From e869332d2e5bb766cc6ac636a5594d2208e11baf Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Fri, 28 Jun 2013 14:15:14 +0300 Subject: [PATCH] UBIFS: prepare to fix a horrid bug commit 33f1a63ae84dfd9ad298cf275b8f1887043ced36 upstream. Al Viro pointed me to the fact that '->readdir()' and '->llseek()' have no mutual exclusion, which means the 'ubifs_dir_llseek()' can be run while we are in the middle of 'ubifs_readdir()'. First of all, this means that 'file->private_data' can be freed while 'ubifs_readdir()' uses it. But this particular patch does not fix the problem. This patch is only a preparation, and the fix will follow next. In this patch we make 'ubifs_readdir()' stop using 'file->f_pos' directly, because 'file->f_pos' can be changed by '->llseek()' at any point. This may lead 'ubifs_readdir()' to returning inconsistent data: directory entry names may correspond to incorrect file positions. So here we introduce a local variable 'pos', read 'file->f_pose' once at very the beginning, and then stick to 'pos'. The result of this is that when 'ubifs_dir_llseek()' changes 'file->f_pos' while we are in the middle of 'ubifs_readdir()', the latter "wins". Reported-by: Al Viro Tested-by: Artem Bityutskiy Signed-off-by: Artem Bityutskiy Signed-off-by: Al Viro [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- fs/ubifs/dir.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c index 683492043317..12a2caf3f1b3 100644 --- a/fs/ubifs/dir.c +++ b/fs/ubifs/dir.c @@ -357,15 +357,16 @@ static unsigned int vfs_dent_type(uint8_t type) static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir) { int err, over = 0; + loff_t pos = file->f_pos; struct qstr nm; union ubifs_key key; struct ubifs_dent_node *dent; struct inode *dir = file->f_path.dentry->d_inode; struct ubifs_info *c = dir->i_sb->s_fs_info; - dbg_gen("dir ino %lu, f_pos %#llx", dir->i_ino, file->f_pos); + dbg_gen("dir ino %lu, f_pos %#llx", dir->i_ino, pos); - if (file->f_pos > UBIFS_S_KEY_HASH_MASK || file->f_pos == 2) + if (pos > UBIFS_S_KEY_HASH_MASK || pos == 2) /* * The directory was seek'ed to a senseless position or there * are no more entries. @@ -373,15 +374,15 @@ static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir) return 0; /* File positions 0 and 1 correspond to "." and ".." */ - if (file->f_pos == 0) { + if (pos == 0) { ubifs_assert(!file->private_data); over = filldir(dirent, ".", 1, 0, dir->i_ino, DT_DIR); if (over) return 0; - file->f_pos = 1; + file->f_pos = pos = 1; } - if (file->f_pos == 1) { + if (pos == 1) { ubifs_assert(!file->private_data); over = filldir(dirent, "..", 2, 1, parent_ino(file->f_path.dentry), DT_DIR); @@ -397,7 +398,7 @@ static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir) goto out; } - file->f_pos = key_hash_flash(c, &dent->key); + file->f_pos = pos = key_hash_flash(c, &dent->key); file->private_data = dent; } @@ -405,17 +406,16 @@ static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir) if (!dent) { /* * The directory was seek'ed to and is now readdir'ed. - * Find the entry corresponding to @file->f_pos or the - * closest one. + * Find the entry corresponding to @pos or the closest one. */ - dent_key_init_hash(c, &key, dir->i_ino, file->f_pos); + dent_key_init_hash(c, &key, dir->i_ino, pos); nm.name = NULL; dent = ubifs_tnc_next_ent(c, &key, &nm); if (IS_ERR(dent)) { err = PTR_ERR(dent); goto out; } - file->f_pos = key_hash_flash(c, &dent->key); + file->f_pos = pos = key_hash_flash(c, &dent->key); file->private_data = dent; } @@ -427,7 +427,7 @@ static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir) ubifs_inode(dir)->creat_sqnum); nm.len = le16_to_cpu(dent->nlen); - over = filldir(dirent, dent->name, nm.len, file->f_pos, + over = filldir(dirent, dent->name, nm.len, pos, le64_to_cpu(dent->inum), vfs_dent_type(dent->type)); if (over) @@ -443,7 +443,7 @@ static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir) } kfree(file->private_data); - file->f_pos = key_hash_flash(c, &dent->key); + file->f_pos = pos = key_hash_flash(c, &dent->key); file->private_data = dent; cond_resched(); } -- 2.30.2