[PATCH 04/91] agp: fix arbitrary kernel memory writes

[Willy Tarreau]

2.6.27-longterm review patch.  If anyone has any objections, please let us know.

------------------

commit 194b3da873fd334ef183806db751473512af29ce upstream.

pg_start is copied from userspace on AGPIOC_BIND and AGPIOC_UNBIND ioctl
cmds of agp_ioctl() and passed to agpioc_bind_wrap().  As said in the
comment, (pg_start + mem->page_count) may wrap in case of AGPIOC_BIND,
and it is not checked at all in case of AGPIOC_UNBIND.  As a result, user
with sufficient privileges (usually "video" group) may generate either
local DoS or privilege escalation.

Signed-off-by: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>
Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
 drivers/char/agp/generic.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

Index: longterm-2.6.27/drivers/char/agp/generic.c
===================================================================
--- longterm-2.6.27.orig/drivers/char/agp/generic.c	2012-02-05 22:34:34.961915038 +0100
+++ longterm-2.6.27/drivers/char/agp/generic.c	2012-02-05 22:34:35.500916106 +0100
@@ -1099,8 +1099,8 @@
 		return -EINVAL;
 	}
 
-	/* AK: could wrap */
-	if ((pg_start + mem->page_count) > num_entries)
+	if (((pg_start + mem->page_count) > num_entries) ||
+	    ((pg_start + mem->page_count) < pg_start))
 		return -EINVAL;
 
 	j = pg_start;
@@ -1132,7 +1132,7 @@
 {
 	size_t i;
 	struct agp_bridge_data *bridge;
-	int mask_type;
+	int mask_type, num_entries;
 
 	bridge = mem->bridge;
 	if (!bridge)
@@ -1144,6 +1144,11 @@
 	if (type != mem->type)
 		return -EINVAL;
 
+	num_entries = agp_num_entries();
+	if (((pg_start + mem->page_count) > num_entries) ||
+	    ((pg_start + mem->page_count) < pg_start))
+		return -EINVAL;
+
 	mask_type = bridge->driver->agp_type_to_mask_type(bridge, type);
 	if (mask_type != 0) {
 		/* The generic routines know nothing of memory types */


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