Commit 33f1a63a authored by Artem Bityutskiy's avatar Artem Bityutskiy Committed by Al Viro
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UBIFS: prepare to fix a horrid bug 



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".

Cc: stable@vger.kernel.org
Reported-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Tested-by: default avatarArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: default avatarArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 945fb136

fs/ubifs/dir.c

+12 −12
Original line number Diff line number Diff line
@@ -349,15 +349,16 @@ 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_inode(file);

	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.
@@ -365,15 +366,15 @@ 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);
@@ -389,7 +390,7 @@ 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;

	}
@@ -397,17 +398,16 @@ 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;

	}
@@ -419,7 +419,7 @@ 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)
@@ -435,7 +435,7 @@ 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();

	}

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