block: fix memory leak in __blkdev_issue_zero_pages

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: block: fix memory leak in __blkdev_issue_zero_pages Move the fatal signal check before bio_alloc() to prevent a memory leak when BLKDEV_ZERO_KILLABLE is set and a fatal signal is pending. Previously, the bio was allocated before checking for a fatal signal. If a signal was pending, the code would break out of the loop without freeing or chaining the just-allocated bio, causing a memory leak. This matches the pattern already used in __blkdev_issue_write_zeroes() where the signal check precedes the allocation.

References

• https://git.kernel.org/stable/c/453e4b0c84d0db1454ff0adf655d91179e6fca3a
• https://git.kernel.org/stable/c/7957635c679e8a01147163a3a4a1f16e1210fa03
• https://git.kernel.org/stable/c/7193407bc4457212fa38ec3aff9c640e63a8dbef
• https://git.kernel.org/stable/c/f7e3f852a42d7cd8f1af2c330d9d153e30c8adcf