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5d85b8a8f4
Inspired by a simpler patch from "Wangrui (K) <moon.wangrui@huawei.com>". A submitted patch pointed out that virNetlinkCommand() was doing an improper typecast of the return value from nl_recv() (int to unsigned), causing it to miss error returns, and that even after remedying that problem, virNetlinkCommand() was calling VIR_FREE() on the pointer returned from nl_recv() (*resp) even if nl_recv() had returned an error, and that in this case the pointer was verifiably invalid, as it was pointing to memory that had been allocated by libnl, but then freed prior to returning the error. While reviewing this patch, I noticed several other problems with this seemingly simple function (at least one of them as serious as the problem being reported/fixed by the aforementioned patch), and decided they all deserved to be fixed. Here is the list: 1) The return value from nl_recv() must be assigned to an int (rather than unsigned int) in order to detect failure. 2) When nl_recv() returns an error or 0, the contents of *resp is invalid, and should be simply set to 0, *not* VIR_FREE()'d. 3) When nl_recv() returns 0, errno is not set, so the logged error message should not reference errno (it *is* an error though). 4) The first error return from virNetlinkCommand returns -EINVAL, incorrectly implying that the caller can expect the return value to be of the "-errno" variety, which is not true in any other case. 5) The 2nd error return returns directly with garbage in *resp. While the caller should never use *resp in this case, it's still good practice to set it to NULL. 6) For the next 5 (!!) error conditions, *resp will contain garbage, and virNetlinkCommand() will goto it's cleanup code which will VIR_FREE(*resp), almost surely leading to a segfault. In addition to fixing these 6 problems, this patch also makes the following two changes to make the function conform more closely to the style of other libvirt code: 1) Change the handling of return code from "named rc and defaulted to 0, but changed to -1 on error" to the more common "named ret and defaulted to -1, but changed to 0 on success". 2) Rename the "error" label to "cleanup", since the code that follows is executed in success cases as well as failure.
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>