linux-kernel - [PATCH v4 10/12] binfmt_flat: update libraries' data segment pointer with userspace accessors

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Message-Id: <1469042561-7360-11-git-send-email-nicolas.pitre@linaro.org>
Date:	Wed, 20 Jul 2016 15:22:39 -0400
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Greg Ungerer <gerg@...ux-m68k.org>
Subject: [PATCH v4 10/12] binfmt_flat: update libraries' data segment pointer with userspace accessors

This is needed on systems with a MMU.  This also gets rid of the
strangest C code I've seen lateli i.e. an integer indexed with a
pointer value within square brackets. That really looked backwards.

Signed-off-by: Nicolas Pitre <nico@...aro.org>
Reviewed-by: Greg Ungerer <gerg@...ux-m68k.org>
---
 fs/binfmt_flat.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
index 92c1530a2c..aa7971ce6a 100644
--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -894,12 +894,19 @@ static int load_flat_binary(struct linux_binprm *bprm)
 		return res;
 
 	/* Update data segment pointers for all libraries */
-	for (i = 0; i < MAX_SHARED_LIBS; i++)
-		if (libinfo.lib_list[i].loaded)
-			for (j = 0; j < MAX_SHARED_LIBS; j++)
-				(-(j+1))[(unsigned long *)(libinfo.lib_list[i].start_data)] =
-					(libinfo.lib_list[j].loaded) ?
-						libinfo.lib_list[j].start_data : UNLOADED_LIB;
+	for (i = 0; i < MAX_SHARED_LIBS; i++) {
+		if (!libinfo.lib_list[i].loaded)
+			continue;
+		for (j = 0; j < MAX_SHARED_LIBS; j++) {
+			unsigned long val = libinfo.lib_list[j].loaded ?
+				libinfo.lib_list[j].start_data : UNLOADED_LIB;
+			unsigned long __user *p = (unsigned long __user *)
+				libinfo.lib_list[i].start_data;
+			p -= j + 1;
+			if (put_user(val, p))
+				return -EFAULT;
+		}
+	}
 
 	install_exec_creds(bprm);
 
-- 
2.7.4