[PATCH] cpu: Don't access invalid memory in virCPUx86Translate

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

Problem is that if there are no signatures for a CPU, then we
still allocate cpu->signatures (even though with size 0). Later,
we access cpu->signatures[0] if cpu->signatures is not NULL.

 Invalid read of size 4
    at 0x5F439D7: virCPUx86Translate (cpu_x86.c:2930)
    by 0x5F3C239: virCPUTranslate (cpu.c:927)
    by 0x57CE7A1: qemuProcessUpdateGuestCPU (qemu_process.c:5870)
    ...
  Address 0xf752d40 is 0 bytes after a block of size 0 alloc'd
    at 0x4C30EC6: calloc (vg_replace_malloc.c:711)
    by 0x5DBDE4E: virAllocN (viralloc.c:190)
    by 0x5F3E4FA: x86ModelCopySignatures (cpu_x86.c:990)
    by 0x5F3E60F: x86ModelCopy (cpu_x86.c:1008)
    by 0x5F3E7CB: x86ModelFromCPU (cpu_x86.c:1068)
    by 0x5F4397E: virCPUx86Translate (cpu_x86.c:2922)
    by 0x5F3C239: virCPUTranslate (cpu.c:927)
    by 0x57CE7A1: qemuProcessUpdateGuestCPU (qemu_process.c:5870)
    ...
Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>

Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---
 src/cpu/cpu_x86.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/cpu/cpu_x86.c b/src/cpu/cpu_x86.c
index 92941d1287..c8697819ab 100644
--- a/src/cpu/cpu_x86.c
+++ b/src/cpu/cpu_x86.c
@@ -987,6 +987,9 @@ x86ModelCopySignatures(virCPUx86ModelPtr dst,
 {
     size_t i;
 
+    if (src->nsignatures == 0)
+        return 0;
+
     if (VIR_ALLOC_N(dst->signatures, src->nsignatures) < 0)
         return -1;
 
@@ -2926,7 +2929,7 @@ virCPUx86Translate(virCPUDefPtr cpu,
         virCPUx86DataAddCPUIDInt(&model->data, &model->vendor->cpuid) < 0)
         goto cleanup;
 
-    if (model->signatures &&
+    if (model->nsignatures &&
         x86DataAddSignature(&model->data, model->signatures[0]) < 0)
         goto cleanup;
 
-- 
2.19.2

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