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    SubjectRe: [PATCH] SUNRPC: Prevent kernel stack corruption on long values of flush
    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.

    But I'm obviously confused, because I don't understand why tbuf needs to be
    any more than 10 + 2.


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