vfs: add missing checks to copy_file_range

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.

[Amir] Shorten copy length instead of checking pos_in limits
because input file size already abides by the limits.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

3 files changed, 58 insertions, 1 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index f1900bdb3127..b0fb1176b628 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1626,7 +1626,8 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
         if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
                 return -EXDEV;
 
-        ret = generic_file_rw_checks(file_in, file_out);
+        ret = generic_copy_file_checks(file_in, pos_in, file_out, pos_out, &len,
+                                       flags);
         if (unlikely(ret))
                 return ret;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 89b9b73eb581..e4d382c4342a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3050,6 +3050,9 @@ 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_file_rw_checks(struct file *file_in, struct file *file_out);
+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 44361928bbb0..aac71aef4c61 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3056,6 +3056,59 @@ int generic_file_rw_checks(struct file *file_in, struct file *file_out)
         return 0;
 }
 
+/*
+ * Performs necessary checks before doing a file copy
+ *
+ * Can adjust amount of bytes to copy via @req_count argument.
+ * 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;
+        loff_t size_in;
+        int ret;
+
+        ret = generic_file_rw_checks(file_in, file_out);
+        if (ret)
+                return 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;
+
+        /* Ensure offsets don't wrap. */
+        if (pos_in + count < pos_in || pos_out + count < pos_out)
+                return -EOVERFLOW;
+
+        /* Shorten the copy to EOF */
+        size_in = i_size_read(inode_in);
+        if (pos_in >= size_in)
+                count = 0;
+        else
+                count = min(count, size_in - (uint64_t)pos_in);
+
+        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)