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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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31
fs/exec.c
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@ -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);