[PATCH 3.16 240/366] ibmasm: don't write out of bounds in read handler

Ben Hutchings
2018-11-12T05:48:13Z

From: Jann Horn <jannh@google.com>

commit a0341fc1981a950c1e902ab901e98f60e0e243f3 upstream.

This read handler had a lot of custom logic and wrote outside the bounds of
the provided buffer. This could lead to kernel and userspace memory
corruption. Just use simple_read_from_buffer() with a stack buffer.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/misc/ibmasm/ibmasmfs.c | 27 +++------------------------
1 file changed, 3 insertions(+), 24 deletions(-)

--- a/drivers/misc/ibmasm/ibmasmfs.c
+++ b/drivers/misc/ibmasm/ibmasmfs.c
@@ -507,35 +507,14 @@ static int remote_settings_file_close(st
static ssize_t remote_settings_file_read(struct file *file, char __user *buf, size_t count, loff_t *offset)
{
void __iomem *address = (void __iomem *)file->private_data;
- unsigned char *page;
- int retval;
int len = 0;
unsigned int value;
-
- if (*offset < 0)
- return -EINVAL;
- if (count == 0 || count > 1024)
- return 0;
- if (*offset != 0)
- return 0;
-
- page = (unsigned char *)__get_free_page(GFP_KERNEL);
- if (!page)
- return -ENOMEM;
+ char lbuf[20];

value = readl(address);
- len = sprintf(page, "%d\n", value);
-
- if (copy_to_user(buf, page, len)) {
- retval = -EFAULT;
- goto exit;
- }
- *offset += len;
- retval = len;
+ len = snprintf(lbuf, sizeof(lbuf), "%d\n", value);

-exit:
- free_page((unsigned long)page);
- return retval;
+ return simple_read_from_buffer(buf, count, offset, lbuf, len);
}

static ssize_t remote_settings_file_write(struct file *file, const char __user *ubuff, size_t count, loff_t *offset)