[PATCH 05/91] agp: fix OOM and buffer overflow

From: Willy Tarreau
Date: Sun Feb 05 2012 - 17:44:52 EST

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


commit b522f02184b413955f3bc952e3776ce41edc6355 upstream.

page_count is copied from userspace. agp_allocate_memory() tries to
check whether this number is too big, but doesn't take into account the
wrap case. Also agp_create_user_memory() doesn't check whether
alloc_size is calculated from num_agp_pages variable without overflow.
This may lead to allocation of too small buffer with following buffer

Another problem in agp code is not addressed in the patch - kernel memory
exhaustion (AGPIOC_RESERVE and AGPIOC_ALLOCATE ioctls). It is not checked
whether requested pid is a pid of the caller (no check in agpioc_reserve_wrap()).
Each allocation is limited to 16KB, though, there is no per-process limit.
This might lead to OOM situation, which is not even solved in case of the
caller death by OOM killer - the memory is allocated for another (faked) process.

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 | 8 +++++++-
1 files changed, 7 insertions(+), 1 deletions(-)

Index: longterm-2.6.27/drivers/char/agp/generic.c
--- longterm-2.6.27.orig/drivers/char/agp/generic.c 2012-02-05 22:34:35.500916106 +0100
+++ longterm-2.6.27/drivers/char/agp/generic.c 2012-02-05 22:34:35.639914999 +0100
@@ -123,6 +123,9 @@
struct agp_memory *new;
unsigned long alloc_size = num_agp_pages*sizeof(struct page *);

+ if (INT_MAX/sizeof(struct page *) < num_agp_pages)
+ return NULL;
new = kzalloc(sizeof(struct agp_memory), GFP_KERNEL);
if (new == NULL)
return NULL;
@@ -236,11 +239,14 @@
int scratch_pages;
struct agp_memory *new;
size_t i;
+ int cur_memory;

if (!bridge)
return NULL;

- if ((atomic_read(&bridge->current_memory_agp) + page_count) > bridge->max_memory_agp)
+ cur_memory = atomic_read(&bridge->current_memory_agp);
+ if ((cur_memory + page_count > bridge->max_memory_agp) ||
+ (cur_memory + page_count < page_count))
return NULL;

if (type >= AGP_USER_TYPES) {

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