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block/cloop: prevent offsets_size integer overflow (CVE-2014-0143) 

The following integer overflow in offsets_size can lead to out-of-bounds
memory stores when n_blocks has a huge value:

    uint32_t n_blocks, offsets_size;
    [...]
    ret = bdrv_pread(bs->file, 128 + 4, &s->n_blocks, 4);
    [...]
    s->n_blocks = be32_to_cpu(s->n_blocks);

    /* read offsets */
    offsets_size = s->n_blocks * sizeof(uint64_t);
    s->offsets = g_malloc(offsets_size);

    [...]

    for(i=0;i<s->n_blocks;i++) {
        s->offsets[i] = be64_to_cpu(s->offsets[i]);

offsets_size can be smaller than n_blocks due to integer overflow.
Therefore s->offsets[] is too small when the for loop byteswaps offsets.

This patch refuses to open files if offsets_size would overflow.

Note that changing the type of offsets_size is not a fix since 32-bit
hosts still only have 32-bit size_t.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2014-03-26 13:05:26 +01:00
parent d65f97a82c
commit 509a41bab5
3 changed files with 18 additions and 0 deletions
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7
block/cloop.c
View File

@ -99,6 +99,13 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
s->n_blocks = be32_to_cpu(s->n_blocks);
/* read offsets */
if (s->n_blocks > UINT32_MAX / sizeof(uint64_t)) {
/* Prevent integer overflow */
error_setg(errp, "n_blocks %u must be %zu or less",
s->n_blocks,
UINT32_MAX / sizeof(uint64_t));
return -EINVAL;
}
offsets_size = s->n_blocks * sizeof(uint64_t);
s->offsets = g_malloc(offsets_size);

7
tests/qemu-iotests/075
View File

@ -43,6 +43,7 @@ _supported_proto generic
_supported_os Linux
block_size_offset=128
n_blocks_offset=132
echo
echo "== check that the first sector can be read =="
@ -67,6 +68,12 @@ _use_sample_img simple-pattern.cloop.bz2
poke_file "$TEST_IMG" "$block_size_offset" "\xff\xff\xfe\x00"
$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
echo
echo "== offsets_size overflow ==="
_use_sample_img simple-pattern.cloop.bz2
poke_file "$TEST_IMG" "$n_blocks_offset" "\xff\xff\xff\xff"
$QEMU_IO -c "read 0 512" $TEST_IMG 2>&1 | _filter_qemu_io | _filter_testdir
# success, all done
echo "*** done"
rm -f $seq.full

4
tests/qemu-iotests/075.out
View File

@ -15,4 +15,8 @@ no file open, try 'help open'
== huge block_size ===
qemu-io: can't open device TEST_DIR/simple-pattern.cloop: block_size 4294966784 must be 64 MB or less
no file open, try 'help open'
== offsets_size overflow ===
qemu-io: can't open device TEST_DIR/simple-pattern.cloop: n_blocks 4294967295 must be 536870911 or less
no file open, try 'help open'
*** done