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qemu_opts_append: Play nicely with QemuOptsList's head

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When running a libvirt test suite I've noticed the qemu-img is
crashing occasionally. Tracing the problem down led me to the
following valgrind output:

qemu.git $ valgrind -q ./qemu-img create -f qed -obacking_file=/dev/null,backing_fmt=raw qed
==14881== Invalid write of size 8
==14881==    at 0x1D263F: qemu_opts_create (qemu-option.c:692)
==14881==    by 0x130782: bdrv_img_create (block.c:5531)
==14881==    by 0x118DE0: img_create (qemu-img.c:462)
==14881==    by 0x11E7E4: main (qemu-img.c:2830)
==14881==  Address 0x11fedd38 is 24 bytes inside a block of size 232 free'd
==14881==    at 0x4C2CA5E: realloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==14881==    by 0x592D35E: g_realloc (in /usr/lib64/libglib-2.0.so.0.3800.2)
==14881==    by 0x1D38D8: qemu_opts_append (qemu-option.c:1129)
==14881==    by 0x13075E: bdrv_img_create (block.c:5528)
==14881==    by 0x118DE0: img_create (qemu-img.c:462)
==14881==    by 0x11E7E4: main (qemu-img.c:2830)
==14881==
Formatting 'qed', fmt=qed size=0 backing_file='/dev/null' backing_fmt='raw' cluster_size=65536
==14881== Invalid write of size 8
==14881==    at 0x1D28BE: qemu_opts_del (qemu-option.c:750)
==14881==    by 0x130BF3: bdrv_img_create (block.c:5638)
==14881==    by 0x118DE0: img_create (qemu-img.c:462)
==14881==    by 0x11E7E4: main (qemu-img.c:2830)
==14881==  Address 0x11fedd38 is 24 bytes inside a block of size 232 free'd
==14881==    at 0x4C2CA5E: realloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==14881==    by 0x592D35E: g_realloc (in /usr/lib64/libglib-2.0.so.0.3800.2)
==14881==    by 0x1D38D8: qemu_opts_append (qemu-option.c:1129)
==14881==    by 0x13075E: bdrv_img_create (block.c:5528)
==14881==    by 0x118DE0: img_create (qemu-img.c:462)
==14881==    by 0x11E7E4: main (qemu-img.c:2830)
==14881==

The problem is apparently in the qemu_opts_append(). Well, if it
gets called twice or more. On the first call, when @dst is NULL
some initialization is done during which @dst->head list gets
initialized. The list is initialized in a way, so that the list
tail points at the list head. However, the next time
qemu_opts_append() is called for new options to be added,
g_realloc() may move @dst to a new address making the old list tail
point at an invalid address. If that's the case, we must update the
list pointers.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Michal Privoznik 2014-06-25 10:38:41 +02:00 committed by Kevin Wolf
parent 20cca275c6
commit a760715095
1 changed files with 10 additions and 1 deletions
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11
util/qemu-option.c
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@ -1111,6 +1111,7 @@ QemuOptsList *qemu_opts_append(QemuOptsList *dst,
size_t num_opts, num_dst_opts;
QemuOptDesc *desc;
bool need_init = false;
bool need_head_update;
if (!list) {
return dst;
@ -1121,6 +1122,12 @@ QemuOptsList *qemu_opts_append(QemuOptsList *dst,
*/
if (!dst) {
need_init = true;
need_head_update = true;
} else {
/* Moreover, even if dst is not NULL, the realloc may move it to a
* different address in which case we may get a stale tail pointer
* in dst->head. */
need_head_update = QTAILQ_EMPTY(&dst->head);
}
num_opts = count_opts_list(dst);
@ -1131,9 +1138,11 @@ QemuOptsList *qemu_opts_append(QemuOptsList *dst,
if (need_init) {
dst->name = NULL;
dst->implied_opt_name = NULL;
QTAILQ_INIT(&dst->head);
dst->merge_lists = false;
}
if (need_head_update) {
QTAILQ_INIT(&dst->head);
}
dst->desc[num_dst_opts].name = NULL;
/* append list->desc to dst->desc */