linux-kernel - [PATCH] fs: afs: Fix a possible null-pointer dereference in afs_put

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Message-Id: <20190723122553.14565-1-baijiaju1990@gmail.com>
Date:   Tue, 23 Jul 2019 20:25:53 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     dhowells@...hat.com
Cc:     linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] fs: afs: Fix a possible null-pointer dereference in afs_put_read()

In afs_read_dir(), there is an if statement on line 255 to check whether
req->pages is NULL:
	if (!req->pages)
		goto error;

If req->pages is NULL, afs_put_read() on line 337 is executed.
In afs_put_read(), req->pages[i] is used on line 195.
Thus, a possible null-pointer dereference may occur in this case.

To fix this possible bug, an if statement is added in afs_put_read() to
check req->pages.

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 fs/afs/file.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 56b69576274d..dd3c55c9101c 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -191,11 +191,13 @@ void afs_put_read(struct afs_read *req)
 	int i;
 
 	if (refcount_dec_and_test(&req->usage)) {
-		for (i = 0; i < req->nr_pages; i++)
-			if (req->pages[i])
-				put_page(req->pages[i]);
-		if (req->pages != req->array)
-			kfree(req->pages);
+		if (req->pages) {
+			for (i = 0; i < req->nr_pages; i++)
+				if (req->pages[i])
+					put_page(req->pages[i]);
+			if (req->pages != req->array)
+				kfree(req->pages);
+		}
 		kfree(req);
 	}
 }
-- 
2.17.0