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Subject[PATCH 02/21] platform: goldfish: pipe: Prevent memory corruption from several threads writing to the same variable
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From: Roman Kiryanov <rkir@google.com>

Move the "pages" buffer into "struct goldfish_pipe". Since we are
locking the mutex on the pipe in transfer_max_buffers, other threads
willnot be able to write into it, but other pipe instances could be
served because they have its own buffer.

Signed-off-by: Roman Kiryanov <rkir@google.com>
---
drivers/platform/goldfish/goldfish_pipe.c | 24 +++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/drivers/platform/goldfish/goldfish_pipe.c b/drivers/platform/goldfish/goldfish_pipe.c
index b4a484bbcdaa..6ae2b00f4bff 100644
--- a/drivers/platform/goldfish/goldfish_pipe.c
+++ b/drivers/platform/goldfish/goldfish_pipe.c
@@ -163,6 +163,9 @@ struct goldfish_pipe {

/* Pointer to the parent goldfish_pipe_dev instance */
struct goldfish_pipe_dev *dev;
+
+ /* A buffer of pages, too large to fit into a stack frame */
+ struct page *pages[MAX_BUFFERS_PER_COMMAND];
};

/* The global driver data. Holds a reference to the i/o page used to
@@ -340,21 +343,23 @@ static int transfer_max_buffers(struct goldfish_pipe *pipe,
s32 *consumed_size,
int *status)
{
- static struct page *pages[MAX_BUFFERS_PER_COMMAND];
unsigned long first_page = address & PAGE_MASK;
unsigned int iter_last_page_size;
- int pages_count = pin_user_pages(first_page, last_page,
- last_page_size, is_write,
- pages, &iter_last_page_size);
-
- if (pages_count < 0)
- return pages_count;
+ int pages_count;

/* Serialize access to the pipe command buffers */
if (mutex_lock_interruptible(&pipe->lock))
return -ERESTARTSYS;

- populate_rw_params(pages, pages_count, address, address_end,
+ pages_count = pin_user_pages(first_page, last_page,
+ last_page_size, is_write,
+ pipe->pages, &iter_last_page_size);
+ if (pages_count < 0) {
+ mutex_unlock(&pipe->lock);
+ return pages_count;
+ }
+
+ populate_rw_params(pipe->pages, pages_count, address, address_end,
first_page, last_page, iter_last_page_size, is_write,
pipe->command_buffer);

@@ -364,10 +369,9 @@ static int transfer_max_buffers(struct goldfish_pipe *pipe,

*consumed_size = pipe->command_buffer->rw_params.consumed_size;

- release_user_pages(pages, pages_count, is_write, *consumed_size);
+ release_user_pages(pipe->pages, pages_count, is_write, *consumed_size);

mutex_unlock(&pipe->lock);
-
return 0;
}

--
2.19.0.397.gdd90340f6a-goog
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