New locking/refcounting for fs_struct

* 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

View file

@ -51,6 +51,7 @@
#include <linux/poll.h>
#include <linux/mm.h>
#include <linux/eventpoll.h>
#include <linux/fs_struct.h>
#include <asm/uaccess.h>
#include <asm/mmu_context.h>
@ -1441,12 +1442,15 @@ int compat_do_execve(char * filename,
bprm->cred = prepare_exec_creds();
if (!bprm->cred)
goto out_unlock;
check_unsafe_exec(bprm);
retval = check_unsafe_exec(bprm);
if (retval)
goto out_unlock;
file = open_exec(filename);
retval = PTR_ERR(file);
if (IS_ERR(file))
goto out_unlock;
goto out_unmark;
sched_exec();
@ -1488,6 +1492,9 @@ int compat_do_execve(char * filename,
goto out;
/* execve succeeded */
write_lock(&current->fs->lock);
current->fs->in_exec = 0;
write_unlock(&current->fs->lock);
current->in_execve = 0;
mutex_unlock(&current->cred_exec_mutex);
acct_update_integrals(current);
@ -1506,6 +1513,11 @@ out_file:
fput(bprm->file);
}
out_unmark:
write_lock(&current->fs->lock);
current->fs->in_exec = 0;
write_unlock(&current->fs->lock);
out_unlock:
current->in_execve = 0;
mutex_unlock(&current->cred_exec_mutex);

View file

@ -1056,16 +1056,18 @@ EXPORT_SYMBOL(install_exec_creds);
* - the caller must hold current->cred_exec_mutex to protect against
* PTRACE_ATTACH
*/
void check_unsafe_exec(struct linux_binprm *bprm)
int check_unsafe_exec(struct linux_binprm *bprm)
{
struct task_struct *p = current, *t;
unsigned long flags;
unsigned n_fs, n_sighand;
int res = 0;
bprm->unsafe = tracehook_unsafe_exec(p);
n_fs = 1;
n_sighand = 1;
write_lock(&p->fs->lock);
lock_task_sighand(p, &flags);
for (t = next_thread(p); t != p; t = next_thread(t)) {
if (t->fs == p->fs)
@ -1073,11 +1075,19 @@ void check_unsafe_exec(struct linux_binprm *bprm)
n_sighand++;
}
if (atomic_read(&p->fs->count) > n_fs ||
atomic_read(&p->sighand->count) > n_sighand)
if (p->fs->users > n_fs ||
atomic_read(&p->sighand->count) > n_sighand) {
bprm->unsafe |= LSM_UNSAFE_SHARE;
} else {
if (p->fs->in_exec)
res = -EAGAIN;
p->fs->in_exec = 1;
}
unlock_task_sighand(p, &flags);
write_unlock(&p->fs->lock);
return res;
}
/*
@ -1296,12 +1306,15 @@ int do_execve(char * filename,
bprm->cred = prepare_exec_creds();
if (!bprm->cred)
goto out_unlock;
check_unsafe_exec(bprm);
retval = check_unsafe_exec(bprm);
if (retval)
goto out_unlock;
file = open_exec(filename);
retval = PTR_ERR(file);
if (IS_ERR(file))
goto out_unlock;
goto out_unmark;
sched_exec();
@ -1344,6 +1357,9 @@ int do_execve(char * filename,
goto out;
/* execve succeeded */
write_lock(&current->fs->lock);
current->fs->in_exec = 0;
write_unlock(&current->fs->lock);
current->in_execve = 0;
mutex_unlock(&current->cred_exec_mutex);
acct_update_integrals(current);
@ -1362,6 +1378,11 @@ out_file:
fput(bprm->file);
}
out_unmark:
write_lock(&current->fs->lock);
current->fs->in_exec = 0;
write_unlock(&current->fs->lock);
out_unlock:
current->in_execve = 0;
mutex_unlock(&current->cred_exec_mutex);

