[libvirt] [PATCH] virStorageTranslateDiskSourcePool: Avoid double free

[John Ferlan]

On 06/28/2016 09:02 AM, Michal Privoznik wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1316370
> 
> Consider the following disk for a domain:
> 
>     <disk type='volume' device='cdrom'>
>       <driver name='qemu' type='raw'/>
>       <auth username='libvirt'>
>         <secret type='iscsi' usage='libvirtiscsi'/>
>       </auth>
>       <source pool='iscsi-secret-pool' volume='unit:0:0:0' mode='direct' startupPolicy='optional'/>
>       <target dev='sda' bus='scsi'/>
>       <readonly/>
>       <address type='drive' controller='0' bus='0' target='0' unit='0'/>
>     </disk>
> 
> Now, startupPolicy is currently not allowed for iscsi disks, so
> one would expect an error message to be thrown. But what a
> surprise is waiting for users if they try to start up such
> domain:
> 
> ==15724== Invalid free() / delete / delete[] / realloc()
> ==15724==    at 0x4C2B1F0: free (vg_replace_malloc.c:473)
> ==15724==    by 0x54B7A69: virFree (viralloc.c:582)
> ==15724==    by 0x552DC90: virStorageAuthDefFree (virstoragefile.c:1549)
> ==15724==    by 0x552F023: virStorageSourceClear (virstoragefile.c:2055)
> ==15724==    by 0x552F054: virStorageSourceFree (virstoragefile.c:2067)
> ==15724==    by 0x55556AA: virDomainDiskDefFree (domain_conf.c:1562)
> ==15724==    by 0x5557ABE: virDomainDefFree (domain_conf.c:2547)
> ==15724==    by 0x1B43CC42: qemuProcessStop (qemu_process.c:5918)
> ==15724==    by 0x1B43BA2E: qemuProcessStart (qemu_process.c:5511)
> ==15724==    by 0x1B48993E: qemuDomainObjStart (qemu_driver.c:7050)
> ==15724==    by 0x1B489B9A: qemuDomainCreateWithFlags (qemu_driver.c:7104)
> ==15724==    by 0x1B489C01: qemuDomainCreate (qemu_driver.c:7122)
> ==15724==  Address 0x21cfbb90 is 0 bytes inside a block of size 48 free'd
> ==15724==    at 0x4C2B1F0: free (vg_replace_malloc.c:473)
> ==15724==    by 0x54B7A69: virFree (viralloc.c:582)
> ==15724==    by 0x552DC90: virStorageAuthDefFree (virstoragefile.c:1549)
> ==15724==    by 0x12D1C8D4: virStorageTranslateDiskSourcePool (storage_driver.c:3475)
> ==15724==    by 0x1B4396E4: qemuProcessPrepareDomain (qemu_process.c:4896)
> ==15724==    by 0x1B43B880: qemuProcessStart (qemu_process.c:5466)
> ==15724==    by 0x1B48993E: qemuDomainObjStart (qemu_driver.c:7050)
> ==15724==    by 0x1B489B9A: qemuDomainCreateWithFlags (qemu_driver.c:7104)
> ==15724==    by 0x1B489C01: qemuDomainCreate (qemu_driver.c:7122)
> ==15724==    by 0x561CA97: virDomainCreate (libvirt-domain.c:6787)
> ==15724==    by 0x12B6FD: remoteDispatchDomainCreate (remote_dispatch.h:4116)
> ==15724==    by 0x12B61A: remoteDispatchDomainCreateHelper (remote_dispatch.h:4092)
> 
> The problem is, in virStorageTranslateDiskSourcePool disk
> def->src->auth is freed, but the pointer is not set to NULL. So
> later, when qemuProcessStop starts to free the domain definition,
> virStorageAuthDefFree() tries to free the memory again, instead
> of jumping out immediately.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  src/storage/storage_driver.c | 3 +++
>  1 file changed, 3 insertions(+)
> 

Interesting... Looked at the bz, it wasn't clear from the description,
but it seems that the source pool (iscsi-secret-pool) didn't have the
'<auth>'; otherwise,  virStorageTranslateDiskSourcePoolAuth would have
filled in the auth details.

Wonder if virStorageSourceClear should also be adjusted so that it too
isn't bitten by the Free routines and pass by value not reference.


ACK for this (and I believe safe)

John
> diff --git a/src/storage/storage_driver.c b/src/storage/storage_driver.c
> index 831e6b0..cb9d578 100644
> --- a/src/storage/storage_driver.c
> +++ b/src/storage/storage_driver.c
> @@ -3472,7 +3472,10 @@ virStorageTranslateDiskSourcePool(virConnectPtr conn,
>  
>      VIR_FREE(def->src->path);
>      virStorageNetHostDefFree(def->src->nhosts, def->src->hosts);
> +    def->src->nhosts = 0;
> +    def->src->hosts = NULL;
>      virStorageAuthDefFree(def->src->auth);
> +    def->src->auth = NULL;
>  
>      switch ((virStoragePoolType) pooldef->type) {
>      case VIR_STORAGE_POOL_DIR:
>