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Re: [libvirt] [PATCHv2 13/15] util: virSetUIDGIDWithCaps - change uid while keeping caps

On 02/12/2013 01:15 PM, Laine Stump wrote:
> Normally when a process' uid is changed to non-0, all the capabilities
> bits are cleared, even those explicitly set with calls to
> capng_update()/capng_apply() made immediately before setuid. And
> *after* the process' uid has been changed, it no longer has the
> necessary privileges to add capabilities back to the process.

> Because the modification/maintaining of capabilities is intermingled
> with setting the uid, this is necessarily done in a single function,
> rather than having two independent functions.
> Note that, due to the way that effective capabilities are computed (at
> time of execve) for a process that has uid != 0, the *file*
> capabilities of the binary being executed must also have the desired
> capabilities bit(s) set (see "man 7 capabilities"). This can be done
> with the "filecap" command. (e.g. "filecap /usr/bin/qemu-kvm sys_rawio").
> ---
> Change from V1:
> * properly cast when comparing gid/uid, and only short circuit for -1 (not 0)
> * fix // style comments
> * add ATTRIBUTE_UNUSED where appropriate for capBits argument.

ACK with nits fixed:

> @@ -2990,6 +2991,116 @@ virGetGroupName(gid_t gid ATTRIBUTE_UNUSED)
>  }
>  #endif /* HAVE_GETPWUID_R */
> +/* Set the real and effective uid and gid to the given values, while
> + * maintaining the capabilities indicated by bits in @capBits. return


Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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