[PATCH bpf v4 1/2] bpf: Fix OOB in pcpu_init_value

[xulang]

From: Lang Xu <xulang@xxxxxxxxxxxxx>

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@xxxxxxxxxxx>
Closes: https://lore.kernel.org/all/14e6c70c.6c121.19c0399d948.Coremail.kaiyanm@xxxxxxxxxxx/
Signed-off-by: Lang Xu <xulang@xxxxxxxxxxxxx>
---
 kernel/bpf/hashtab.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index bc6bc8bb871d..fb8123cfa5ec 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1056,7 +1056,7 @@ static void pcpu_init_value(struct bpf_htab *htab, void __percpu *pptr,
 
 		for_each_possible_cpu(cpu) {
 			if (cpu == current_cpu)
-				copy_map_value_long(&htab->map, per_cpu_ptr(pptr, cpu), value);
+				copy_map_value(&htab->map, per_cpu_ptr(pptr, cpu), value);
 			else /* Since elem is preallocated, we cannot touch special fields */
 				zero_map_value(&htab->map, per_cpu_ptr(pptr, cpu));
 		}
-- 
2.51.0