From 9b7f375505f5611efb562065b57814b28a81abc3 Mon Sep 17 00:00:00 2001 From: Jeff Mahoney Date: Mon, 23 Apr 2007 14:41:17 -0700 Subject: reiserfs: fix xattr root locking/refcount bug The listxattr() and getxattr() operations are only protected by a read lock. As a result, if either of these operations run in parallel, a race condition exists where the xattr_root will end up being cached twice, which results in the leaking of a reference and a BUG() on umount. This patch refactors get_xa_root(), __get_xa_root(), and create_xa_root(), into one get_xa_root() function that takes the appropriate locking around the entire critical section. Reported, diagnosed and tested by Andrea Righi Signed-off-by: Jeff Mahoney Cc: Andrea Righi Cc: "Vladimir V. Saveliev" Cc: Edward Shishkin Cc: Alex Zarochentsev Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/reiserfs/xattr.c | 92 ++++++++++++++--------------------------------------- 1 file changed, 24 insertions(+), 68 deletions(-) diff --git a/fs/reiserfs/xattr.c b/fs/reiserfs/xattr.c index f01389fd162e..c8178b7b9212 100644 --- a/fs/reiserfs/xattr.c +++ b/fs/reiserfs/xattr.c @@ -54,82 +54,48 @@ static struct reiserfs_xattr_handler *find_xattr_handler_prefix(const char *prefix); -static struct dentry *create_xa_root(struct super_block *sb) +/* Returns the dentry referring to the root of the extended attribute + * directory tree. If it has already been retrieved, it is used. If it + * hasn't been created and the flags indicate creation is allowed, we + * attempt to create it. On error, we return a pointer-encoded error. + */ +static struct dentry *get_xa_root(struct super_block *sb, int flags) { struct dentry *privroot = dget(REISERFS_SB(sb)->priv_root); struct dentry *xaroot; /* This needs to be created at mount-time */ if (!privroot) - return ERR_PTR(-EOPNOTSUPP); + return ERR_PTR(-ENODATA); - xaroot = lookup_one_len(XAROOT_NAME, privroot, strlen(XAROOT_NAME)); - if (IS_ERR(xaroot)) { + mutex_lock(&privroot->d_inode->i_mutex); + if (REISERFS_SB(sb)->xattr_root) { + xaroot = dget(REISERFS_SB(sb)->xattr_root); goto out; - } else if (!xaroot->d_inode) { - int err; - mutex_lock(&privroot->d_inode->i_mutex); - err = - privroot->d_inode->i_op->mkdir(privroot->d_inode, xaroot, - 0700); - mutex_unlock(&privroot->d_inode->i_mutex); - - if (err) { - dput(xaroot); - dput(privroot); - return ERR_PTR(err); - } - REISERFS_SB(sb)->xattr_root = dget(xaroot); } - out: - dput(privroot); - return xaroot; -} - -/* This will return a dentry, or error, refering to the xa root directory. - * If the xa root doesn't exist yet, the dentry will be returned without - * an associated inode. This dentry can be used with ->mkdir to create - * the xa directory. */ -static struct dentry *__get_xa_root(struct super_block *s) -{ - struct dentry *privroot = dget(REISERFS_SB(s)->priv_root); - struct dentry *xaroot = NULL; - - if (IS_ERR(privroot) || !privroot) - return privroot; - xaroot = lookup_one_len(XAROOT_NAME, privroot, strlen(XAROOT_NAME)); if (IS_ERR(xaroot)) { goto out; } else if (!xaroot->d_inode) { - dput(xaroot); - xaroot = NULL; - goto out; + int err = -ENODATA; + if (flags == 0 || flags & XATTR_CREATE) + err = privroot->d_inode->i_op->mkdir(privroot->d_inode, + xaroot, 0700); + if (err) { + dput(xaroot); + xaroot = ERR_PTR(err); + goto out; + } } - - REISERFS_SB(s)->xattr_root = dget(xaroot); + REISERFS_SB(sb)->xattr_root = dget(xaroot); out: + mutex_unlock(&privroot->d_inode->i_mutex); dput(privroot); return xaroot; } -/* Returns the dentry (or NULL) referring to the root of the extended - * attribute directory tree. If it has already been retrieved, it is used. - * Otherwise, we attempt to retrieve it from disk. It may also return - * a pointer-encoded error. - */ -static inline struct dentry *get_xa_root(struct super_block *s) -{ - struct dentry *dentry = dget(REISERFS_SB(s)->xattr_root); - - if (!dentry) - dentry = __get_xa_root(s); - - return dentry; -} - /* Opens the directory corresponding to the inode's extended attribute store. * If flags allow, the tree to the directory may be created. If creation is * prohibited, -ENODATA is returned. */ @@ -138,21 +104,11 @@ static struct dentry *open_xa_dir(const struct inode *inode, int flags) struct dentry *xaroot, *xadir; char namebuf[17]; - xaroot = get_xa_root(inode->i_sb); - if (IS_ERR(xaroot)) { + xaroot = get_xa_root(inode->i_sb, flags); + if (IS_ERR(xaroot)) return xaroot; - } else if (!xaroot) { - if (flags == 0 || flags & XATTR_CREATE) { - xaroot = create_xa_root(inode->i_sb); - if (IS_ERR(xaroot)) - return xaroot; - } - if (!xaroot) - return ERR_PTR(-ENODATA); - } /* ok, we have xaroot open */ - snprintf(namebuf, sizeof(namebuf), "%X.%X", le32_to_cpu(INODE_PKEY(inode)->k_objectid), inode->i_generation); @@ -821,7 +777,7 @@ int reiserfs_delete_xattrs(struct inode *inode) /* Leftovers besides . and .. -- that's not good. */ if (dir->d_inode->i_nlink <= 2) { - root = get_xa_root(inode->i_sb); + root = get_xa_root(inode->i_sb, XATTR_REPLACE); reiserfs_write_lock_xattrs(inode->i_sb); err = vfs_rmdir(root->d_inode, dir); reiserfs_write_unlock_xattrs(inode->i_sb); -- cgit v1.2.3-59-g8ed1b