fix mremap() vs. ioctx_kill() race

teach ->mremap() method to return an error and have it fail for
aio mappings in process of being killed

Note that in case of ->mremap() failure we need to undo move_page_tables()
we'd already done; we could call ->mremap() first, but then the failure of
move_page_tables() would require undoing whatever _successful_ ->mremap()
has done, which would be a lot more headache in general.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/aio.c b/fs/aio.c
index f8e52a1..58c33dc 100644 (file)
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -278,11 +278,11 @@ static int aio_ring_mmap(struct file *file, struct vm_area_struct *vma)
        return 0;
 }
 
-static void aio_ring_remap(struct file *file, struct vm_area_struct *vma)
+static int aio_ring_remap(struct file *file, struct vm_area_struct *vma)
 {
        struct mm_struct *mm = vma->vm_mm;
        struct kioctx_table *table;
-       int i;
+       int i, res = -EINVAL;
 
        spin_lock(&mm->ioctx_lock);
        rcu_read_lock();
@@ -292,13 +292,17 @@ static void aio_ring_remap(struct file *file, struct vm_area_struct *vma)
 
                ctx = table->table[i];
                if (ctx && ctx->aio_ring_file == file) {
-                       ctx->user_id = ctx->mmap_base = vma->vm_start;
+                       if (!atomic_read(&ctx->dead)) {
+                               ctx->user_id = ctx->mmap_base = vma->vm_start;
+                               res = 0;
+                       }
                        break;
                }
        }
 
        rcu_read_unlock();
        spin_unlock(&mm->ioctx_lock);
+       return res;
 }
 
 static const struct file_operations aio_ring_fops = {
@@ -748,11 +752,12 @@ static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
 {
        struct kioctx_table *table;
 
-       if (atomic_xchg(&ctx->dead, 1))
+       spin_lock(&mm->ioctx_lock);
+       if (atomic_xchg(&ctx->dead, 1)) {
+               spin_unlock(&mm->ioctx_lock);
                return -EINVAL;
+       }
 
-
-       spin_lock(&mm->ioctx_lock);
        table = rcu_dereference_raw(mm->ioctx_table);
        WARN_ON(ctx != table->table[ctx->id]);
        table->table[ctx->id] = NULL;

diff --git a/include/linux/fs.h b/include/linux/fs.h
index f4131e8..52cc449 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1549,7 +1549,7 @@ struct file_operations {
        long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
        long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
        int (*mmap) (struct file *, struct vm_area_struct *);
-       void (*mremap)(struct file *, struct vm_area_struct *);
+       int (*mremap)(struct file *, struct vm_area_struct *);
        int (*open) (struct inode *, struct file *);
        int (*flush) (struct file *, fl_owner_t id);
        int (*release) (struct inode *, struct file *);

diff --git a/mm/mremap.c b/mm/mremap.c
index 57dadc0..2dc44b1 100644 (file)
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -286,8 +286,14 @@ static unsigned long move_vma(struct vm_area_struct *vma,
                old_len = new_len;
                old_addr = new_addr;
                new_addr = -ENOMEM;
-       } else if (vma->vm_file && vma->vm_file->f_op->mremap)
-               vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
+       } else if (vma->vm_file && vma->vm_file->f_op->mremap) {
+               err = vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
+               if (err < 0) {
+                       move_page_tables(new_vma, new_addr, vma, old_addr,
+                                        moved_len, true);
+                       return err;
+               }
+       }
 
        /* Conceal VM_ACCOUNT so old reservation is not undone */
        if (vm_flags & VM_ACCOUNT) {