linux-kernel - [PATCH v2 3/5] f2fs: fix to avoid NULL pointer dereference

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Date:   Wed, 25 Mar 2020 17:18:11 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>,
        Chao Yu <yuchao0@...wei.com>
Subject: [PATCH v2 3/5] f2fs: fix to avoid NULL pointer dereference

Unable to handle kernel NULL pointer dereference at virtual address 00000000
PC is at f2fs_free_dic+0x60/0x2c8
LR is at f2fs_decompress_pages+0x3c4/0x3e8
f2fs_free_dic+0x60/0x2c8
f2fs_decompress_pages+0x3c4/0x3e8
__read_end_io+0x78/0x19c
f2fs_post_read_work+0x6c/0x94
process_one_work+0x210/0x48c
worker_thread+0x2e8/0x44c
kthread+0x110/0x120
ret_from_fork+0x10/0x18

In f2fs_free_dic(), we can not use f2fs_put_page(,1) to release dic->tpages[i],
as the page's mapping is NULL.

Signed-off-by: Chao Yu <yuchao0@...wei.com>
---
v2:
- fix to skip release tpages[i] if it is NULL in error path.
 fs/f2fs/compress.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index ef7dd04312fe..6e10800729b6 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1137,7 +1137,10 @@ void f2fs_free_dic(struct decompress_io_ctx *dic)
 		for (i = 0; i < dic->cluster_size; i++) {
 			if (dic->rpages[i])
 				continue;
-			f2fs_put_page(dic->tpages[i], 1);
+			if (!dic->tpages[i])
+				continue;
+			unlock_page(dic->tpages[i]);
+			put_page(dic->tpages[i]);
 		}
 		kfree(dic->tpages);
 	}
-- 
2.18.0.rc1