From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: From: Amir Goldstein Subject: [PATCH 2/2] locks: eliminate false positive conflicts for write lease Date: Sat, 8 Jun 2019 16:57:17 +0300 Message-Id: <20190608135717.8472-3-amir73il@gmail.com> In-Reply-To: <20190608135717.8472-1-amir73il@gmail.com> References: <20190608135717.8472-1-amir73il@gmail.com> To: Miklos Szeredi Cc: "J . Bruce Fields" , Jeff Layton , Mimi Zohar , Al Viro , linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org, linux-integrity@vger.kernel.org List-ID: check_conflicting_open() is checking for existing fd's open for read or for write before allowing to take a write lease. The check that was implemented using i_count and d_count is an approximation that has several false positives. For example, overlayfs since v4.19, takes an extra reference on the dentry; An open with O_PATH takes a reference on the inode and dentry although the file cannot be read nor written. Change the implementation to use inode_is_open_rdonly() and i_writecount to eliminate the false positive conflicts and allow a write lease to be taken on an overlayfs file. The change of behavior with existing fd's open with O_PATH is symmetric w.r.t. current behavior of lease breakers - an open with O_PATH currently does not break a write lease. Cc: # v4.19 Signed-off-by: Amir Goldstein --- fs/locks.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index ec1e4a5df629..4937cfdf611a 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -1753,10 +1753,10 @@ int fcntl_getlease(struct file *filp) } /** - * check_conflicting_open - see if the given dentry points to a file that has + * check_conflicting_open - see if the given file points to an inode that has * an existing open that would conflict with the * desired lease. - * @dentry: dentry to check + * @filp: file to check * @arg: type of lease that we're trying to acquire * @flags: current lock flags * @@ -1764,10 +1764,11 @@ int fcntl_getlease(struct file *filp) * conflict with the lease we're trying to set. */ static int -check_conflicting_open(const struct dentry *dentry, const long arg, int flags) +check_conflicting_open(struct file *filp, const long arg, int flags) { int ret = 0; - struct inode *inode = dentry->d_inode; + struct inode *inode = locks_inode(filp); + int self_wcount = 0, self_rcount = 0; if (flags & FL_LAYOUT) return 0; @@ -1775,8 +1776,14 @@ check_conflicting_open(const struct dentry *dentry, const long arg, int flags) if ((arg == F_RDLCK) && inode_is_open_for_write(inode)) return -EAGAIN; - if ((arg == F_WRLCK) && ((d_count(dentry) > 1) || - (atomic_read(&inode->i_count) > 1))) + /* Make sure that only read/write count is from lease requestor */ + if (filp->f_mode & FMODE_WRITE) + self_wcount = 1; + else if ((filp->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) + self_rcount = 1; + + if ((arg == F_WRLCK) && (i_readcount_read(inode) != self_rcount || + (atomic_read(&inode->i_writecount) != self_wcount))) ret = -EAGAIN; return ret; @@ -1786,8 +1793,7 @@ static int generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **priv) { struct file_lock *fl, *my_fl = NULL, *lease; - struct dentry *dentry = filp->f_path.dentry; - struct inode *inode = dentry->d_inode; + struct inode *inode = locks_inode(filp); struct file_lock_context *ctx; bool is_deleg = (*flp)->fl_flags & FL_DELEG; int error; @@ -1822,7 +1828,7 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr percpu_down_read(&file_rwsem); spin_lock(&ctx->flc_lock); time_out_leases(inode, &dispose); - error = check_conflicting_open(dentry, arg, lease->fl_flags); + error = check_conflicting_open(filp, arg, lease->fl_flags); if (error) goto out; @@ -1879,7 +1885,7 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr * precedes these checks. */ smp_mb(); - error = check_conflicting_open(dentry, arg, lease->fl_flags); + error = check_conflicting_open(filp, arg, lease->fl_flags); if (error) { locks_unlink_lock_ctx(lease); goto out; -- 2.17.1