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[Qemu-devel] [PATCH 3/4] savevm: improve subsections detection on load


From: Juan Quintela
Subject: [Qemu-devel] [PATCH 3/4] savevm: improve subsections detection on load
Date: Tue, 4 Oct 2011 16:38:14 +0200

We add qemu_peek_buffer, that is identical to qemu_get_buffer, just
that it don't update f->buf_index.

We add a paramenter to qemu_peek_byte() to be able to peek more than
one byte.

Once this is done, to see if we have a subsection we look:
- 1st byte is QEMU_VM_SUBSECTION
- 2nd byte is a length, and is bigger than section name
- 3rd element is a string that starts with section_name

So, we shouldn't have false positives (yes, content could still get us
wrong but probabilities are really low).

Signed-off-by: Juan Quintela <address@hidden>
---
 savevm.c |   71 ++++++++++++++++++++++++++++++++++++++++++++++++++++---------
 1 files changed, 60 insertions(+), 11 deletions(-)

diff --git a/savevm.c b/savevm.c
index 5fee4e2..db6ea12 100644
--- a/savevm.c
+++ b/savevm.c
@@ -532,6 +532,37 @@ void qemu_put_byte(QEMUFile *f, int v)
         qemu_fflush(f);
 }

+static int qemu_peek_buffer(QEMUFile *f, uint8_t *buf, int size1, int offset)
+{
+    int size, l;
+    int index = f->buf_index + offset;
+
+    if (f->is_write) {
+        abort();
+    }
+
+    size = size1;
+    while (size > 0) {
+        l = f->buf_size - index;
+        if (l == 0) {
+            qemu_fill_buffer(f);
+            index = f->buf_index + offset;
+            l = f->buf_size - index;
+            if (l == 0) {
+                break;
+            }
+        }
+        if (l > size) {
+            l = size;
+        }
+        memcpy(buf, f->buf + index, l);
+        index += l;
+        buf += l;
+        size -= l;
+    }
+    return size1 - size;
+}
+
 int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size1)
 {
     int size, l;
@@ -561,19 +592,22 @@ int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size1)
     return size1 - size;
 }

-static int qemu_peek_byte(QEMUFile *f)
+static int qemu_peek_byte(QEMUFile *f, int offset)
 {
+    int index = f->buf_index + offset;
+
     if (f->is_write) {
         abort();
     }

-    if (f->buf_index >= f->buf_size) {
+    if (index >= f->buf_size) {
         qemu_fill_buffer(f);
-        if (f->buf_index >= f->buf_size) {
+        index = f->buf_index + offset;
+        if (index >= f->buf_size) {
             return 0;
         }
     }
-    return f->buf[f->buf_index];
+    return f->buf[index];
 }

 int qemu_get_byte(QEMUFile *f)
@@ -1687,22 +1721,37 @@ static int vmstate_subsection_load(QEMUFile *f, const 
VMStateDescription *vmsd,
         return 0;
     }

-    while (qemu_peek_byte(f) == QEMU_VM_SUBSECTION) {
+    while (qemu_peek_byte(f, 0) == QEMU_VM_SUBSECTION) {
         char idstr[256];
         int ret;
-        uint8_t version_id, len;
+        uint8_t version_id, len, size;
         const VMStateDescription *sub_vmsd;

-        qemu_get_byte(f); /* subsection */
-        len = qemu_get_byte(f);
-        qemu_get_buffer(f, (uint8_t *)idstr, len);
-        idstr[len] = 0;
-        version_id = qemu_get_be32(f);
+        len = qemu_peek_byte(f, 1);
+        if (len < strlen(vmsd->name) + 1) {
+            /* subsection name has be be "section_name/a" */
+            return 0;
+        }
+        size = qemu_peek_buffer(f, (uint8_t *)idstr, len, 2);
+        if (size != len) {
+            return 0;
+        }
+        idstr[size] = 0;

+        if (strncmp(vmsd->name, idstr, strlen(vmsd->name)) != 0) {
+            /* it don't have a valid subsection name */
+            return 0;
+        }
         sub_vmsd = vmstate_get_subsection(sub, idstr);
         if (sub_vmsd == NULL) {
             return -ENOENT;
         }
+        qemu_get_byte(f); /* subsection */
+        qemu_get_byte(f); /* len  */
+        qemu_get_buffer(f, (uint8_t *)idstr, len);
+        idstr[len] = 0;
+        version_id = qemu_get_be32(f);
+
         assert(!sub_vmsd->subsections);
         ret = vmstate_load_state(f, sub_vmsd, opaque, version_id);
         if (ret) {
-- 
1.7.6.4




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