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>
diff --git a/fs/compat.c b/fs/compat.c
index 55efdfe..baabf20 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -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 @@
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 @@
goto out;
/* execve succeeded */
+ write_lock(¤t->fs->lock);
+ current->fs->in_exec = 0;
+ write_unlock(¤t->fs->lock);
current->in_execve = 0;
mutex_unlock(¤t->cred_exec_mutex);
acct_update_integrals(current);
@@ -1506,6 +1513,11 @@
fput(bprm->file);
}
+out_unmark:
+ write_lock(¤t->fs->lock);
+ current->fs->in_exec = 0;
+ write_unlock(¤t->fs->lock);
+
out_unlock:
current->in_execve = 0;
mutex_unlock(¤t->cred_exec_mutex);
diff --git a/fs/exec.c b/fs/exec.c
index c5128fb..07a0596 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1056,16 +1056,18 @@
* - 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 @@
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 @@
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 @@
goto out;
/* execve succeeded */
+ write_lock(¤t->fs->lock);
+ current->fs->in_exec = 0;
+ write_unlock(¤t->fs->lock);
current->in_execve = 0;
mutex_unlock(¤t->cred_exec_mutex);
acct_update_integrals(current);
@@ -1362,6 +1378,11 @@
fput(bprm->file);
}
+out_unmark:
+ write_lock(¤t->fs->lock);
+ current->fs->in_exec = 0;
+ write_unlock(¤t->fs->lock);
+
out_unlock:
current->in_execve = 0;
mutex_unlock(¤t->cred_exec_mutex);
diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index 36e0a12..41cff72 100644
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -72,25 +72,27 @@
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 *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 @@
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);
+ }
}
diff --git a/fs/internal.h b/fs/internal.h
index 477a105f..b4dac4f 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -44,7 +44,7 @@
/*
* exec.c
*/
-extern void check_unsafe_exec(struct linux_binprm *);
+extern int check_unsafe_exec(struct linux_binprm *);
/*
* namespace.c
diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 343ea12..6ca0105 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -49,7 +49,7 @@
else
bytes += kobjsize(mm);
- if (current->fs && atomic_read(¤t->fs->count) > 1)
+ if (current->fs && current->fs->users > 1)
sbytes += kobjsize(current->fs);
else
bytes += kobjsize(current->fs);
