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Subject[PATCH 4/8] staging: comedi: avoid bad truncation of a size_t in comedi_write()
Date
At one point in `comedi_write()`, the variable `n` gets assigned to the
minimum of the parameter `nbytes` and the amount of writeable buffer
space. The way that is done currently is unsafe in the unlikely case
that `nbytes` exceeds `UINT_MAX`, so fix it.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
---
drivers/staging/comedi/comedi_fops.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 188a12a..8c784c4 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2357,16 +2357,13 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
break;
}

- n = nbytes;
-
- m = n;
+ /* Allocate all free buffer space. */
+ comedi_buf_write_alloc(s, async->prealloc_bufsz);
+ m = comedi_buf_write_n_allocated(s);
+ /* Avoid buffer wraparound. */
if (async->buf_write_ptr + m > async->prealloc_bufsz)
m = async->prealloc_bufsz - async->buf_write_ptr;
- comedi_buf_write_alloc(s, async->prealloc_bufsz);
- if (m > comedi_buf_write_n_allocated(s))
- m = comedi_buf_write_n_allocated(s);
- if (m < n)
- n = m;
+ n = min_t(size_t, m, nbytes);

if (n == 0) {
if (file->f_flags & O_NONBLOCK) {
--
2.6.2


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