CVE-2025-37807

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

bpf: Fix kmemleak warning for percpu hashmap

Vlad Poenaru reported the following kmemleak issue:

unreferenced object 0x606fd7c44ac8 (size 32):

backtrace (crc 0):

pcpu_alloc_noprof+0x730/0xeb0

bpf_map_alloc_percpu+0x69/0xc0

prealloc_init+0x9d/0x1b0

htab_map_alloc+0x363/0x510

map_create+0x215/0x3a0

__sys_bpf+0x16b/0x3e0

__x64_sys_bpf+0x18/0x20

do_syscall_64+0x7b/0x150

entry_SYSCALL_64_after_hwframe+0x4b/0x53

Further investigation shows the reason is due to not 8-byte aligned

store of percpu pointer in htab_elem_set_ptr():

*(void __percpu **)(l->key + key_size) = pptr;

Note that the whole htab_elem alignment is 8 (for x86_64). If the key_size

is 4, that means pptr is stored in a location which is 4 byte aligned but

not 8 byte aligned. In mm/kmemleak.c, scan_block() scans the memory based

on 8 byte stride, so it won't detect above pptr, hence reporting the memory

leak.

In htab_map_alloc(), we already have

htab->elem_size = sizeof(struct htab_elem) +

round_up(htab->map.key_size, 8);

if (percpu)

htab->elem_size += sizeof(void *);

else

htab->elem_size += round_up(htab->map.value_size, 8);

So storing pptr with 8-byte alignment won't cause any problem and can fix

kmemleak too.

The issue can be reproduced with bpf selftest as well:

1. Enable CONFIG_DEBUG_KMEMLEAK config

2. Add a getchar() before skel destroy in test_hash_map() in prog_tests/for_each.c.

The purpose is to keep map available so kmemleak can be detected.

3. run './test_progs -t for_each/hash_map &' and a kmemleak should be reported.