linux: add some check for NULL pointers before accessing them

[giuseppe]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @giuseppe, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on enhancing the stability and robustness of the libcrun library by introducing several NULL pointer checks across various functions within src/libcrun/linux.c. These checks specifically target the linux configuration object and its related data structures, ensuring that they are valid before being accessed. This prevents potential segmentation faults and improves the overall reliability of the container runtime.

Highlights

• NULL Pointer Checks in create_missing_devs: Added a check to ensure def->linux is not NULL before proceeding with operations in the create_missing_devs function, preventing potential crashes.
• NULL Pointer Checks in do_masked_and_readonly_paths: Implemented a NULL check for def->linux at the beginning of the do_masked_and_readonly_paths function to safeguard against dereferencing a NULL pointer.
• Improved NULL Safety for rootfs_propagation: Modified the condition in libcrun_set_mounts to explicitly check for a non-NULL def->linux before accessing its rootfs_propagation member.
• NULL Pointer Checks in libcrun_set_usernamespace: Introduced a NULL check for def->linux in libcrun_set_usernamespace to ensure that subsequent accesses to its members are safe.
• Enhanced NULL Checks in get_id_in_user_namespace: Added comprehensive NULL checks for def->linux and the mappings arrays (uid/gid) within get_id_in_user_namespace to prevent invalid memory access and improve robustness.

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[gemini-code-assist]

Code Review

This pull request adds several necessary NULL checks for the def->linux pointer before it is dereferenced, which prevents potential crashes. This is a good improvement. However, in several places, the def pointer itself is not checked for NULL before being used to access linux. If def can be NULL, this would still lead to a segmentation fault. I've pointed out these locations and suggested adding checks for def as well. I also found a minor opportunity to simplify one of the new checks by removing a redundant condition.

[gemini-code-assist]

The def pointer, which is likely initialized from container->container_def, is dereferenced without a NULL check. If def is NULL, this will cause a segmentation fault. Please add a NULL check for def as well.

  if (!def || !def->linux)
    return 0;

[gemini-code-assist]

The def pointer is dereferenced without being checked for NULL. If container->container_def is NULL, this will lead to a segmentation fault. You should add a NULL check for def.

  if (!def || !def->linux)
    return 0;

[gemini-code-assist]

The def pointer, initialized from container->container_def, is dereferenced without a NULL check. This could lead to a segmentation fault if container->container_def is NULL. Please add a check for def.

  if (!def || !def->linux)
    return 0;

[gemini-code-assist]

The def pointer, passed as an argument, could be NULL. Dereferencing it to check def->linux would cause a segmentation fault. You should check def for NULL first.

  if (!def || !def->linux)
    goto exit;

[gemini-code-assist]

The len == 0 check is redundant. The following for loop's condition (i < len) already handles the case where len is 0 by not executing the loop body. Removing this redundant check simplifies the code.

  if (!mappings)
    goto exit;

[packit-as-a-service]

TMT tests failed. @containers/packit-build please check.

[giuseppe]

/gemini review

[gemini-code-assist]

Code Review

This pull request adds several NULL pointer checks before accessing members of the def and def->linux structs. These changes improve the robustness of the code by preventing potential segmentation faults. The added checks in create_missing_devs, do_masked_and_readonly_paths, libcrun_set_mounts, libcrun_set_usernamespace, and get_id_in_user_namespace are correct and necessary. I have one suggestion for a minor code simplification.

[gemini-code-assist]

The check for len == 0 is redundant. If len is 0, the subsequent for loop for (i = 0; i < len; i++) will not execute its body, and the function will proceed to the exit: label, which has the same effect as goto exit;. You can simplify the condition to only check if mappings is NULL.

  if (! mappings)
    goto exit;