UBIFS: Fix potential integer overflow in allocation

BugLink: https://bugs.launchpad.net/bugs/1784382

commit 353748a3 upstream.

There is potential for the size and len fields in ubifs_data_node to be
too large causing either a negative value for the length fields or an
integer overflow leading to an incorrect memory allocation. Likewise,
when the len field is small, an integer underflow may occur.
Signed-off-by: Silvio Cesare <silvio.cesare@gmail.com>
Fixes: 1e51764a ("UBIFS: add new flash file system")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

fs/ubifs/journal.c

@@ -1107,7 +1107,7 @@ static int recomp_data_node(const struct ubifs_info *c,
 	int err, len, compr_type, out_len;
 
 	out_len = le32_to_cpu(dn->size);
-	buf = kmalloc(out_len * WORST_COMPR_FACTOR, GFP_NOFS);
+	buf = kmalloc_array(out_len, WORST_COMPR_FACTOR, GFP_NOFS);
 	if (!buf)
 		return -ENOMEM;