From 7f3697e24dc3820b10f445a4a7d914fc356012d1 Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Thu, 7 Jan 2016 16:38:10 -0500 Subject: [PATCH] locks: fix unlock when fcntl_setlk races with a close Dmitry reported that he was able to reproduce the WARN_ON_ONCE that fires in locks_free_lock_context when the flc_posix list isn't empty. The problem turns out to be that we're basically rebuilding the file_lock from scratch in fcntl_setlk when we discover that the setlk has raced with a close. If the l_whence field is SEEK_CUR or SEEK_END, then we may end up with fl_start and fl_end values that differ from when the lock was initially set, if the file position or length of the file has changed in the interim. Fix this by just reusing the same lock request structure, and simply override fl_type value with F_UNLCK as appropriate. That ensures that we really are unlocking the lock that was initially set. While we're there, make sure that we do pop a WARN_ON_ONCE if the removal ever fails. Also return -EBADF in this event, since that's what we would have returned if the close had happened earlier. Cc: Alexander Viro Cc: Fixes: c293621bbf67 (stale POSIX lock handling) Reported-by: Dmitry Vyukov Signed-off-by: Jeff Layton Acked-by: "J. Bruce Fields" --- fs/locks.c | 51 ++++++++++++++++++++++++++++++--------------------- 1 file changed, 30 insertions(+), 21 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index 593dca300b29..c263aff793bc 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -2181,7 +2181,6 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd, goto out; } -again: error = flock_to_posix_lock(filp, file_lock, &flock); if (error) goto out; @@ -2223,19 +2222,22 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd, * Attempt to detect a close/fcntl race and recover by * releasing the lock that was just acquired. */ - /* - * we need that spin_lock here - it prevents reordering between - * update of i_flctx->flc_posix and check for it done in close(). - * rcu_read_lock() wouldn't do. - */ - spin_lock(¤t->files->file_lock); - f = fcheck(fd); - spin_unlock(¤t->files->file_lock); - if (!error && f != filp && flock.l_type != F_UNLCK) { - flock.l_type = F_UNLCK; - goto again; + if (!error && file_lock->fl_type != F_UNLCK) { + /* + * We need that spin_lock here - it prevents reordering between + * update of i_flctx->flc_posix and check for it done in + * close(). rcu_read_lock() wouldn't do. + */ + spin_lock(¤t->files->file_lock); + f = fcheck(fd); + spin_unlock(¤t->files->file_lock); + if (f != filp) { + file_lock->fl_type = F_UNLCK; + error = do_lock_file_wait(filp, cmd, file_lock); + WARN_ON_ONCE(error); + error = -EBADF; + } } - out: locks_free_lock(file_lock); return error; @@ -2321,7 +2323,6 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd, goto out; } -again: error = flock64_to_posix_lock(filp, file_lock, &flock); if (error) goto out; @@ -2363,14 +2364,22 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd, * Attempt to detect a close/fcntl race and recover by * releasing the lock that was just acquired. */ - spin_lock(¤t->files->file_lock); - f = fcheck(fd); - spin_unlock(¤t->files->file_lock); - if (!error && f != filp && flock.l_type != F_UNLCK) { - flock.l_type = F_UNLCK; - goto again; + if (!error && file_lock->fl_type != F_UNLCK) { + /* + * We need that spin_lock here - it prevents reordering between + * update of i_flctx->flc_posix and check for it done in + * close(). rcu_read_lock() wouldn't do. + */ + spin_lock(¤t->files->file_lock); + f = fcheck(fd); + spin_unlock(¤t->files->file_lock); + if (f != filp) { + file_lock->fl_type = F_UNLCK; + error = do_lock_file_wait(filp, cmd, file_lock); + WARN_ON_ONCE(error); + error = -EBADF; + } } - out: locks_free_lock(file_lock); return error; -- GitLab