CVE-2026-98588: bpf, sockmap: Reject max_entries > INT_MAX in sock_map_alloc

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

bpf, sockmap: Reject maxentries > INTMAX in sockmapalloc

sockmapalloc() only rejects maxentries == 0 and otherwise allows any u32 value. sockmapfree() then walks the sks[] array with a signed int iterator:

int i; for (i = 0; i < stab->map.maxentries; i++) struct sock psk = &stab->sks[i];

When a SOCKMAP is created with maxentries = 0xffffffff (UINTMAX), the allocation of 32 GiB can succeed on large-memory hosts. During free the counter reaches 0x80000000, wraps to INTMIN, is sign-extended by movslq and turned into a ~16 GiB negative offset from stab->sks, pointing far below the allocation.

The faulting access is an xchg() write in sockmapfree(). Without KASAN, the same out-of-bounds write can fault on an unmapped vmalloc page or corrupt an unrelated allocation if that vmalloc address is populated. On a KASAN kernel with CONFIGKASANVMALLOC=y, the shadow check for that address hits an unmapped shadow page and oopses first:

BUG: unable to handle page fault for address: fffff521b59c5a00 RIP: 0010:kasancheckrange+0x107/0x190 Call Trace: sockmapfree+0x93/0x190 mapcreate+0x68d/0xb30 sysbpf+0x21e/0x2e70

Vmcore confirmed stab->map.maxentries == 0xffffffff, stab->sks == 0xffffc911ace2d000, and the faulting address sks + (s64)INTMIN 8 exactly at 0xffffc90dace2d000. The same buggy path is reached on the normal close()/bpfmapfreedeferred() path whenever such a map is destroyed.

sockmapalloc() used to bound its allocation size through bpfmapchargeinit(), but the bound was dropped when rlimit-based memory accounting was removed. Reject maxentries > INTMAX at creation time so the signed iterator in sockmapfree() never sees a value that would overflow.

Triggered by syzkaller and reproduced on both a 6.6-based KASAN kernel and the upstream v7.3-rc2 kernel.