linux-kernel - [PATCH AUTOSEL 6.2 09/18] fs/ntfs3: Fix a possible null-pointer dereference in ni

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Date:   Tue,  9 May 2023 17:19:47 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jia-Ju Bai <baijiaju1990@...il.com>,
        TOTE Robot <oslab@...nghua.edu.cn>,
        Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
        Sasha Levin <sashal@...nel.org>, ntfs3@...ts.linux.dev
Subject: [PATCH AUTOSEL 6.2 09/18] fs/ntfs3: Fix a possible null-pointer dereference in ni_clear()

From: Jia-Ju Bai <baijiaju1990@...il.com>

[ Upstream commit ec275bf9693d19cc0fdce8436f4c425ced86f6e7 ]

In a previous commit c1006bd13146, ni->mi.mrec in ni_write_inode()
could be NULL, and thus a NULL check is added for this variable.

However, in the same call stack, ni->mi.mrec can be also dereferenced
in ni_clear():

ntfs_evict_inode(inode)
  ni_write_inode(inode, ...)
    ni = ntfs_i(inode);
    is_rec_inuse(ni->mi.mrec) -> Add a NULL check by previous commit
  ni_clear(ntfs_i(inode))
    is_rec_inuse(ni->mi.mrec) -> No check

Thus, a possible null-pointer dereference may exist in ni_clear().
To fix it, a NULL check is added in this function.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
Reported-by: TOTE Robot <oslab@...nghua.edu.cn>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@...agon-software.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/ntfs3/frecord.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
index 912eeb3d34717..9f3c4f6a2a343 100644
--- a/fs/ntfs3/frecord.c
+++ b/fs/ntfs3/frecord.c
@@ -102,7 +102,7 @@ void ni_clear(struct ntfs_inode *ni)
 {
 	struct rb_node *node;
 
-	if (!ni->vfs_inode.i_nlink && is_rec_inuse(ni->mi.mrec))
+	if (!ni->vfs_inode.i_nlink && ni->mi.mrec && is_rec_inuse(ni->mi.mrec))
 		ni_delete_all(ni);
 
 	al_destroy(ni);
-- 
2.39.2