, ad->res_fis, 256,
-                     DMA_DIRECTION_FROM_DEVICE, 256);
-    ad->res_fis = NULL;
+    if (ad->res_fis) {
+        dma_memory_unmap(ad->hba->as, ad->res_fis, 256,
+                         DMA_DIRECTION_FROM_DEVICE, 256);
+        ad->res_fis = NULL;
+    }
 }
 
 static bool ahci_map_clb_address(AHCIDevice *ad)
@@ -677,9 +679,11 @@ static bool ahci_map_clb_address(AHCIDevice *ad)
 
 static void ahci_unmap_clb_address(AHCIDevice *ad)
 {
-    dma_memory_unmap(ad->hba->as, ad->lst, 1024,
-                     DMA_DIRECTION_FROM_DEVICE, 1024);
-    ad->lst = NULL;
+    if (ad->lst) {
+        dma_memory_unmap(ad->hba->as, ad->lst, 1024,
+                         DMA_DIRECTION_FROM_DEVICE, 1024);
+        ad->lst = NULL;
+    }
 }
 
 static void ahci_write_fis_sdb(AHCIState *s, NCQTransferState *ncq_tfs)
-- 
2.5.0