On Sat, 7 Jul 2018 05:37:22 +0200
Jann Horn <ja...@google.com> wrote:
> The first checks in mtdchar_read() and mtdchar_write() attempt to limit
> `count` such that `*ppos + count <= mtd->size`. However, they ignore the
> possibility of `*ppos > mtd->size`, allowing the calculation of `count` to
> wrap around. `mtdchar_lseek()` prevents seeking beyond mtd->size, but the
> pread/pwrite syscalls bypass this.
>
> I haven't found any codepath on which this actually causes dangerous
> behavior, but it seems like a sensible change anyway.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Jann Horn <ja...@google.com>
Applied.
Thanks,
Boris
> ---
> drivers/mtd/mtdchar.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
> index cd67c85cc87d..02389528f622 100644
> --- a/drivers/mtd/mtdchar.c
> +++ b/drivers/mtd/mtdchar.c
> @@ -160,8 +160,12 @@ static ssize_t mtdchar_read(struct file *file, char
> __user *buf, size_t count,
>
> pr_debug("MTD_read\n");
>
> - if (*ppos + count > mtd->size)
> - count = mtd->size - *ppos;
> + if (*ppos + count > mtd->size) {
> + if (*ppos < mtd->size)
> + count = mtd->size - *ppos;
> + else
> + count = 0;
> + }
>
> if (!count)
> return 0;
> @@ -246,7 +250,7 @@ static ssize_t mtdchar_write(struct file *file, const
> char __user *buf, size_t c
>
> pr_debug("MTD_write\n");
>
> - if (*ppos == mtd->size)
> + if (*ppos >= mtd->size)
> return -ENOSPC;
>
> if (*ppos + count > mtd->size)
