On Wed, Jul 18, 2012 at 04:00:49PM -0400, Jim Rees wrote:
> J. Bruce Fields wrote:
>
> On Tue, Jul 17, 2012 at 12:01:26AM +0200, Sasha Levin wrote:
> > The buffer size in read_flush() is too small for the longest possible values
> > for it. This can lead to a kernel stack corruption:
>
> Thanks!
>
> >
> > diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> > index 2afd2a8..f86d95e 100644
> > --- a/net/sunrpc/cache.c
> > +++ b/net/sunrpc/cache.c
> > @@ -1409,11 +1409,11 @@ static ssize_t read_flush(struct file *file, char __user *buf,
> > size_t count, loff_t *ppos,
> > struct cache_detail *cd)
> > {
> > - char tbuf[20];
> > + char tbuf[22];
>
> I wonder how common this sort of calculation is in the kernel? It might
> provide some peace of mind to be able to write this something like
>
> char tbuf[MAXLEN_BASE10_UL + 2] /* + 2 for final "\n\0" */
>
> You could use something like:
>
> char tbuf[sizeof (unsigned long) * 24 / 10 + 1 + 2]; /* + 2 for final "\n\0" */
>
> since there are roughly 10 bits for every 3 decimal digits.
So we could do something like this. OK, I'm not sure I care enough.
--b.
diff --git a/include/linux/string.h b/include/linux/string.h
index e033564..ed34180 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -126,6 +126,10 @@ extern void argv_free(char **argv);
extern bool sysfs_streq(const char *s1, const char *s2);
extern int strtobool(const char *s, bool *res);
+/* length of the decimal representation of an unsigned integer. Just an
+ * approximation, but it's right for types of size 1 to 36 bytes: */
+#define base10len(i) (sizeof(i) * 24 / 10 + 1)
+
#ifdef CONFIG_BINARY_PRINTF
int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args);
int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf);
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 2afd2a8..1dcd2b3 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1409,7 +1409,7 @@ static ssize_t read_flush(struct file *file, char __user *buf,
size_t count, loff_t *ppos,
struct cache_detail *cd)
{
- char tbuf[20];
+ char tbuf[base10len(unsigned long) + 2];
unsigned long p = *ppos;
size_t len;
--
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