[PATCH 04/11] vfs: add missing checks to copy_file_range

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

Like the clone and dedupe interfaces we've recently fixed, the
copy_file_range() implementation is missing basic sanity, limits and
boundary condition tests on the parameters that are passed to it
from userspace. Create a new "generic_copy_file_checks()" function
modelled on the generic_remap_checks() function to provide this
missing functionality.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/read_write.c    | 27 ++++++------------
 include/linux/fs.h |  3 ++
 mm/filemap.c       | 69 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+), 18 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 44339b44accc..69809345977e 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1578,7 +1578,7 @@ static ssize_t do_copy_file_range(struct file *file_in, loff_t pos_in,
 		return file_out->f_op->copy_file_range(file_in, pos_in, file_out,
 						      pos_out, len, flags);
 
-	return generic_copy_file_range(file_in, &pos_in, file_out, &pos_out,
+	return generic_copy_file_range(file_in, pos_in, file_out, pos_out,
 					len, flags);
 }
 
@@ -1598,10 +1598,14 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 	if (flags != 0)
 		return -EINVAL;
 
-	if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))
-		return -EISDIR;
-	if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
-		return -EINVAL;
+	/* this could be relaxed once a method supports cross-fs copies */
+	if (inode_in->i_sb != inode_out->i_sb)
+		return -EXDEV;
+
+	ret = generic_copy_file_checks(file_in, pos_in, file_out, pos_out, &len,
+					flags);
+	if (ret < 0)
+		return ret;
 
 	ret = rw_verify_area(READ, file_in, &pos_in, len);
 	if (unlikely(ret))
@@ -1611,22 +1615,9 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 	if (unlikely(ret))
 		return ret;
 
-	if (!(file_in->f_mode & FMODE_READ) ||
-	    !(file_out->f_mode & FMODE_WRITE) ||
-	    (file_out->f_flags & O_APPEND))
-		return -EBADF;
-
-	/* this could be relaxed once a method supports cross-fs copies */
-	if (inode_in->i_sb != inode_out->i_sb)
-		return -EXDEV;
-
 	if (len == 0)
 		return 0;
 
-	/* If the source range crosses EOF, fail the copy */
-	if (pos_in >= i_size(inode_in) || pos_in + len > i_size(inode_in))
-		return -EINVAL;
-
 	file_start_write(file_out);
 
 	/*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a4478764cf63..0d9d2d93d4df 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3022,6 +3022,9 @@ extern ssize_t generic_write_checks(struct kiocb *, struct iov_iter *);
 extern int generic_remap_checks(struct file *file_in, loff_t pos_in,
 				struct file *file_out, loff_t pos_out,
 				loff_t *count, unsigned int remap_flags);
+extern int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
+				struct file *file_out, loff_t pos_out,
+				size_t *count, unsigned int flags);
 extern ssize_t generic_file_read_iter(struct kiocb *, struct iov_iter *);
 extern ssize_t __generic_file_write_iter(struct kiocb *, struct iov_iter *);
 extern ssize_t generic_file_write_iter(struct kiocb *, struct iov_iter *);
diff --git a/mm/filemap.c b/mm/filemap.c
index 81adec8ee02c..0a170425935b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2975,6 +2975,75 @@ int generic_remap_checks(struct file *file_in, loff_t pos_in,
 	return 0;
 }
 
+
+/*
+ * Performs necessary checks before doing a file copy
+ *
+ * Can adjust amount of bytes to copy
+ * Returns appropriate error code that caller should return or
+ * zero in case the copy should be allowed.
+ */
+int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
+			 struct file *file_out, loff_t pos_out,
+			 size_t *req_count, unsigned int flags)
+{
+	struct inode *inode_in = file_inode(file_in);
+	struct inode *inode_out = file_inode(file_out);
+	uint64_t count = *req_count;
+	uint64_t bcount;
+	loff_t size_in, size_out;
+	loff_t bs = inode_out->i_sb->s_blocksize;
+	int ret;
+
+	/* Don't touch certain kinds of inodes */
+	if (IS_IMMUTABLE(inode_out))
+		return -EPERM;
+
+	if (IS_SWAPFILE(inode_in) || IS_SWAPFILE(inode_out))
+		return -ETXTBSY;
+
+	/* Don't copy dirs, pipes, sockets... */
+	if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))
+		return -EISDIR;
+	if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
+		return -EINVAL;
+
+	if (!(file_in->f_mode & FMODE_READ) ||
+	    !(file_out->f_mode & FMODE_WRITE) ||
+	    (file_out->f_flags & O_APPEND))
+		return -EBADF;
+
+	/* Ensure offsets don't wrap. */
+	if (pos_in + count < pos_in || pos_out + count < pos_out)
+		return -EOVERFLOW;
+
+	size_in = i_size_read(inode_in);
+	size_out = i_size_read(inode_out);
+
+	/* If the source range crosses EOF, fail the copy */
+	if (pos_in >= size_in)
+		return -EINVAL;
+	if (pos_in + count > size_in)
+		return -EINVAL;
+
+	ret = generic_access_check_limits(file_in, pos_in, &count);
+	if (ret)
+		return ret;
+
+	ret = generic_write_check_limits(file_out, pos_out, &count);
+	if (ret)
+		return ret;
+
+	/* Don't allow overlapped copying within the same file. */
+	if (inode_in == inode_out &&
+	    pos_out + count > pos_in &&
+	    pos_out < pos_in + count)
+		return -EINVAL;
+
+	*req_count = count;
+	return 0;
+}
+
 int pagecache_write_begin(struct file *file, struct address_space *mapping,
 				loff_t pos, unsigned len, unsigned flags,
 				struct page **pagep, void **fsdata)
-- 
2.19.1