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New locking/refcounting for fs_struct

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* all changes of current->fs are done under task_lock and write_lock of
  old fs->lock
* refcount is not atomic anymore (same protection)
* its decrements are done when removing reference from current; at the
  same time we decide whether to free it.
* put_fs_struct() is gone
* new field - ->in_exec.  Set by check_unsafe_exec() if we are trying to do
  execve() and only subthreads share fs_struct.  Cleared when finishing exec
  (success and failure alike).  Makes CLONE_FS fail with -EAGAIN if set.
* check_unsafe_exec() may fail with -EAGAIN if another execve() from subthread
  is in progress.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2009-03-30 07:20:30 -04:00
parent 3e93cd6718
commit 498052bba5
7 changed files with 121 additions and 44 deletions
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8
include/linux/fs_struct.h
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@ -4,12 +4,10 @@
#include <linux/path.h>
struct fs_struct {
atomic_t count; /* This usage count is used by check_unsafe_exec() for
* security checking purposes - therefore it may not be
* incremented, except by clone(CLONE_FS).
*/
int users;
rwlock_t lock;
int umask;
int in_exec;
struct path root, pwd;
};
@ -19,7 +17,7 @@ extern void exit_fs(struct task_struct *);
extern void set_fs_root(struct fs_struct *, struct path *);
extern void set_fs_pwd(struct fs_struct *, struct path *);
extern struct fs_struct *copy_fs_struct(struct fs_struct *);
extern void put_fs_struct(struct fs_struct *);
extern void free_fs_struct(struct fs_struct *);
extern void daemonize_fs_struct(void);
extern int unshare_fs_struct(void);