diff options
Diffstat (limited to 'fs/file.c')
| -rw-r--r-- | fs/file.c | 573 |
1 files changed, 549 insertions, 24 deletions
diff --git a/fs/file.c b/fs/file.c index ba3f6053025c..0f1bda4bebfa 100644 --- a/fs/file.c +++ b/fs/file.c @@ -6,6 +6,7 @@ * Manage the dynamic fd arrays in the process files_struct. */ +#include <linux/syscalls.h> #include <linux/export.h> #include <linux/fs.h> #include <linux/mm.h> @@ -84,22 +85,14 @@ static void free_fdtable_work(struct work_struct *work) } } -void free_fdtable_rcu(struct rcu_head *rcu) +static void free_fdtable_rcu(struct rcu_head *rcu) { struct fdtable *fdt = container_of(rcu, struct fdtable, rcu); struct fdtable_defer *fddef; BUG_ON(!fdt); + BUG_ON(fdt->max_fds <= NR_OPEN_DEFAULT); - if (fdt->max_fds <= NR_OPEN_DEFAULT) { - /* - * This fdtable is embedded in the files structure and that - * structure itself is getting destroyed. - */ - kmem_cache_free(files_cachep, - container_of(fdt, struct files_struct, fdtab)); - return; - } if (!is_vmalloc_addr(fdt->fd) && !is_vmalloc_addr(fdt->open_fds)) { kfree(fdt->fd); kfree(fdt->open_fds); @@ -229,7 +222,7 @@ static int expand_fdtable(struct files_struct *files, int nr) copy_fdtable(new_fdt, cur_fdt); rcu_assign_pointer(files->fdt, new_fdt); if (cur_fdt->max_fds > NR_OPEN_DEFAULT) - free_fdtable(cur_fdt); + call_rcu(&cur_fdt->rcu, free_fdtable_rcu); } else { /* Somebody else expanded, so undo our attempt */ __free_fdtable(new_fdt); @@ -245,19 +238,12 @@ static int expand_fdtable(struct files_struct *files, int nr) * expanded and execution may have blocked. * The files->file_lock should be held on entry, and will be held on exit. */ -int expand_files(struct files_struct *files, int nr) +static int expand_files(struct files_struct *files, int nr) { struct fdtable *fdt; fdt = files_fdtable(files); - /* - * N.B. For clone tasks sharing a files structure, this test - * will limit the total number of files that can be opened. - */ - if (nr >= rlimit(RLIMIT_NOFILE)) - return -EMFILE; - /* Do we need to expand? */ if (nr < fdt->max_fds) return 0; @@ -270,6 +256,26 @@ int expand_files(struct files_struct *files, int nr) return expand_fdtable(files, nr); } +static inline void __set_close_on_exec(int fd, struct fdtable *fdt) +{ + __set_bit(fd, fdt->close_on_exec); +} + +static inline void __clear_close_on_exec(int fd, struct fdtable *fdt) +{ + __clear_bit(fd, fdt->close_on_exec); +} + +static inline void __set_open_fd(int fd, struct fdtable *fdt) +{ + __set_bit(fd, fdt->open_fds); +} + +static inline void __clear_open_fd(int fd, struct fdtable *fdt) +{ + __clear_bit(fd, fdt->open_fds); +} + static int count_open_files(struct fdtable *fdt) { int size = fdt->max_fds; @@ -395,6 +401,95 @@ out: return NULL; } +static void close_files(struct files_struct * files) +{ + int i, j; + struct fdtable *fdt; + + j = 0; + + /* + * It is safe to dereference the fd table without RCU or + * ->file_lock because this is the last reference to the + * files structure. But use RCU to shut RCU-lockdep up. + */ + rcu_read_lock(); + fdt = files_fdtable(files); + rcu_read_unlock(); + for (;;) { + unsigned long set; + i = j * BITS_PER_LONG; + if (i >= fdt->max_fds) + break; + set = fdt->open_fds[j++]; + while (set) { + if (set & 1) { + struct file * file = xchg(&fdt->fd[i], NULL); + if (file) { + filp_close(file, files); + cond_resched(); + } + } + i++; + set >>= 1; + } + } +} + +struct files_struct *get_files_struct(struct task_struct *task) +{ + struct files_struct *files; + + task_lock(task); + files = task->files; + if (files) + atomic_inc(&files->count); + task_unlock(task); + + return files; +} + +void put_files_struct(struct files_struct *files) +{ + struct fdtable *fdt; + + if (atomic_dec_and_test(&files->count)) { + close_files(files); + /* not