f2fs: compress: fix to avoid use-after-free on dic

Call trace:
 __memcpy+0x128/0x250
 f2fs_read_multi_pages+0x940/0xf7c
 f2fs_mpage_readpages+0x5a8/0x624
 f2fs_readahead+0x5c/0x110
 page_cache_ra_unbounded+0x1b8/0x590
 do_sync_mmap_readahead+0x1dc/0x2e4
 filemap_fault+0x254/0xa8c
 f2fs_filemap_fault+0x2c/0x104
 __do_fault+0x7c/0x238
 do_handle_mm_fault+0x11bc/0x2d14
 do_mem_abort+0x3a8/0x1004
 el0_da+0x3c/0xa0
 el0t_64_sync_handler+0xc4/0xec
 el0t_64_sync+0x1b4/0x1b8

In f2fs_read_multi_pages(), once f2fs_decompress_cluster() was called if
we hit cached page in compress_inode's cache, dic may be released, it needs
break the loop rather than continuing it, in order to avoid accessing
invalid dic pointer.

Fixes: 6ce19af ("f2fs: compress: add compress_inode to cache compressed blocks")
Signed-off-by: Chao Yu <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>

Author: chaseyu

fs/f2fs/data.c

@@ -2344,8 +2344,10 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
 		f2fs_wait_on_block_writeback(inode, blkaddr);
 
 		if (f2fs_load_compressed_page(sbi, page, blkaddr)) {
-			if (atomic_dec_and_test(&dic->remaining_pages))
+			if (atomic_dec_and_test(&dic->remaining_pages)) {
 				f2fs_decompress_cluster(dic, true);
+				break;
+			}
 			continue;
 		}