block: fix potential invalid pointer dereference in blk_add_partition

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: block: fix potential invalid pointer dereference in blk_add_partition The blk_add_partition() function initially used a single if-condition (IS_ERR(part)) to check for errors when adding a partition. This was modified to handle the specific case of -ENXIO separately, allowing the function to proceed without logging the error in this case. However, this change unintentionally left a path where md_autodetect_dev() could be called without confirming that part is a valid pointer. This commit separates the error handling logic by splitting the initial if-condition, improving code readability and handling specific error scenarios explicitly. The function now distinguishes the general error case from -ENXIO without altering the existing behavior of md_autodetect_dev() calls.

References

• https://git.kernel.org/stable/c/4bc4272e2506941c3f3d4fb8b0c659ee814dcf6f
• https://git.kernel.org/stable/c/cc4d21d9492db4e534d3e01253cf885c90dd2a8b
• https://git.kernel.org/stable/c/64cf2a39202ca2d9df5ee70eb310b6141ce2b8ed
• https://git.kernel.org/stable/c/80f5bfbb80ea1615290dbc24f49d3d8c86db58fe
• https://git.kernel.org/stable/c/652039ba477c9a4ab43740cf2cb0d068d53508c2
• https://git.kernel.org/stable/c/afe53ea9b378c376101d99d216f13b6256f75189
• https://git.kernel.org/stable/c/26e197b7f9240a4ac301dd0ad520c0c697c2ea7d