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Subject[PATCH] sgi-gru: Fix kernel stack buffer overrun
Date
This patch fixes a kernel stack buffer overrun in the sgi-gru procfs
interface implementation.
The "count" parameter to options_write() is user controlled. So this bug
can be used to write '\0' bytes to almost arbitrary places on the kernel stack.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Cc: stable@kernel.org

---
This procfs file has 0644 permissions, so the bug is probably not exploitable
for local privilege escalation.

---
drivers/misc/sgi-gru/gruprocfs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- linux-2.6.orig/drivers/misc/sgi-gru/gruprocfs.c
+++ linux-2.6/drivers/misc/sgi-gru/gruprocfs.c
@@ -157,23 +157,23 @@ static int options_show(struct seq_file
seq_printf(s, "0x%lx\n", gru_options);
return 0;
}

static ssize_t options_write(struct file *file, const char __user *userbuf,
size_t count, loff_t *data)
{
unsigned long val;
char buf[80];

+ memset(buf, 0, sizeof(buf));
if (strncpy_from_user(buf, userbuf, sizeof(buf) - 1) < 0)
return -EFAULT;
- buf[count - 1] = '\0';
if (!strict_strtoul(buf, 10, &val))
gru_options = val;

return count;
}

static int cch_seq_show(struct seq_file *file, void *data)
{
long gid = *(long *)data;
int i;
--
Greetings, Michael.


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