Re: [patch] mlock-as-nonroot revisted

From: Rik van Riel
Date: Tue Aug 03 2004 - 16:00:18 EST

On Thu, 29 Jul 2004, Chris Wright wrote:

> 1) hugetlb accounting is not done. so it's only simple change to checking
> permission, but the acutal usage is not tracked

This patch should fix that. It's incremental with Arjan's
patch and the "set shp->mlock_user" patch I just sent.

Are you ok with how this is implemented ?

Please shoot holes in it, so I can make this better... ;)

--- linux-2.6.7/include/linux/mm.h.htlb 2004-08-03 16:29:07.362393143 -0400
+++ linux-2.6.7/include/linux/mm.h 2004-08-03 16:31:20.179095875 -0400
@@ -509,7 +509,8 @@
return 1;
return 0;
}
-
+extern int user_can_mlock(size_t, struct user_struct *);
+extern void user_subtract_mlock(size_t, struct user_struct *);

/*
* Parameter block passed down to zap_pte_range in exceptional cases.
--- linux-2.6.7/fs/hugetlbfs/inode.c.htlb 2004-08-03 13:33:26.433750664 -0400
+++ linux-2.6.7/fs/hugetlbfs/inode.c 2004-08-03 14:08:43.636761209 -0400
@@ -718,7 +718,7 @@

struct file *hugetlb_zero_setup(size_t size)
{
- int error;
+ int error = -ENOMEM;
struct file *file;
struct inode *inode;
struct dentry *dentry, *root;
@@ -731,6 +731,9 @@
if (!is_hugepage_mem_enough(size))
return ERR_PTR(-ENOMEM);

+ if (!user_can_mlock(size, current->user))
+ return ERR_PTR(-ENOMEM);
+
root = hugetlbfs_vfsmount->mnt_root;
snprintf(buf, 16, "%lu", hugetlbfs_counter());
quick_string.name = buf;
@@ -738,7 +741,7 @@
quick_string.hash = 0;
dentry = d_alloc(root, &quick_string);
if (!dentry)
- return ERR_PTR(-ENOMEM);
+ goto out_subtract_mlock;

error = -ENFILE;
file = get_empty_filp();
@@ -765,6 +768,8 @@
put_filp(file);
out_dentry:
dput(dentry);
+out_subtract_mlock:
+ user_subtract_mlock(size, current->user);
return ERR_PTR(error);
}

--- linux-2.6.7/ipc/shm.c.htlb 2004-08-03 11:46:08.383363603 -0400
+++ linux-2.6.7/ipc/shm.c 2004-08-03 16:48:26.150674657 -0400
@@ -115,6 +115,9 @@
shm_unlock(shp);
if (!is_file_hugepages(shp->shm_file))
shmem_lock(shp->shm_file, 0, shp->mlock_user);
+ else
+ user_subtract_mlock(shp->shm_file->f_dentry->d_inode->i_size,
+ shp->mlock_user);
fput (shp->shm_file);
security_shm_free(shp);
ipc_rcu_free(shp, sizeof(struct shmid_kernel));
@@ -198,9 +201,11 @@
return error;
}

- if (shmflg & SHM_HUGETLB)
+ if (shmflg & SHM_HUGETLB) {
+ /* hugetlb_zero_setup takes care of mlock user accounting */
file = hugetlb_zero_setup(size);
- else {
+ shp->mlock_user = current->user;
+ } else {
sprintf (name, "SYSV%08x", key);
file = shmem_file_setup(name, size, VM_ACCOUNT);
}
--- linux-2.6.7/mm/shmem.c.htlb 2004-08-03 14:08:49.277094888 -0400
+++ linux-2.6.7/mm/shmem.c 2004-08-03 16:32:41.215119384 -0400
@@ -1151,41 +1151,27 @@
}
#endif

-/* Protects current->user->locked_shm from concurrent access */
-static spinlock_t shmem_lock_user = SPIN_LOCK_UNLOCKED;
-
int shmem_lock(struct file *file, int lock, struct user_struct * user)
{
struct inode *inode = file->f_dentry->d_inode;
struct shmem_inode_info *info = SHMEM_I(inode);
- unsigned long lock_limit, locked;
int retval = -ENOMEM;

+ if (!can_do_mlock())
+ return -EPERM;
+
spin_lock(&info->lock);
- spin_lock(&shmem_lock_user);
if (lock && !(info->flags & VM_LOCKED)) {
- locked = inode->i_size >> PAGE_SHIFT;
- locked += user->locked_shm;
- lock_limit = current->rlim[RLIMIT_MEMLOCK].rlim_cur;
- lock_limit >>= PAGE_SHIFT;
- if ((locked > lock_limit) && !capable(CAP_IPC_LOCK))
+ if (!user_can_mlock(inode->i_size, user) && !capable(CAP_IPC_LOCK))
goto out_nomem;
- /* for this branch user == current->user so it won't go away under us */
- atomic_inc(&user->__count);
- user->locked_shm = locked;
+ info->flags |= VM_LOCKED;
}
if (!lock && (info->flags & VM_LOCKED) && user) {
- locked = inode->i_size >> PAGE_SHIFT;
- user->locked_shm -= locked;
- free_uid(user);
- }
- if (lock)
- info->flags |= VM_LOCKED;
- else
+ user_subtract_mlock(inode->i_size, user);
info->flags &= ~VM_LOCKED;
+ }
retval = 0;
out_nomem:
- spin_unlock(&shmem_lock_user);
spin_unlock(&info->lock);
return retval;
}
--- linux-2.6.7/mm/mlock.c.htlb 2004-08-03 14:27:35.270370974 -0400
+++ linux-2.6.7/mm/mlock.c 2004-08-03 16:32:05.650641994 -0400
@@ -193,3 +193,38 @@
up_write(&current->mm->mmap_sem);
return ret;
}
+
+/*
+ * Objects with different lifetime than processes (mlocked shm segments
+ * and hugetlb files) get accounted against the user_struct instead.
+ */
+static spinlock_t mlock_user_lock = SPIN_LOCK_UNLOCKED;
+
+int user_can_mlock(size_t size, struct user_struct * user)
+{
+ unsigned long lock_limit, locked;
+ int allowed = 0;
+
+ spin_lock(&mlock_user_lock);
+ locked = size >> PAGE_SHIFT;
+ lock_limit = current->rlim[RLIMIT_MEMLOCK].rlim_cur;
+ lock_limit >>= PAGE_SHIFT;
+ if (locked + user->locked_shm > lock_limit)
+ goto out;
+ atomic_inc(&user->__count);
+ user->locked_shm += locked;
+ allowed = 1;
+out:
+ spin_unlock(&mlock_user_lock);
+ return allowed;
+}
+
+void user_subtract_mlock(size_t size, struct user_struct * user)
+{
+ if (user) {
+ spin_lock(&mlock_user_lock);
+ user->locked_shm -= (size >> PAGE_SHIFT);
+ spin_unlock(&mlock_user_lock);
+ free_uid(user);
+ }
+}

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