[PATCH] ubifs: Fix a potential space leak problem while linking tmpfile

From: Zhihao Cheng
Date: Wed Jul 01 2020 - 05:31:50 EST


There is a potential space leak problem while linking tmpfile, in which
case, inode node (with nlink=0) is valid in tnc (on flash), which leads
to space leak. Meanwhile, the corresponding data nodes won't be released
from tnc. For example, (A reproducer can be found in Link):

$ mount UBIFS
[process A] [process B] [TNC] [orphan area]

ubifs_tmpfile inode_A (nlink=0) inode_A
do_commit inode_A (nlink=0) inode_A
â
(comment: It makes sure not replay inode_A in next mount)
ubifs_link inode_A (nlink=0) inode_A
ubifs_delete_orphan inode_A (nlink=0)
do_commit inode_A (nlink=0)
---> POWERCUT <---
(ubifs_jnl_update)

$ mount UBIFS
inode_A will neither be replayed in ubifs_replay_journal() nor
ubifs_mount_orphans(). inode_A (nlink=0) with its data nodes will
always on tnc, it occupy space but is non-visable for users.

Commit ee1438ce5dc4d ("ubifs: Check link count of inodes when killing
orphans.") handles problem in mistakenly deleting relinked tmpfile
while replaying orphan area. Since that, tmpfile inode should always
live in orphan area even it is linked. Fix it by reverting commit
32fe905c17f001 ("ubifs: Fix O_TMPFILE corner case in ubifs_link()").

Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: 32fe905c17f001 ("ubifs: Fix O_TMPFILE corner case in ubifs_link()")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=208405
---
fs/ubifs/dir.c | 7 -------
1 file changed, 7 deletions(-)

diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
index ef85ec167a84..9534c4bb598f 100644
--- a/fs/ubifs/dir.c
+++ b/fs/ubifs/dir.c
@@ -722,11 +722,6 @@ static int ubifs_link(struct dentry *old_dentry, struct inode *dir,
goto out_fname;

lock_2_inodes(dir, inode);
-
- /* Handle O_TMPFILE corner case, it is allowed to link a O_TMPFILE. */
- if (inode->i_nlink == 0)
- ubifs_delete_orphan(c, inode->i_ino);
-
inc_nlink(inode);
ihold(inode);
inode->i_ctime = current_time(inode);
@@ -747,8 +742,6 @@ static int ubifs_link(struct dentry *old_dentry, struct inode *dir,
dir->i_size -= sz_change;
dir_ui->ui_size = dir->i_size;
drop_nlink(inode);
- if (inode->i_nlink == 0)
- ubifs_add_orphan(c, inode->i_ino);
unlock_2_inodes(dir, inode);
ubifs_release_budget(c, &req);
iput(inode);
--
2.25.4