[PATCH 5.10/5.15] bpf: Fix OOB in pcpu_init_value

[Mikhail Dmitrichenko <mdmitrichenko@astralinux.ru>]

From: Lang Xu <xulang@uniontech.com>

commit 576afddfee8d1108ee299bf10f581593540d1a36 upstream.

An out-of-bounds read occurs when copying element from a
BPF_MAP_TYPE_CGROUP_STORAGE map to another pcpu map with the
same value_size that is not rounded up to 8 bytes.

The issue happens when:
1. A CGROUP_STORAGE map is created with value_size not aligned to
   8 bytes (e.g., 4 bytes)
2. A pcpu map is created with the same value_size (e.g., 4 bytes)
3. Update element in 2 with data in 1

pcpu_init_value assumes that all sources are rounded up to 8 bytes,
and invokes copy_map_value_long to make a data copy, However, the
assumption doesn't stand since there are some cases where the source
may not be rounded up to 8 bytes, e.g., CGROUP_STORAGE, skb->data.
the verifier verifies exactly the size that the source claims, not
the size rounded up to 8 bytes by kernel, an OOB happens when the
source has only 4 bytes while the copy size(4) is rounded up to 8.

Fixes: d3bec0138bfb ("bpf: Zero-fill re-used per-cpu map element")
Reported-by: Kaiyan Mei <kaiyanm@hust.edu.cn>
Closes: https://lore.kernel.org/all/14e6c70c.6c121.19c0399d948.Coremail.kaiyanm@hust.edu.cn/
Link: https://lore.kernel.org/r/420FEEDDC768A4BE+20260402074236.2187154-1-xulang@uniontech.com
Signed-off-by: Lang Xu <xulang@uniontech.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
[mdmitrichenko: The older implementation uses bpf_long_memcpy()
 rather than copy_map_value_long(). Replace it with memcpy() using
 map.value_size to avoid reading beyond the source buffer.]
Signed-off-by: Mikhail Dmitrichenko <mdmitrichenko@astralinux.ru>
---
Backport fix for CVE-2026-53076.

 kernel/bpf/hashtab.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 4c7cab79d90e5..59f1ffa9a59d3 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -844,8 +844,8 @@ static void pcpu_init_value(struct bpf_htab *htab, void __percpu *pptr,
 
 		for_each_possible_cpu(cpu) {
 			if (cpu == current_cpu)
-				bpf_long_memcpy(per_cpu_ptr(pptr, cpu), value,
-						size);
+				memcpy(per_cpu_ptr(pptr, cpu), value,
+				       htab->map.value_size);
 			else
 				memset(per_cpu_ptr(pptr, cpu), 0, size);
 		}
-- 
2.43.0