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newgidmap: enforce setgroups=deny if self-mapping a group This is necessary to match the kernel-side policy of "self-mapping in a user namespace is fine, but you cannot drop groups" -- a policy that was created in order to stop user namespaces from allowing trivial privilege escalation by dropping supplementary groups that were "blacklisted" from certain paths. This is the simplest fix for the underlying issue, and effectively makes it so that unless a user has a valid mapping set in /etc/subgid (which only administrators can modify) -- and they are currently trying to use that mapping -- then /proc/$pid/setgroups will be set to deny. This workaround is only partial, because ideally it should be possible to set an "allow_setgroups" or "deny_setgroups" flag in /etc/subgid to allow administrators to further restrict newgidmap(1). We also don't write anything in the "allow" case because "allow" is the default, and users may have already written "deny" even if they technically are allowed to use setgroups. And we don't write anything if the setgroups policy is already "deny". Ref: https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/1729357 Fixes: CVE-2018-7169 Affects shadow <= 4.5 (From OE-Core rev: a875522540372a4fa6658885692e564dfd729f54) (From OE-Core rev: cfc8931d53cf9959995a4068a7e397e100922358) Signed-off-by: Jagadeesh Krishnanjanappa <jkrishnanjanappa@mvista.com> Signed-off-by: Armin Kuster <akuster808@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org> Signed-off-by: Armin Kuster <akuster808@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
QEMU Emulation Targets ====================== To simplify development, the build system supports building images to work with the QEMU emulator in system emulation mode. Several architectures are currently supported in 32 and 64 bit variants: * ARM (qemuarm + qemuarm64) * x86 (qemux86 + qemux86-64) * PowerPC (qemuppc only) * MIPS (qemumips + qemumips64) Use of the QEMU images is covered in the Yocto Project Reference Manual. The appropriate MACHINE variable value corresponding to the target is given in brackets.