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Subject[PATCH v3 3/4] f2fs: fix NULL pointer dereference in f2fs_verity_work()
Date
If both compression and fsverity feature is on, generic/572 will
report below NULL pointer dereference bug.

BUG: kernel NULL pointer dereference, address: 0000000000000018
RIP: 0010:f2fs_verity_work+0x60/0x90 [f2fs]
#PF: supervisor read access in kernel mode
Workqueue: fsverity_read_queue f2fs_verity_work [f2fs]
RIP: 0010:f2fs_verity_work+0x60/0x90 [f2fs]
Call Trace:
process_one_work+0x16c/0x3f0
worker_thread+0x4c/0x440
? rescuer_thread+0x350/0x350
kthread+0xf8/0x130
? kthread_unpark+0x70/0x70
ret_from_fork+0x35/0x40

There are two issue in f2fs_verity_work():
- it needs to traverse and verify all pages in bio.
- if pages in bio belong to non-compressed cluster, accessing
decompress IO context stored in page private will cause NULL
pointer dereference.

Fix them.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
v3:
- call f2fs_verify_pages() when checking last compress page
to avoid NULL pointer dereference.
fs/f2fs/compress.c | 2 ++
fs/f2fs/data.c | 35 ++++++++++++++++++++++++++++++-----
2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 00fd6f904139..748ed8ad1d5a 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -477,6 +477,8 @@ void f2fs_decompress_pages(struct bio *bio, struct page *page, bool verity)
out_vunmap_rbuf:
vunmap(dic->rbuf);
out_free_dic:
+ if (verity)
+ refcount_add(dic->nr_cpages - 1, &dic->ref);
if (!verity)
f2fs_decompress_end_io(dic->rpages, dic->cluster_size,
ret, false);
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index bb66faf09eea..0197b7b80d19 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -187,12 +187,37 @@ static void f2fs_verify_pages(struct page **rpages, unsigned int cluster_size)

static void f2fs_verify_bio(struct bio *bio)
{
- struct page *page = bio_first_page_all(bio);
- struct decompress_io_ctx *dic =
- (struct decompress_io_ctx *)page_private(page);
+ struct bio_vec *bv;
+ struct bvec_iter_all iter_all;
+
+ bio_for_each_segment_all(bv, bio, iter_all) {
+ struct page *page = bv->bv_page;
+ struct decompress_io_ctx *dic;
+
+ dic = (struct decompress_io_ctx *)page_private(page);
+
+ if (dic) {
+ if (refcount_dec_not_one(&dic->ref))
+ continue;
+ f2fs_verify_pages(dic->rpages,
+ dic->cluster_size);
+ f2fs_free_dic(dic);
+ continue;
+ }
+
+ if (bio->bi_status || PageError(page))
+ goto clear_uptodate;

- f2fs_verify_pages(dic->rpages, dic->cluster_size);
- f2fs_free_dic(dic);
+ if (fsverity_verify_page(page)) {
+ SetPageUptodate(page);
+ goto unlock;
+ }
+clear_uptodate:
+ ClearPageUptodate(page);
+ ClearPageError(page);
+unlock:
+ unlock_page(page);
+ }
}
#endif

--
2.18.0.rc1
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