[PATCH AUTOSEL 5.15 08/13] fs/ntfs3: Fix a possible null-pointer dereference in ni_clear()

[Sasha Levin]

From: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>

[ 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@xxxxxxxxx>
Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 95556515ded3d..d24e12d348d49 100644
--- a/fs/ntfs3/frecord.c
+++ b/fs/ntfs3/frecord.c
@@ -101,7 +101,7 @@ 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