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SubjectRe: [PATCH] tty: nozomi: avoid sprintf buffer overflow
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On 11/28/2016, 10:04 PM, Arnd Bergmann wrote:
> Testing with a gcc-7 snapshot produced an internal compiler error
> for this file:
>
> drivers/tty/nozomi.c: In function 'receive_flow_control':
> drivers/tty/nozomi.c:919:12: internal compiler error: in get_substring_ranges_for_loc, at input.c:1388
> static int receive_flow_control(struct nozomi *dc)
>
> I've reported this at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78569
> but also noticed that the code line contains a stack overflow, as it prints
> a string into a slightly shorter fixed-length 'tmp' variable.
>
> I don't see any point in the temporary variable, we can simply use
> pr_debug() to print the output directly. This change should not change
> any of the output but avoids both the stack overflow and the gcc
> crash.
>
> The stack overflow will not happen unless a module load parameter is
> also set to enable the debug messages.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> drivers/tty/nozomi.c | 9 ++-------
> 1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/tty/nozomi.c b/drivers/tty/nozomi.c
> index e2020a691058..17a182b28d52 100644
> --- a/drivers/tty/nozomi.c
> +++ b/drivers/tty/nozomi.c
> @@ -69,13 +69,8 @@
> #define NOZOMI_DEBUG_LEVEL 0x00
>
> #define P_BUF_SIZE 128
> -#define NFO(_err_flag_, args...) \
> -do { \
> - char tmp[P_BUF_SIZE]; \
> - snprintf(tmp, sizeof(tmp), ##args); \
> - printk(_err_flag_ "[%d] %s(): %s\n", __LINE__, \
> - __func__, tmp); \
> -} while (0)
> +#define NFO(_err_flag_, fmt, args...) \
> + pr_debug("[%d] %s(): " fmt "\n", __LINE__, __func__, ##args);

Could you also kill the now unused _err_flag_ parameter (including the
only user of NFO)?

(Or inline pr_debug directly into the only user and kill NFO completely?)

thanks,
--
js
suse labs

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