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Tue, 31 Mar 2026 07:31:52 -0700 (PDT) Date: Tue, 31 Mar 2026 16:31:50 +0200 From: Petr Mladek To: Andy Shevchenko Cc: Josh Law , Steven Rostedt , Rasmus Villemoes , Sergey Senozhatsky , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/4] lib/vsprintf: use int for field_width in vsscanf() Message-ID: References: <20260324224940.50508-1-objecting@objecting.org> <20260324224940.50508-4-objecting@objecting.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed 2026-03-25 14:00:17, Andy Shevchenko wrote: > On Tue, Mar 24, 2026 at 10:49:39PM +0000, Josh Law wrote: > > vsscanf() declares field_width as s16 but assigns it from skip_atoi() > > which returns int. Values above 32767 silently truncate to negative, > > causing vsscanf() to abort all remaining parsing. This is inconsistent > > with struct printf_spec which uses int for field_width. > > Is the field_width an acceptable integer range by the specifications? I am not sure what is allowed by specification. Anyway, the code is not ready for a bigger values, for example: case 's': { char *s = (char *)va_arg(args, char *); if (field_width == -1) field_width = SHRT_MAX; clearly expects signed short int range. I wonder if it might even open some backdoor. The code matching as sequence of characters expects a defined field width, see case '[': { [...] /* field width is required */ if (field_width == -1) return num; The current code limits valid field width values to positive ones, aka SHRT_MAX which is clearly much lover than INT_MAX. And it might prevent some out of bound access. Best Regards, Petr