[PATCH bpf] bpf: fix bug in mmap() implementation for BPF array map

[Andrii Nakryiko]

mmap() subsystem allows user-space application to memory-map region with
initial page offset. This wasn't taken into account in initial implementation
of BPF array memory-mapping. This would result in wrong pages, not taking into
account requested page shift, being memory-mmaped into user-space. This patch
fixes this gap and adds a test for such scenario.

Fixes: fc9702273e2e ("bpf: Add mmap() support for BPF_MAP_TYPE_ARRAY")
Signed-off-by: Andrii Nakryiko <andr...@fb.com>
---
 kernel/bpf/arraymap.c                         | 7 ++++++-
 tools/testing/selftests/bpf/prog_tests/mmap.c | 8 ++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 95d77770353c..1d6120fd5ba6 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -486,7 +486,12 @@ static int array_map_mmap(struct bpf_map *map, struct 
vm_area_struct *vma)
        if (!(map->map_flags & BPF_F_MMAPABLE))
                return -EINVAL;
 
-       return remap_vmalloc_range(vma, array_map_vmalloc_addr(array), pgoff);
+       if (vma->vm_pgoff * PAGE_SIZE + (vma->vm_end - vma->vm_start) >
+           PAGE_ALIGN((u64)array->map.max_entries * array->elem_size))
+               return -EINVAL;
+
+       return remap_vmalloc_range(vma, array_map_vmalloc_addr(array),
+                                  vma->vm_pgoff + pgoff);
 }
 
 const struct bpf_map_ops array_map_ops = {
diff --git a/tools/testing/selftests/bpf/prog_tests/mmap.c 
b/tools/testing/selftests/bpf/prog_tests/mmap.c
index 56d80adcf4bd..6b9dce431d41 100644
--- a/tools/testing/selftests/bpf/prog_tests/mmap.c
+++ b/tools/testing/selftests/bpf/prog_tests/mmap.c
@@ -217,6 +217,14 @@ void test_mmap(void)
 
        munmap(tmp2, 4 * page_size);
 
+       /* map all 4 pages, but with pg_off=1 page, should fail */
+       tmp1 = mmap(NULL, 4 * page_size, PROT_READ, MAP_SHARED | MAP_FIXED,
+                   data_map_fd, page_size /* initial page shift */);
+       if (CHECK(tmp1 != MAP_FAILED, "adv_mmap7", "unexpected success")) {
+               munmap(tmp1, 4 * page_size);
+               goto cleanup;
+       }
+
        tmp1 = mmap(NULL, map_sz, PROT_READ, MAP_SHARED, data_map_fd, 0);
        if (CHECK(tmp1 == MAP_FAILED, "last_mmap", "failed %d\n", errno))
                goto cleanup;
-- 
2.24.1