On 02/07/2017 11:34 AM, Martin Kletzander wrote:
> On Fri, Jan 20, 2017 at 10:42:48AM +0100, Michal Privoznik wrote:
>> When working with symlinks it is fairly easy to get into a loop.
>> Don't.
>>
>> Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
>> ---
>> src/qemu/qemu_domain.c | 28 ++++++++++++++++++++++++----
>> 1 file changed, 24 insertions(+), 4 deletions(-)
>>
>> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
>> index 8cbfb2d16..448583313 100644
>> --- a/src/qemu/qemu_domain.c
>> +++ b/src/qemu/qemu_domain.c
>> @@ -6954,9 +6954,10 @@ qemuDomainGetPreservedMounts(virQEMUDriverPtr
>> driver,
>>
>>
>> static int
>> -qemuDomainCreateDevice(const char *device,
>> - const char *path,
>> - bool allow_noent)
>> +qemuDomainCreateDeviceRecursive(const char *device,
>> + const char *path,
>> + bool allow_noent,
>> + unsigned int ttl)
>> {
>> char *devicePath = NULL;
>> char *target = NULL;
>> @@ -6968,6 +6969,13 @@ qemuDomainCreateDevice(const char *device,
>> char *tcon = NULL;
>> #endif
>>
>> + if (!ttl) {
>> + virReportSystemError(ELOOP,
>> + _("Too many levels of symbolic links: %s"),
>> + device);
>> + return ret;
>> + }
>> +
>> if (lstat(device, &sb) < 0) {
>> if (errno == ENOENT && allow_noent) {
>> /* Ignore non-existent device. */
>> @@ -7057,7 +7065,8 @@ qemuDomainCreateDevice(const char *device,
>> tmp = NULL;
>> }
>>
>> - if (qemuDomainCreateDevice(target, path, allow_noent) < 0)
>> + if (qemuDomainCreateDeviceRecursive(target, path,
>> + allow_noent, ttl - 1) < 0)
>> goto cleanup;
>> } else {
>> if (create &&
>> @@ -7128,6 +7137,17 @@ qemuDomainCreateDevice(const char *device,
>> }
>>
>>
>> +static int
>> +qemuDomainCreateDevice(const char *device,
>> + const char *path,
>> + bool allow_noent)
>> +{
>> + long symloop_max = sysconf(_SC_SYMLOOP_MAX);
>> +
>> + return qemuDomainCreateDeviceRecursive(device, path,
>> + allow_noent, symloop_max);
>
> So you are taking 'long' that can, officially, be '-1' and pass it to a
> function as unsigned int. Having a maximum is nice, I have no idea why
> on my system there is no limit apparently (sysconf() returns -1 with no
> errno set), but if the system doesn't report any (like my case above) it
> effectively makes the SYMLOOP_MAX = UINT_MAX in this codepath. Should
> we avoid that or just let it be? This way it's still better than
> unlimited, so ACK to this version, but I just wanted a (short)
> discussion about this.
Sure. I think it's safe to assume if the level of symlinks reaches
UINT_MAX your system is terribly broken.
Michal
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