Commit 2cf7cfa1 authored by Kevin Wolf's avatar Kevin Wolf Committed by Stefan Hajnoczi
Browse files

qcow2: Catch some L1 table index overflows 

This catches the situation that is described in the bug report at
https://bugs.launchpad.net/qemu/+bug/865518

 and goes like this:

    $ qemu-img create -f qcow2 huge.qcow2 $((1024*1024))T
    Formatting 'huge.qcow2', fmt=qcow2 size=1152921504606846976 encryption=off cluster_size=65536 lazy_refcounts=off
    $ qemu-io /tmp/huge.qcow2 -c "write $((1024*1024*1024*1024*1024*1024 - 1024)) 512"
    Segmentation fault

With this patch applied the segfault will be avoided, however the case
will still fail, though gracefully:

    $ qemu-img create -f qcow2 /tmp/huge.qcow2 $((1024*1024))T
    Formatting 'huge.qcow2', fmt=qcow2 size=1152921504606846976 encryption=off cluster_size=65536 lazy_refcounts=off
    qemu-img: The image size is too large for file format 'qcow2'

Note that even long before these overflow checks kick in, you get
insanely high memory usage (up to INT_MAX * sizeof(uint64_t) = 16 GB for
the L1 table), so with somewhat smaller image sizes you'll probably see
qemu aborting for a failed g_malloc().

If you need huge image sizes, you should increase the cluster size to
the maximum of 2 MB in order to get higher limits.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent b087143b

block/qcow2-cluster.c

+15 −8
Original line number Diff line number Diff line
@@ -29,12 +29,13 @@ 
#include "block/qcow2.h"

#include "trace.h"



int qcow2_grow_l1_table(BlockDriverState *bs, int min_size, bool exact_size)

int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,

                        bool exact_size)

{

    BDRVQcowState *s = bs->opaque;

    int new_l1_size, new_l1_size2, ret, i;

    int new_l1_size2, ret, i;

    uint64_t *new_l1_table;

    int64_t new_l1_table_offset;

    int64_t new_l1_table_offset, new_l1_size;

    uint8_t data[12];



    if (min_size <= s->l1_size)
@@ -53,8 +54,13 @@ int qcow2_grow_l1_table(BlockDriverState *bs, int min_size, bool exact_size) 
        }

    }



    if (new_l1_size > INT_MAX) {

        return -EFBIG;

    }



#ifdef DEBUG_ALLOC2

    fprintf(stderr, "grow l1_table from %d to %d\n", s->l1_size, new_l1_size);

    fprintf(stderr, "grow l1_table from %d to %" PRId64 "\n",

            s->l1_size, new_l1_size);

#endif



    new_l1_size2 = sizeof(uint64_t) * new_l1_size;
@@ -391,8 +397,8 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset, 
    int *num, uint64_t *cluster_offset)

{

    BDRVQcowState *s = bs->opaque;

    unsigned int l1_index, l2_index;

    uint64_t l2_offset, *l2_table;

    unsigned int l2_index;

    uint64_t l1_index, l2_offset, *l2_table;

    int l1_bits, c;

    unsigned int index_in_cluster, nb_clusters;

    uint64_t nb_available, nb_needed;
@@ -507,8 +513,8 @@ static int get_cluster_table(BlockDriverState *bs, uint64_t offset, 
                             int *new_l2_index)

{

    BDRVQcowState *s = bs->opaque;

    unsigned int l1_index, l2_index;

    uint64_t l2_offset;

    unsigned int l2_index;

    uint64_t l1_index, l2_offset;

    uint64_t *l2_table = NULL;

    int ret;
@@ -522,6 +528,7 @@ static int get_cluster_table(BlockDriverState *bs, uint64_t offset, 
        }

    }



    assert(l1_index < s->l1_size);

    l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;



    /* seek the l2 table of the given l2 offset */

block/qcow2.c

+11 −2
Original line number Diff line number Diff line
@@ -307,6 +307,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags) 
    QemuOpts *opts;

    Error *local_err = NULL;

    uint64_t ext_end;

    uint64_t l1_vm_state_index;



    ret = bdrv_pread(bs->file, 0, &header, sizeof(header));

    if (ret < 0) {
@@ -424,7 +425,14 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags) 


    /* read the level 1 table */

    s->l1_size = header.l1_size;

    s->l1_vm_state_index = size_to_l1(s, header.size);



    l1_vm_state_index = size_to_l1(s, header.size);

    if (l1_vm_state_index > INT_MAX) {

        ret = -EFBIG;

        goto fail;

    }

    s->l1_vm_state_index = l1_vm_state_index;



    /* the L1 table must contain at least enough entries to put

       header.size bytes */

    if (s->l1_size < s->l1_vm_state_index) {
@@ -1480,7 +1488,8 @@ static coroutine_fn int qcow2_co_discard(BlockDriverState *bs, 
static int qcow2_truncate(BlockDriverState *bs, int64_t offset)

{

    BDRVQcowState *s = bs->opaque;

    int ret, new_l1_size;

    int64_t new_l1_size;

    int ret;



    if (offset & 511) {

        error_report("The new size must be a multiple of 512");

block/qcow2.h

+3 −2
Original line number Diff line number Diff line
@@ -284,7 +284,7 @@ static inline int size_to_clusters(BDRVQcowState *s, int64_t size) 
    return (size + (s->cluster_size - 1)) >> s->cluster_bits;

}



static inline int size_to_l1(BDRVQcowState *s, int64_t size)

static inline int64_t size_to_l1(BDRVQcowState *s, int64_t size)

{

    int shift = s->cluster_bits + s->l2_bits;

    return (size + (1ULL << shift) - 1) >> shift;
@@ -360,7 +360,8 @@ int qcow2_check_refcounts(BlockDriverState *bs, BdrvCheckResult *res, 
                          BdrvCheckMode fix);



/* qcow2-cluster.c functions */

int qcow2_grow_l1_table(BlockDriverState *bs, int min_size, bool exact_size);

int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,

                        bool exact_size);

void qcow2_l2_cache_reset(BlockDriverState *bs);

int qcow2_decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset);

void qcow2_encrypt_sectors(BDRVQcowState *s, int64_t sector_num,