fs: drop peer group ids under namespace lock

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: fs: drop peer group ids under namespace lock When cleaning up peer group ids in the failure path we need to make sure to hold on to the namespace lock. Otherwise another thread might just turn the mount from a shared into a non-shared mount concurrently.

References

• https://git.kernel.org/stable/c/0af8fae81d8b7f1beddc17c5d4cfa43235134648
• https://git.kernel.org/stable/c/ddca03d97daa7b07b60c52e3d3060762732c6666
• https://git.kernel.org/stable/c/65c324d3f35c05e37afec39ac80743583fdcc96c
• https://git.kernel.org/stable/c/cb2239c198ad9fbd5aced22cf93e45562da781eb