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Subject[PATCH] [2.5] reiserfs: fix races between link and unlink on same file
Hello!

This patch (originally by Chris Mason) fixes link/unlink races in reiserfs.
The patch is against 2.6.0-test2, please apply.


===== fs/reiserfs/namei.c 1.47 vs edited =====
--- 1.47/fs/reiserfs/namei.c Mon Jun 30 10:49:04 2003
+++ edited/fs/reiserfs/namei.c Thu Jul 31 18:01:55 2003
@@ -822,6 +822,7 @@
int windex ;
struct reiserfs_transaction_handle th ;
int jbegin_count;
+ unsigned long savelink;

inode = dentry->d_inode;

@@ -858,11 +859,20 @@
inode->i_nlink = 1;
}

+ inode->i_nlink--;
+
+ /*
+ * we schedule before doing the add_save_link call, save the link
+ * count so we don't race
+ */
+ savelink = inode->i_nlink;
+
+
retval = reiserfs_cut_from_item (&th, &path, &(de.de_entry_key), dir, NULL, 0);
- if (retval < 0)
+ if (retval < 0) {
+ inode->i_nlink++;
goto end_unlink;
-
- inode->i_nlink--;
+ }
inode->i_ctime = CURRENT_TIME;
reiserfs_update_sd (&th, inode);

@@ -871,7 +881,7 @@
dir->i_ctime = dir->i_mtime = CURRENT_TIME;
reiserfs_update_sd (&th, dir);

- if (!inode->i_nlink)
+ if (!savelink)
/* prevent file from getting lost */
add_save_link (&th, inode, 0/* not truncate */);

@@ -976,6 +986,12 @@
reiserfs_write_unlock(dir->i_sb);
return -EMLINK;
}
+ if (inode->i_nlink == 0) {
+ return -ENOENT;
+ }
+
+ /* inc before scheduling so reiserfs_unlink knows we are here */
+ inode->i_nlink++;

journal_begin(&th, dir->i_sb, jbegin_count) ;
windex = push_journal_writer("reiserfs_link") ;
@@ -988,13 +1004,13 @@
reiserfs_update_inode_transaction(dir) ;

if (retval) {
+ inode->i_nlink--;
pop_journal_writer(windex) ;
journal_end(&th, dir->i_sb, jbegin_count) ;
reiserfs_write_unlock(dir->i_sb);
return retval;
}

- inode->i_nlink++;
inode->i_ctime = CURRENT_TIME;
reiserfs_update_sd (&th, inode);

@@ -1068,6 +1084,7 @@
struct reiserfs_transaction_handle th ;
int jbegin_count ;
umode_t old_inode_mode;
+ unsigned long savelink = 1;

/* two balancings: old name removal, new name insertion or "save" link,
stat data updates: old directory and new directory and maybe block
@@ -1246,6 +1263,7 @@
new_dentry_inode->i_nlink--;
}
new_dentry_inode->i_ctime = new_dir->i_ctime;
+ savelink = new_dentry_inode->i_nlink;
}

if (S_ISDIR(old_inode_mode)) {
@@ -1279,7 +1297,7 @@
reiserfs_update_sd (&th, new_dir);

if (new_dentry_inode) {
- if (new_dentry_inode->i_nlink == 0)
+ if (savelink == 0)
add_save_link (&th, new_dentry_inode, 0/* not truncate */);
reiserfs_update_sd (&th, new_dentry_inode);
}
-
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