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authorAndrii Nakryiko <andrii@kernel.org>2021-05-04 16:38:00 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2021-05-11 13:31:10 +0200
commit04ea3086c4d73da7009de1e84962a904139af219 (patch)
treefa1319ec2102abc1141abccb4a28e73c231db8d4 /kernel/bpf
parent4b81ccebaeee885ab1aa1438133f2991e3a2b6ea (diff)
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bpf: Prevent writable memory-mapping of read-only ringbuf pages
Only the very first page of BPF ringbuf that contains consumer position counter is supposed to be mapped as writeable by user-space. Producer position is read-only and can be modified only by the kernel code. BPF ringbuf data pages are read-only as well and are not meant to be modified by user-code to maintain integrity of per-record headers. This patch allows to map only consumer position page as writeable and everything else is restricted to be read-only. remap_vmalloc_range() internally adds VM_DONTEXPAND, so all the established memory mappings can't be extended, which prevents any future violations through mremap()'ing. Fixes: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it") Reported-by: Ryota Shiga (Flatt Security) Reported-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf')
-rw-r--r--kernel/bpf/ringbuf.c21
1 files changed, 8 insertions, 13 deletions
diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index b86d80c9cd59..84b3b35fc0d0 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -221,25 +221,20 @@ static int ringbuf_map_get_next_key(struct bpf_map *map, void *key,
return -ENOTSUPP;
}
-static size_t bpf_ringbuf_mmap_page_cnt(const struct bpf_ringbuf *rb)
-{
- size_t data_pages = (rb->mask + 1) >> PAGE_SHIFT;
-
- /* consumer page + producer page + 2 x data pages */
- return RINGBUF_POS_PAGES + 2 * data_pages;
-}
-
static int ringbuf_map_mmap(struct bpf_map *map, struct vm_area_struct *vma)
{
struct bpf_ringbuf_map *rb_map;
- size_t mmap_sz;
rb_map = container_of(map, struct bpf_ringbuf_map, map);
- mmap_sz = bpf_ringbuf_mmap_page_cnt(rb_map->rb) << PAGE_SHIFT;
-
- if (vma->vm_pgoff * PAGE_SIZE + (vma->vm_end - vma->vm_start) > mmap_sz)
- return -EINVAL;
+ if (vma->vm_flags & VM_WRITE) {
+ /* allow writable mapping for the consumer_pos only */
+ if (vma->vm_pgoff != 0 || vma->vm_end - vma->vm_start != PAGE_SIZE)
+ return -EPERM;
+ } else {
+ vma->vm_flags &= ~VM_MAYWRITE;
+ }
+ /* remap_vmalloc_range() checks size and offset constraints */
return remap_vmalloc_range(vma, rb_map->rb,
vma->vm_pgoff + RINGBUF_PGOFF);
}