[PATCH v2] i386/sev: Ensure attestation report length is valid before retrieving

[Tyler Fanelli <tfanelli@redhat.com>]

The length of the attestation report buffer is never checked to be
valid before allocation is made. If the length of the report is returned
to be 0, the buffer to retrieve the attestation buffer is allocated with
length 0 and passed to the kernel to fill with contents of the attestation
report. Leaving this unchecked is dangerous and could lead to undefined
behavior.

Signed-off-by: Tyler Fanelli <tfanelli@redhat.com>
---
 target/i386/sev.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/target/i386/sev.c b/target/i386/sev.c
index 025ff7a6f8..80d958369b 100644
--- a/target/i386/sev.c
+++ b/target/i386/sev.c
@@ -616,6 +616,8 @@ static SevAttestationReport *sev_get_attestation_report(const char *mnonce,
         return NULL;
     }
 
+    input.len = 0;
+
     /* Query the report length */
     ret = sev_ioctl(sev->sev_fd, KVM_SEV_GET_ATTESTATION_REPORT,
             &input, &err);
@@ -626,6 +628,11 @@ static SevAttestationReport *sev_get_attestation_report(const char *mnonce,
                        ret, err, fw_error_to_str(err));
             return NULL;
         }
+    } else if (input.len == 0) {
+        error_setg(errp, "SEV: Failed to query attestation report:"
+                         " length returned=%d",
+                   input.len);
+        return NULL;
     }
 
     data = g_malloc(input.len);
-- 
2.31.1