bpf: Fix bug in mmap() implementation for BPF array map

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: fc97022 ("bpf: Add mmap() support for BPF_MAP_TYPE_ARRAY") Signed-off-by: Andrii Nakryiko <[email protected]> Signed-off-by: Alexei Starovoitov <[email protected]> Acked-by: Yonghong Song <[email protected]> Link: https://lore.kernel.org/bpf/[email protected]
ambv · May 14, 2020 · 333291c · 333291c
1 parent 23ad046
commit 333291c
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Showing 2 changed files with 14 additions and 1 deletion.
diff --git 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
@@ -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;