cifs: Fix integer overflow while processing acregmax mount option

User-provided mount parameter acregmax of type u32 is intended to have
an upper limit, but before it is validated, the value is converted from
seconds to jiffies which can lead to an integer overflow.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 5780464 ("cifs: Add new parameter "acregmax" for distinct file and directory metadata timeout")
Signed-off-by: Murad Masimov <m.masimov@mt-integration.ru>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Murad Masimov

fs/smb/client/fs_context.c

@@ -1344,11 +1344,11 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
 		}
 		break;
 	case Opt_acregmax:
-		ctx->acregmax = HZ * result.uint_32;
-		if (ctx->acregmax > CIFS_MAX_ACTIMEO) {
+		if (result.uint_32 > CIFS_MAX_ACTIMEO / HZ) {
 			cifs_errorf(fc, "acregmax too large\n");
 			goto cifs_parse_mount_err;
 		}
+		ctx->acregmax = HZ * result.uint_32;
 		break;
 	case Opt_acdirmax:
 		ctx->acdirmax = HZ * result.uint_32;