[Qemu-devel] [PATCH] ide: ahci: add check to avoid null dereference (CVE-2019-12067)

[P J P]

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

AHCI emulator while committing DMA buffer in ahci_commit_buf()
may do a NULL dereference if the command header 'ad->cur_cmd'
is null. Add check to avoid it.

Reported-by: Bugs SysSec <bugs-sys...@rub.de>
Signed-off-by: Prasad J Pandit <p...@fedoraproject.org>
---
 hw/ide/ahci.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index 00ba422a48..9fff94075b 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -1458,8 +1458,10 @@ static void ahci_commit_buf(IDEDMA *dma, uint32_t 
tx_bytes)
 {
     AHCIDevice *ad = DO_UPCAST(AHCIDevice, dma, dma);
 
-    tx_bytes += le32_to_cpu(ad->cur_cmd->status);
-    ad->cur_cmd->status = cpu_to_le32(tx_bytes);
+    if (ad->cur_cmd) {
+        tx_bytes += le32_to_cpu(ad->cur_cmd->status);
+        ad->cur_cmd->status = cpu_to_le32(tx_bytes);
+    }
 }
 
 static int ahci_dma_rw_buf(IDEDMA *dma, int is_write)
-- 
2.21.0