diff options
| -rw-r--r-- | fs/fcntl.c | 53 |
1 files changed, 27 insertions, 26 deletions
diff --git a/fs/fcntl.c b/fs/fcntl.c index 2e40799daad..ac4f7db9f13 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -63,31 +63,35 @@ asmlinkage long sys_dup3(unsigned int oldfd, unsigned int newfd, int flags) return -EINVAL; spin_lock(&files->file_lock); - if (!(file = fcheck(oldfd))) - goto out_unlock; - get_file(file); /* We are now finished with oldfd */ - err = expand_files(files, newfd); + file = fcheck(oldfd); + if (unlikely(!file)) + goto Ebadf; if (unlikely(err < 0)) { if (err == -EMFILE) - err = -EBADF; - goto out_fput; + goto Ebadf; + goto out_unlock; } - - /* To avoid races with open() and dup(), we will mark the fd as - * in-use in the open-file bitmap throughout the entire dup2() - * process. This is quite safe: do_close() uses the fd array - * entry, not the bitmap, to decide what work needs to be - * done. --sct */ - /* Doesn't work. open() might be there first. --AV */ - - /* Yes. It's a race. In user space. Nothing sane to do */ + /* + * We need to detect attempts to do dup2() over allocated but still + * not finished descriptor. NB: OpenBSD avoids that at the price of + * extra work in their equivalent of fget() - they insert struct + * file immediately after grabbing descriptor, mark it larval if + * more work (e.g. actual opening) is needed and make sure that + * fget() treats larval files as absent. Potentially interesting, + * but while extra work in fget() is trivial, locking implications + * and amount of surgery on open()-related paths in VFS are not. + * FreeBSD fails with -EBADF in the same situation, NetBSD "solution" + * deadlocks in rather amusing ways, AFAICS. All of that is out of + * scope of POSIX or SUS, since neither considers shared descriptor + * tables and this condition does not arise without those. + */ err = -EBUSY; fdt = files_fdtable(files); tofree = fdt->fd[newfd]; if (!tofree && FD_ISSET(newfd, fdt->open_fds)) - goto out_fput; - + goto out_unlock; + get_file(file); rcu_assign_pointer(fdt->fd[newfd], file); FD_SET(newfd, fdt->open_fds); if (flags & O_CLOEXEC) @@ -98,17 +102,14 @@ asmlinkage long sys_dup3(unsigned int oldfd, unsigned int newfd, int flags) if (tofree) filp_close(tofree, files); - err = newfd; -out: - return err; -out_unlock: - spin_unlock(&files->file_lock); - goto out; -out_fput: + return newfd; + +Ebadf: + err = -EBADF; +out_unlock: spin_unlock(&files->file_lock); - fput(file); - goto out; + return err; } asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd) |