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Fri, 20 Mar 2026 09:51:50 -0700 (PDT) Date: Fri, 20 Mar 2026 17:51:48 +0100 From: Petr Mladek To: "Masami Hiramatsu (Google)" Cc: Steven Rostedt , Andy Shevchenko , Rasmus Villemoes , Sergey Senozhatsky , Andrew Morton , David Laight , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/2] lib/vsprintf: Limit the returning size to INT_MAX Message-ID: References: <177397887883.33018.9867883986177366222.stgit@devnote2> <177397889735.33018.16696041032174901196.stgit@devnote2> 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: <177397889735.33018.16696041032174901196.stgit@devnote2> On Fri 2026-03-20 12:54:57, Masami Hiramatsu (Google) wrote: > From: Masami Hiramatsu (Google) > > The return value of vsnprintf() can overflow INT_MAX and return > a minus value. In the @size is checked input overflow, but it does > not check the output, which is expected required size. > > This should never happen but it should be checked and limited. Great catch! > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -2985,7 +2985,7 @@ int vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args) > } > > /* the trailing null byte doesn't count towards the total */ > - return str-buf; > + return WARN_ON_ONCE(str - buf > INT_MAX) ? INT_MAX : str - buf; Is it guaranteed that the pointer arithmetic will be a big enough unsigned number type? I would rather do a cast to be on the safe side, for example: return WARN_ON_ONCE((size_t)(str - buf) > INT_MAX) ? INT_MAX : str - buf; or even use a variable to make it better readable: size_t ret_size; ret_size = str - buf; if (WARN_ON_ONCE(ret_size > INT_MAX)) ret_size = INT_MAX; return ret_size; Best Regards, Petr