really needed, since nobody can see us */ + rcu_read_lock(); + fdt = files_fdtable(files); + rcu_read_unlock(); + /* free the arrays if they are not embedded */ + if (fdt != &files->fdtab) + __free_fdtable(fdt); + kmem_cache_free(files_cachep, files); + } +} + +void reset_files_struct(struct files_struct *files) +{ + struct task_struct *tsk = current; + struct files_struct *old; + + old = tsk->files; + task_lock(tsk); + tsk->files = files; + task_unlock(tsk); + put_files_struct(old); +} + +void exit_files(struct task_struct *tsk) +{ + struct files_struct * files = tsk->files; + + if (files) { + task_lock(tsk); + tsk->files = NULL; + task_unlock(tsk); + put_files_struct(files); + } +} + static void __devinit fdtable_defer_list_init(int cpu) { struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu); @@ -424,12 +519,18 @@ struct files_struct init_files = { .file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock), }; +void daemonize_descriptors(void) +{ + atomic_inc(&init_files.count); + reset_files_struct(&init_files); +} + /* * allocate a file descriptor, mark it busy. */ -int alloc_fd(unsigned start, unsigned flags) +int __alloc_fd(struct files_struct *files, + unsigned start, unsigned end, unsigned flags) { - struct files_struct *files = current->files; unsigned int fd; int error; struct fdtable *fdt; @@ -444,6 +545,14 @@ repeat: if (fd < fdt->max_fds) fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd); + /* + * N.B. For clone tasks sharing a files structure, this test + * will limit the total number of files that can be opened. + */ + error = -EMFILE; + if (fd >= end) + goto out; + error = expand_files(files, fd); if (error < 0) goto out; @@ -477,8 +586,424 @@ out: return error; } -int get_unused_fd(void) +static int alloc_fd(unsigned start, unsigned flags) +{ + return __alloc_fd(current->files, start, rlimit(RLIMIT_NOFILE), flags); +} + +int get_unused_fd_flags(unsigned flags) +{ + return __alloc_fd(current->files, 0, rlimit(RLIMIT_NOFILE), flags); +} +EXPORT_SYMBOL(get_unused_fd_flags); + +static void __put_unused_fd(struct files_struct *files, unsigned int fd) +{ + struct fdtable *fdt = files_fdtable(files); + __clear_open_fd(fd, fdt); + if (fd < files->next_fd) + files->next_fd = fd; +} + +void put_unused_fd(unsigned int fd) +{ + struct files_struct *files = current->files; + spin_lock(&files->file_lock); + __put_unused_fd(files, fd); + spin_unlock(&files->file_lock); +} + +EXPORT_SYMBOL(put_unused_fd); + +/* + * Install a file pointer in the fd array. + * + * The VFS is full of places where we drop the files lock between + * setting the open_fds bitmap and installing the file in the file + * array. At any such point, we are vulnerable to a dup2() race + * installing a file in the array before us. We need to detect this and + * fput() the struct file we are about to overwrite in this case. + * + * It should never happen - if we allow dup2() do it, _really_ bad things + * will follow. + * + * NOTE: __fd_install() variant is really, really low-level; don't + * use it unless you are forced to by truly lousy API shoved down + * your throat. 'files' *MUST* be either current->files or obtained + * by get_files_struct(current) done by whoever had given it to you, + * or really bad things will happen. Normally you want to use + * fd_install() instead. + */ + +void __fd_install(struct files_struct *files, unsigned int fd, + struct file *file) +{ + struct fdtable *fdt; + spin_lock(&files->file_lock); + fdt = files_fdtable(files); + BUG_ON(fdt->fd[fd] != NULL); + rcu_assign_pointer(fdt->fd[fd], file); + spin_unlock(&files->file_lock); +} + +void fd_install(unsigned int fd, struct file *file) { - return alloc_fd(0, 0); + __fd_install(current->files, fd, file); +} + +EXPORT_SYMBOL(fd_install); + +/* + * The