Re: [PATCH v2] ipr: fix out-of-bounds null overwrite

[Matthew R. Ochs]

On Jan 6, 2016, at 7:53 AM, Insu Yun  wrote:
> 
> Return value of snprintf is not bound by size value, 2nd argument.
> (https://www.kernel.org/doc/htmldocs/kernel-api/API-snprintf.html).
> Return value is number of printed chars, can be larger than 2nd argument.
> Therefore, it can write null byte out of bounds ofbuffer.
> Since snprintf puts null, it does not need to put additional null byte.
> 
> Signed-off-by: Insu Yun 
> ---
> drivers/scsi/ipr.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
> index 536cd5a..caf63f9 100644
> --- a/drivers/scsi/ipr.c
> +++ b/drivers/scsi/ipr.c
> @@ -4003,13 +4003,12 @@ static ssize_t ipr_store_update_fw(struct device *dev,
>   struct ipr_sglist *sglist;
>   char fname[100];
>   char *src;
> - int len, result, dnld_size;
> + int result, dnld_size;
> 
>   if (!capable(CAP_SYS_ADMIN))
>   return -EACCES;
> 
> - len = snprintf(fname, 99, "%s", buf);
> - fname[len-1] = '\0';
> + snprintf(fname, 99, "%s", buf);

Changing the 99 to sizeof(fname) as part of this change would also
make for cleaner code in my opinion. Will leave it up to you if you'd
like to do a v3.

Reviewed-by: Matthew R. Ochs  
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[PATCH v2] ipr: fix out-of-bounds null overwrite

[Insu Yun]

Return value of snprintf is not bound by size value, 2nd argument.
(https://www.kernel.org/doc/htmldocs/kernel-api/API-snprintf.html).
Return value is number of printed chars, can be larger than 2nd argument.
Therefore, it can write null byte out of bounds ofbuffer.
Since snprintf puts null, it does not need to put additional null byte.

Signed-off-by: Insu Yun 
---
 drivers/scsi/ipr.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
index 536cd5a..caf63f9 100644
--- a/drivers/scsi/ipr.c
+++ b/drivers/scsi/ipr.c
@@ -4003,13 +4003,12 @@ static ssize_t ipr_store_update_fw(struct device *dev,
struct ipr_sglist *sglist;
char fname[100];
char *src;
-   int len, result, dnld_size;
+   int result, dnld_size;
 
if (!capable(CAP_SYS_ADMIN))
return -EACCES;
 
-   len = snprintf(fname, 99, "%s", buf);
-   fname[len-1] = '\0';
+   snprintf(fname, 99, "%s", buf);
 
if (request_firmware(&fw_entry, fname, &ioa_cfg->pdev->dev)) {
dev_err(&ioa_cfg->pdev->dev, "Firmware file %s not found\n", 
fname);
-- 
1.9.1

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