[Qemu-devel] [PATCH 49/53] block: vpc - prevent overflow if max_table_entries >= 0x40000000

[Michael Roth <mdroth@linux.vnet.ibm.com>]

From: Jeff Cody <jcody@redhat.com>

When we allocate the pagetable based on max_table_entries, we multiply
the max table entry value by 4 to accomodate a table of 32-bit integers.
However, max_table_entries is a uint32_t, and the VPC driver accepts
ranges for that entry over 0x40000000.  So during this allocation:

s->pagetable = qemu_try_blockalign(bs->file, s->max_table_entries * 4);

The size arg overflows, allocating significantly less memory than
expected.

Since qemu_try_blockalign() size argument is size_t, cast the
multiplication correctly to prevent overflow.

The value of "max_table_entries * 4" is used elsewhere in the code as
well, so store the correct value for use in all those cases.

We also check the Max Tables Entries value, to make sure that it is <
SIZE_MAX / 4, so we know the pagetable size will fit in size_t.

Cc: qemu-stable@nongnu.org
Reported-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit b15deac79530d818092cb49a8021bcce83d71b5b)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 block/vpc.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/block/vpc.c b/block/vpc.c
index 43e768e..8ab30d6 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -168,6 +168,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
     uint8_t buf[HEADER_SIZE];
     uint32_t checksum;
     uint64_t computed_size;
+    uint64_t pagetable_size;
     int disk_type = VHD_DYNAMIC;
     int ret;
 
@@ -269,7 +270,17 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
             goto fail;
         }
 
-        s->pagetable = qemu_try_blockalign(bs->file, s->max_table_entries * 4);
+        if (s->max_table_entries > SIZE_MAX / 4 ||
+            s->max_table_entries > (int) INT_MAX / 4) {
+            error_setg(errp, "Max Table Entries too large (%" PRId32 ")",
+                        s->max_table_entries);
+            ret = -EINVAL;
+            goto fail;
+        }
+
+        pagetable_size = (uint64_t) s->max_table_entries * 4;
+
+        s->pagetable = qemu_try_blockalign(bs->file, pagetable_size);
         if (s->pagetable == NULL) {
             ret = -ENOMEM;
             goto fail;
@@ -277,14 +288,13 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
 
         s->bat_offset = be64_to_cpu(dyndisk_header->table_offset);
 
-        ret = bdrv_pread(bs->file, s->bat_offset, s->pagetable,
-                         s->max_table_entries * 4);
+        ret = bdrv_pread(bs->file, s->bat_offset, s->pagetable, pagetable_size);
         if (ret < 0) {
             goto fail;
         }
 
         s->free_data_block_offset =
-            (s->bat_offset + (s->max_table_entries * 4) + 511) & ~511;
+            ROUND_UP(s->bat_offset + pagetable_size, 512);
 
         for (i = 0; i < s->max_table_entries; i++) {
             be32_to_cpus(&s->pagetable[i]);
-- 
1.9.1