same warnings as for __alloc_fd()/__fd_install() apply here... + */ +int __close_fd(struct files_struct *files, unsigned fd) +{ + struct file *file; + struct fdtable *fdt; + + spin_lock(&files->file_lock); + fdt = files_fdtable(files); + if (fd >= fdt->max_fds) + goto out_unlock; + file = fdt->fd[fd]; + if (!file) + goto out_unlock; + rcu_assign_pointer(fdt->fd[fd], NULL); + __clear_close_on_exec(fd, fdt); + __put_unused_fd(files, fd); + spin_unlock(&files->file_lock); + return filp_close(file, files); + +out_unlock: + spin_unlock(&files->file_lock); + return -EBADF; +} + +void do_close_on_exec(struct files_struct *files) +{ + unsigned i; + struct fdtable *fdt; + + /* exec unshares first */ + BUG_ON(atomic_read(&files->count) != 1); + spin_lock(&files->file_lock); + for (i = 0; ; i++) { + unsigned long set; + unsigned fd = i * BITS_PER_LONG; + fdt = files_fdtable(files); + if (fd >= fdt->max_fds) + break; + set = fdt->close_on_exec[i]; + if (!set) + continue; + fdt->close_on_exec[i] = 0; + for ( ; set ; fd++, set >>= 1) { + struct file *file; + if (!(set & 1)) + continue; + file = fdt->fd[fd]; + if (!file) + continue; + rcu_assign_pointer(fdt->fd[fd], NULL); + __put_unused_fd(files, fd); + spin_unlock(&files->file_lock); + filp_close(file, files); + cond_resched(); + spin_lock(&files->file_lock); + } + + } + spin_unlock(&files->file_lock); +} + +struct file *fget(unsigned int fd) +{ + struct file *file; + struct files_struct *files = current->files; + + rcu_read_lock(); + file = fcheck_files(files, fd); + if (file) { + /* File object ref couldn't be taken */ + if (file->f_mode & FMODE_PATH || + !atomic_long_inc_not_zero(&file->f_count)) + file = NULL; + } + rcu_read_unlock(); + + return file; +} + +EXPORT_SYMBOL(fget); + +struct file *fget_raw(unsigned int fd) +{ + struct file *file; + struct files_struct *files = current->files; + + rcu_read_lock(); + file = fcheck_files(files, fd); + if (file) { + /* File object ref couldn't be taken */ + if (!atomic_long_inc_not_zero(&file->f_count)) + file = NULL; + } + rcu_read_unlock(); + + return file; +} + +EXPORT_SYMBOL(fget_raw); + +/* + * Lightweight file lookup - no refcnt increment if fd table isn't shared. + * + * You can use this instead of fget if you satisfy all of the following + * conditions: + * 1) You must call fput_light before exiting the syscall and returning control + * to userspace (i.e. you cannot remember the returned struct file * after + * returning to userspace). + * 2) You must not call filp_close on the returned struct file * in between + * calls to fget_light and fput_light. + * 3) You must not clone the current task in between the calls to fget_light + * and fput_light. + * + * The fput_needed flag returned by fget_light should be passed to the + * corresponding fput_light. + */ +struct file *fget_light(unsigned int fd, int *fput_needed) +{ + struct file *file; + struct files_struct *files = current->files; + + *fput_needed = 0; + if (atomic_read(&files->count) == 1) { + file = fcheck_files(files, fd); + if (file && (file->f_mode & FMODE_PATH)) + file = NULL; + } else { + rcu_read_lock(); + file = fcheck_files(files, fd); + if (file) { + if (!(file->f_mode & FMODE_PATH) && + atomic_long_inc_not_zero(&file->f_count)) + *fput_needed = 1; + else + /* Didn't get the reference, someone's freed */ + file = NULL; + } + rcu_read_unlock(); + } + + return file; +} +EXPORT_SYMBOL(fget_light); + +struct file *fget_raw_light(unsigned int fd, int *fput_needed) +{ + struct file *file; + struct files_struct *files = current->files; + + *fput_needed = 0; + if (atomic_read(&files->count) == 1) { + file = fcheck_files(files, fd); + } else { + rcu_read_lock(); + file = fcheck_files(files, fd); + if (file) { + if (atomic_long_inc_not_zero(&file->f_count)) + *fput_needed = 1; + else + /* Didn't get the reference, someone's freed */ + file = NULL; + } + rcu_read_unlock(); + } + + return file; +} + +void set_close_on_exec(unsigned int fd, int flag) +{ + struct files_struct *files = current->files; + struct fdtable *fdt; + spin_lock(&files->file_lock); + fdt = files_fdtable(files); + if (flag) + __set_close_on_exec(fd, fdt); + else + __clear_close_on_exec(fd, fdt); + spin_unlock(&files->file_lock); +} + +bool get_close_on_exec(unsigned int fd) +{ + struct files_struct *files = current->files; + struct fdtable *fdt; + bool res; + rcu_read_lock(); + fdt = files_fdtable(files); + res = close_on_exec(fd, fdt); + rcu_read_unlock(); + return res; +} + +static int do_dup2(struct files_struct *files, + struct file *file, unsigned fd, unsigned flags) +{ + struct file *tofree; + struct fdtable *fdt; + + /* + * 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. + */ + fdt = files_fdtable(files); + tofree = fdt->fd[fd]; + if (!tofree && fd_is_open(fd, fdt)) + goto Ebusy; + get_file(file); + rcu_assign_pointer(fdt->fd[fd], file); + __set_open_fd(fd, fdt); + if (flags & O_CLOEXEC) + __set_close_on_exec(fd, fdt); + else + __clear_close_on_exec(fd, fdt); + spin_unlock(&files->file_lock); + + if (tofree) + filp_close(tofree, files); + + return fd; + +Ebusy: + spin_unlock(&files->file_lock); + return -EBUSY; +} + +int replace_fd(unsigned fd, struct file *file, unsigned flags) +{ + int err; + struct files_struct *files = current->files; + + if (!file) + return __close_fd(files, fd); + + if (fd >= rlimit(RLIMIT_NOFILE)) + return -EMFILE; + + spin_lock(&files->file_lock); + err = expand_files(files, fd); + if (unlikely(err < 0)) + goto out_unlock; + return do_dup2(files, file, fd, flags); + +out_unlock: + spin_unlock(&files->file_lock); + return err; +} + +SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags) +{ + int err = -EBADF; + struct file *file; + struct files_struct *files = current->files; + + if ((flags & ~O_CLOEXEC) != 0) + return -EINVAL; + + if (newfd >= rlimit(RLIMIT_NOFILE)) + return -EMFILE; + + spin_lock(&files->file_lock); + err = expand_files(files, newfd); + file = fcheck(oldfd); + if (unlikely(!file)) + goto Ebadf; + if (unlikely(err < 0)) { + if (err == -EMFILE) + goto Ebadf; + goto out_unlock; + } + return do_dup2(files, file, newfd, flags); + +Ebadf: + err = -EBADF; +out_unlock: + spin_unlock(&files->file_lock); + return err; +} + +SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd) +{ + if (unlikely(newfd == oldfd)) { /* corner case */ + struct files_struct *files = current->files; + int retval = oldfd; + + rcu_read_lock(); + if (!fcheck_files(files, oldfd)) + retval = -EBADF; + rcu_read_unlock(); + return retval; + } + return sys_dup3(oldfd, newfd, 0); +} + +SYSCALL_DEFINE1(dup, unsigned int, fildes) +{ + int ret = -EBADF; + struct file *file = fget_raw(fildes); + + if (file) { + ret = get_unused_fd(); + if (ret >= 0) + fd_install(ret, file); + else + fput(file); + } + return ret; +} + +int f_dupfd(unsigned int from, struct file *file, unsigned flags) +{ + int err; + if (from >= rlimit(RLIMIT_NOFILE)) + return -EINVAL; + err = alloc_fd(from, flags); + if (err >= 0) { + get_file(file); + fd_install(err, file); + } + return err; +} + +int iterate_fd(struct files_struct *files, unsigned n, + int (*f)(const void *, struct file *, unsigned), + const void *p) +{ + struct fdtable *fdt; + struct file *file; + int res = 0; + if (!files) + return 0; + spin_lock(&files->file_lock); + fdt = files_fdtable(files); + while (!res && n < fdt->max_fds) { + file = rcu_dereference_check_fdtable(files, fdt->fd[n++]); + if (file) + res = f(p, file, n); + } + spin_unlock(&files->file_lock); + return res; } -EXPORT_SYMBOL(get_unused_fd); +EXPORT_SYMBOL(iterate_fd); |