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expose a low-level variant of fd_install() for binder

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Similar situation to that of __alloc_fd(); do not use unless you
really have to.  You should not touch any descriptor table other
than your own; it's a sure sign of a really bad API design.

As with __alloc_fd(), you *must* use a first-class reference to
struct files_struct; something obtained by get_files_struct(some task)
(let alone direct task->files) will not do.  It must be either
current->files, or obtained by get_files_struct(current) by the
owner of that sucker and given to you.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2012-08-15 21:06:33 -04:00
parent 56007cae94
commit f869e8a7f7
3 changed files with 18 additions and 13 deletions
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13
drivers/staging/android/binder.c
View File

@ -386,17 +386,8 @@ int task_get_unused_fd_flags(struct binder_proc *proc, int flags)
static void task_fd_install(
struct binder_proc *proc, unsigned int fd, struct file *file)
{
struct files_struct *files = proc->files;
struct fdtable *fdt;
if (files == NULL)
return;
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);
if (proc->files)
__fd_install(proc->files, fd, file);
}
/*

16
fs/file.c
View File

@ -599,11 +599,18 @@ EXPORT_SYMBOL(put_unused_fd);
*
* 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(unsigned int fd, struct file *file)
void __fd_install(struct files_struct *files, unsigned int fd,
struct file *file)
{
struct files_struct *files = current->files;
struct fdtable *fdt;
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
@ -612,4 +619,9 @@ void fd_install(unsigned int fd, struct file *file)
spin_unlock(&files->file_lock);
}
void fd_install(unsigned int fd, struct file *file)
{
__fd_install(current->files, fd, file);
}
EXPORT_SYMBOL(fd_install);

2
include/linux/fdtable.h
View File

@ -121,6 +121,8 @@ struct files_struct *dup_fd(struct files_struct *, int *);
extern int __alloc_fd(struct files_struct *files,
unsigned start, unsigned end, unsigned flags);
extern void __fd_install(struct files_struct *files,
unsigned int fd, struct file *file);
extern struct kmem_cache *files_cachep;