fs/ntfs3: Do copy_to_user out of run_lock

In order not to call copy_to_user (from fiemap_fill_next_extent)
we allocate memory in the kernel, fill it and copy it to user memory
after up_read(run_lock).

Reported-by: syzbot+36bb70085ef6edc2ebb9@syzkaller.appspotmail.com
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

fs/ntfs3/frecord.c

@@ -1898,6 +1898,47 @@ enum REPARSE_SIGN ni_parse_reparse(struct ntfs_inode *ni, struct ATTRIB *attr,
 	return REPARSE_LINK;
 }
 
+/*
+ * fiemap_fill_next_extent_k - a copy of fiemap_fill_next_extent
+ * but it accepts kernel address for fi_extents_start
+ */
+static int fiemap_fill_next_extent_k(struct fiemap_extent_info *fieinfo,
+				     u64 logical, u64 phys, u64 len, u32 flags)
+{
+	struct fiemap_extent extent;
+	struct fiemap_extent __user *dest = fieinfo->fi_extents_start;
+
+	/* only count the extents */
+	if (fieinfo->fi_extents_max == 0) {
+		fieinfo->fi_extents_mapped++;
+		return (flags & FIEMAP_EXTENT_LAST) ? 1 : 0;
+	}
+
+	if (fieinfo->fi_extents_mapped >= fieinfo->fi_extents_max)
+		return 1;
+
+	if (flags & FIEMAP_EXTENT_DELALLOC)
+		flags |= FIEMAP_EXTENT_UNKNOWN;
+	if (flags & FIEMAP_EXTENT_DATA_ENCRYPTED)
+		flags |= FIEMAP_EXTENT_ENCODED;
+	if (flags & (FIEMAP_EXTENT_DATA_TAIL | FIEMAP_EXTENT_DATA_INLINE))
+		flags |= FIEMAP_EXTENT_NOT_ALIGNED;
+
+	memset(&extent, 0, sizeof(extent));
+	extent.fe_logical = logical;
+	extent.fe_physical = phys;
+	extent.fe_length = len;
+	extent.fe_flags = flags;
+
+	dest += fieinfo->fi_extents_mapped;
+	memcpy(dest, &extent, sizeof(extent));
+
+	fieinfo->fi_extents_mapped++;
+	if (fieinfo->fi_extents_mapped == fieinfo->fi_extents_max)
+		return 1;
+	return (flags & FIEMAP_EXTENT_LAST) ? 1 : 0;
+}
+
 /*
  * ni_fiemap - Helper for file_fiemap().
  *
@@ -1908,6 +1949,8 @@ int ni_fiemap(struct ntfs_inode *ni, struct fiemap_extent_info *fieinfo,
 	      __u64 vbo, __u64 len)
 {
 	int err = 0;
+	struct fiemap_extent __user *fe_u = fieinfo->fi_extents_start;
+	struct fiemap_extent *fe_k = NULL;
 	struct ntfs_sb_info *sbi = ni->mi.sbi;
 	u8 cluster_bits = sbi->cluster_bits;
 	struct runs_tree *run;
@@ -1955,6 +1998,18 @@ int ni_fiemap(struct ntfs_inode *ni, struct fiemap_extent_info *fieinfo,
 		goto out;
 	}
 
+	/*
+	 * To avoid lock problems replace pointer to user memory by pointer to kernel memory.
+	 */
+	fe_k = kmalloc_array(fieinfo->fi_extents_max,
+			     sizeof(struct fiemap_extent),
+			     GFP_NOFS | __GFP_ZERO);
+	if (!fe_k) {
+		err = -ENOMEM;
+		goto out;
+	}
+	fieinfo->fi_extents_start = fe_k;
+
 	end = vbo + len;
 	alloc_size = le64_to_cpu(attr->nres.alloc_size);
 	if (end > alloc_size)
@@ -2043,8 +2098,9 @@ int ni_fiemap(struct ntfs_inode *ni, struct fiemap_extent_info *fieinfo,
 			if (vbo + dlen >= end)
 				flags |= FIEMAP_EXTENT_LAST;
 
-			err = fiemap_fill_next_extent(fieinfo, vbo, lbo, dlen,
-						      flags);
+			err = fiemap_fill_next_extent_k(fieinfo, vbo, lbo, dlen,
+							flags);
+
 			if (err < 0)
 				break;
 			if (err == 1) {
@@ -2064,7 +2120,8 @@ int ni_fiemap(struct ntfs_inode *ni, struct fiemap_extent_info *fieinfo,
 		if (vbo + bytes >= end)
 			flags |= FIEMAP_EXTENT_LAST;
 
-		err = fiemap_fill_next_extent(fieinfo, vbo, lbo, bytes, flags);
+		err = fiemap_fill_next_extent_k(fieinfo, vbo, lbo, bytes,
+						flags);
 		if (err < 0)
 			break;
 		if (err == 1) {
@@ -2077,7 +2134,19 @@ int ni_fiemap(struct ntfs_inode *ni, struct fiemap_extent_info *fieinfo,
 
 	up_read(run_lock);
 
+	/*
+	 * Copy to user memory out of lock
+	 */
+	if (copy_to_user(fe_u, fe_k,
+			 fieinfo->fi_extents_max *
+				 sizeof(struct fiemap_extent))) {
+		err = -EFAULT;
+	}
+
 out:
+	/* Restore original pointer. */
+	fieinfo->fi_extents_start = fe_u;
+	kfree(fe_k);
 	return err;
 }