CVE-2025-39756: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability has been identified in the Linux kernel (CVE-2025-39756) related to file descriptor table allocations. The issue was discovered and reported on September 11, 2025, affecting systems where sysctlnropen is set to very high values. When processes attempt to use file descriptors near the limit, they can trigger massive memory allocation attempts that exceed INT_MAX (NVD).

The vulnerability occurs when sysctlnropen is set to a high value (e.g., 1073741816) and processes attempt to use file descriptors near this limit. The kernel attempts to allocate memory for the file descriptor array (1073741880 * 8 bytes = 8,589,935,040 bytes) plus additional bitmaps (~400MB), resulting in a total allocation size exceeding 8GB and INTMAX (2,147,483,647). This triggers a WARNING in mm/slub.c due to kvmallocarray() and kvmalloc() checks (NVD).

When exploited, this vulnerability can cause the kernel to attempt impractical memory allocations exceeding 8GB, which will always fail. This can lead to system warnings and potential resource exhaustion, particularly affecting programs and tests that legitimately test file descriptor limits (NVD).

The fix involves adding a check in allocfdtable() to ensure the requested allocation size does not exceed INTMAX. This causes the operation to fail with -EMFILE instead of triggering a kernel warning, preventing the impractical memory allocation request (NVD).