From 993dfa8776308dcfd311cf77a3bbed4aa11e9868 Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Fri, 31 Mar 2006 02:30:55 -0800 Subject: [PATCH] [PATCH] fs/locks.c: Fix sys_flock() race sys_flock() currently has a race which can result in a double free in the multi-thread case. Thread 1 Thread 2 sys_flock(file, LOCK_EX) sys_flock(file, LOCK_UN) If Thread 2 removes the lock from inode->i_lock before Thread 1 tests for list_empty(&lock->fl_link) at the end of sys_flock, then both threads will end up calling locks_free_lock for the same lock. Fix is to make flock_lock_file() do the same as posix_lock_file(), namely to make a copy of the request, so that the caller can always free the lock. This also has the side-effect of fixing up a reference problem in the lockd handling of flock. Signed-off-by: Trond Myklebust Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/locks.c | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index 8fcfeb177a2..dda83d6cd48 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -726,8 +726,9 @@ EXPORT_SYMBOL(posix_locks_deadlock); * at the head of the list, but that's secret knowledge known only to * flock_lock_file and posix_lock_file. */ -static int flock_lock_file(struct file *filp, struct file_lock *new_fl) +static int flock_lock_file(struct file *filp, struct file_lock *request) { + struct file_lock *new_fl = NULL; struct file_lock **before; struct inode * inode = filp->f_dentry->d_inode; int error = 0; @@ -742,17 +743,19 @@ static int flock_lock_file(struct file *filp, struct file_lock *new_fl) continue; if (filp != fl->fl_file) continue; - if (new_fl->fl_type == fl->fl_type) + if (request->fl_type == fl->fl_type) goto out; found = 1; locks_delete_lock(before); break; } - unlock_kernel(); - if (new_fl->fl_type == F_UNLCK) - return 0; + if (request->fl_type == F_UNLCK) + goto out; + new_fl = locks_alloc_lock(); + if (new_fl == NULL) + goto out; /* * If a higher-priority process was blocked on the old file lock, * give it the opportunity to lock the file. @@ -760,26 +763,27 @@ static int flock_lock_file(struct file *filp, struct file_lock *new_fl) if (found) cond_resched(); - lock_kernel(); for_each_lock(inode, before) { struct file_lock *fl = *before; if (IS_POSIX(fl)) break; if (IS_LEASE(fl)) continue; - if (!flock_locks_conflict(new_fl, fl)) + if (!flock_locks_conflict(request, fl)) continue; error = -EAGAIN; - if (new_fl->fl_flags & FL_SLEEP) { - locks_insert_block(fl, new_fl); - } + if (request->fl_flags & FL_SLEEP) + locks_insert_block(fl, request); goto out; } + locks_copy_lock(new_fl, request); locks_insert_lock(&inode->i_flock, new_fl); - error = 0; + new_fl = NULL; out: unlock_kernel(); + if (new_fl) + locks_free_lock(new_fl); return error; } @@ -1560,9 +1564,7 @@ asmlinkage long sys_flock(unsigned int fd, unsigned int cmd) error = flock_lock_file_wait(filp, lock); out_free: - if (list_empty(&lock->fl_link)) { - locks_free_lock(lock); - } + locks_free_lock(lock); out_putf: fput(filp); -- 2.20.1