UID and GID shifting for containers in user namespaces
A request to access an image stored by a host operating system (OS) maybe received from a process running in a container. The container may run a namespace including a plurality of namespace user identifiers (UIDs). A host UID corresponding to the namespace UID of the process may be synchronized with a host UID of an owner of the image based on configuration data of the namespace. In this way, multiple containers running namespaces may access a read only image file without requiring the image file to be copied for each container, thus preserving memory resources.
1. A method comprising:
receiving, from a process running in a container, a request to access an image file stored by a host operating system (OS), the container running a namespace including a plurality of namespace user identifiers (UIDs); and
synchronizing, by a processing device, a first host UID corresponding to a namespace UID of the process to a second host UID corresponding to an owner of the image file in view of configuration data of the namespace to present the second host UID to a kernel of the host OS as the first host UID.
2. The method of claim 1 , wherein the configuration data of the namespace includes a mapping from each of the plurality of namespace UIDs to a corresponding host UID.
3. The method of claim 2 , further comprising:
determining the first host UID in view of the configuration data of the namespace.
4. The method of claim 1 , wherein the synchronizing is performed at a run time of the container.
5. The method of claim 1 , wherein the synchronizing is performed using a storage driver in user space without host OS root user privileges.
6. The method of claim 1 , wherein:
memory for a plurality of containers to access the image is allocated once; and
one copy of the image is stored for access by the plurality of containers.
7. The method of claim 1 , wherein the namespace UID of the process corresponds to a namespace UID of a root user of the container.
8. A system comprising:
a memory to store an image file;
a processing device to:
receive, from a process running in a container, a request to access the image file stored by a host operating system (OS), the container running a namespace including a plurality of namespace user identifiers (UIDs); and
synchronize a first host UID corresponding to a namespace UID of the process to a second host UID corresponding to an owner of the image file in view of configuration data of the namespace to present the second host UID to a kernel of the host OS as the first host UID.
9. The system of claim 8 , wherein the configuration data of the namespace includes a mapping of each the plurality of namespace UIDs to a corresponding host UID.
10. The system of claim 9 , wherein the processing device is further to:
determine the first host UID in view of the configuration data of the namespace.
11. The system of claim 8 , wherein the processing device performs the synchronizing at a run time of the container.
12. The system of claim 8 , wherein the processing device performs the synchronizing using a storage driver in user space without host OS root user privileges.
13. The system of claim 8 , wherein the processing device is further to:
allocate memory for a plurality of containers to access the image once; and
store one copy of the image for access by the plurality of containers in the memory.
14. The system of claim 8 , wherein the namespace UID of the process corresponds to a namespace UID of a root user of the container.
15. A non-transitory computer-readable storage medium including instructions that, when executed by a processing device, cause the processing device to:
receive, from a process running in a container, a request to access an image file stored by a host operating system (OS), the container running a namespace including a plurality of namespace user identifiers (UIDs); and
synchronize a first host UID corresponding to a namespace UID of the process to a second host UID corresponding to an owner of the image file in view of configuration data of the namespace to present the second host UID to a kernel of the host OS as the first host UID.
16. The non-transitory computer-readable storage medium of claim 15 , wherein the configuration data of the namespace includes a mapping of each the plurality of namespace UIDs to a corresponding host UID.
17. The non-transitory computer-readable storage medium of claim 16 , wherein the processing device is further to:
determine the first host UID in view of the configuration data of the namespace.
18. The non-transitory computer-readable storage medium of claim 15 , wherein the processing device performs the synchronizing at a run time of the container.
19. The non-transitory computer-readable storage medium of claim 15 , wherein the processing device performs the synchronizing using a storage driver in user space without host OS root user privileges.
20. The non-transitory computer-readable storage medium of claim 15 , wherein the processing device is further to:
allocate memory for a plurality of containers to access the image once; and
store one copy of the image for access by the plurality of containers in the memory.