CVE-2025-39756

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

fs: Prevent file descriptor table allocations exceeding INT_MAX

When sysctl_nr_open is set to a very high value (for example, 1073741816

as set by systemd), processes attempting to use file descriptors near

the limit can trigger massive memory allocation attempts that exceed

INT_MAX, resulting in a WARNING in mm/slub.c:

WARNING: CPU: 0 PID: 44 at mm/slub.c:5027 __kvmalloc_node_noprof+0x21a/0x288

This happens because kvmalloc_array() and kvmalloc() check if the

requested size exceeds INT_MAX and emit a warning when the allocation is

not flagged with __GFP_NOWARN.

Specifically, when nr_open is set to 1073741816 (0x3ffffff8) and a

process calls dup2(oldfd, 1073741880), the kernel attempts to allocate:

- File descriptor array: 1073741880 * 8 bytes = 8,589,935,040 bytes

- Multiple bitmaps: ~400MB

- Total allocation size: > 8GB (exceeding INT_MAX = 2,147,483,647)

Reproducer:

1. Set /proc/sys/fs/nr_open to 1073741816:

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References