View file

@ -72,25 +72,27 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root)
path_put(old_root);
}
void put_fs_struct(struct fs_struct *fs)
void free_fs_struct(struct fs_struct *fs)
{
/* No need to hold fs->lock if we are killing it */
if (atomic_dec_and_test(&fs->count)) {
path_put(&fs->root);
path_put(&fs->pwd);
kmem_cache_free(fs_cachep, fs);
}
path_put(&fs->root);
path_put(&fs->pwd);
kmem_cache_free(fs_cachep, fs);
}
void exit_fs(struct task_struct *tsk)
{
struct fs_struct * fs = tsk->fs;
struct fs_struct *fs = tsk->fs;
if (fs) {
int kill;
task_lock(tsk);
write_lock(&fs->lock);
tsk->fs = NULL;
kill = !--fs->users;
write_unlock(&fs->lock);
task_unlock(tsk);
put_fs_struct(fs);
if (kill)
free_fs_struct(fs);
}
}
@ -99,7 +101,8 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
/* We don't need to lock fs - think why ;-) */
if (fs) {
atomic_set(&fs->count, 1);
fs->users = 1;
fs->in_exec = 0;
rwlock_init(&fs->lock);
fs->umask = old->umask;
read_lock(&old->lock);
@ -114,28 +117,54 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
int unshare_fs_struct(void)
{
struct fs_struct *fsp = copy_fs_struct(current->fs);
if (!fsp)
struct fs_struct *fs = current->fs;
struct fs_struct *new_fs = copy_fs_struct(fs);
int kill;
if (!new_fs)
return -ENOMEM;
exit_fs(current);
current->fs = fsp;
task_lock(current);
write_lock(&fs->lock);
kill = !--fs->users;
current->fs = new_fs;
write_unlock(&fs->lock);
task_unlock(current);
if (kill)
free_fs_struct(fs);
return 0;
}
EXPORT_SYMBOL_GPL(unshare_fs_struct);
/* to be mentioned only in INIT_TASK */
struct fs_struct init_fs = {
.count = ATOMIC_INIT(1),
.users = 1,
.lock = __RW_LOCK_UNLOCKED(init_fs.lock),
.umask = 0022,
};
void daemonize_fs_struct(void)
{
struct fs_struct *fs;
struct fs_struct *fs = current->fs;
exit_fs(current); /* current->fs->count--; */
fs = &init_fs;
current->fs = fs;
atomic_inc(&fs->count);
if (fs) {
int kill;
task_lock(current);
write_lock(&init_fs.lock);
init_fs.users++;
write_unlock(&init_fs.lock);
write_lock(&fs->lock);
current->fs = &init_fs;
kill = !--fs->users;
write_unlock(&fs->lock);
task_unlock(current);
if (kill)
free_fs_struct(fs);
}
}

View file

@ -44,7 +44,7 @@ extern void __init chrdev_init(void);
/*
* exec.c
*/
extern void check_unsafe_exec(struct linux_binprm *);
extern int check_unsafe_exec(struct linux_binprm *);
/*
* namespace.c

View file

@ -49,7 +49,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
else
bytes += kobjsize(mm);
if (current->fs && atomic_read(&current->fs->count) > 1)
if (current->fs && current->fs->users > 1)
sbytes += kobjsize(current->fs);
else
bytes += kobjsize(current->fs);

View file

@ -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);

View file

@ -683,11 +683,19 @@ fail_nomem:
static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
{
struct fs_struct *fs = current->fs;
if (clone_flags & CLONE_FS) {
atomic_inc(&current->fs->count);
/* tsk->fs is already what we want */
write_lock(&fs->lock);
if (fs->in_exec) {
write_unlock(&fs->lock);
return -EAGAIN;
}
fs->users++;
write_unlock(&fs->lock);
return 0;
}
tsk->fs = copy_fs_struct(current->fs);
tsk->fs = copy_fs_struct(fs);
if (!tsk->fs)
return -ENOMEM;
return 0;
@ -1518,12 +1526,16 @@ static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
{
struct fs_struct *fs = current->fs;
if ((unshare_flags & CLONE_FS) &&
(fs && atomic_read(&fs->count) > 1)) {
*new_fsp = copy_fs_struct(current->fs);
if (!*new_fsp)
return -ENOMEM;
}
if (!(unshare_flags & CLONE_FS) || !fs)
return 0;
/* don't need lock here; in the worst case we'll do useless copy */
if (fs->users == 1)
return 0;
*new_fsp = copy_fs_struct(fs);
if (!*new_fsp)
return -ENOMEM;
return 0;
}
@ -1639,8 +1651,13 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
if (new_fs) {
fs = current->fs;
write_lock(&fs->lock);
current->fs = new_fs;
new_fs = fs;
if (--fs->users)
new_fs = NULL;
else
new_fs = fs;
write_unlock(&fs->lock);
}
if (new_mm) {
@ -1679,7 +1696,7 @@ bad_unshare_cleanup_sigh:
bad_unshare_cleanup_fs:
if (new_fs)
put_fs_struct(new_fs);
free_fs_struct(new_fs);
bad_unshare_cleanup_thread:
bad_unshare_out: