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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-486f421a617sm81548895e9.7.2026.03.18.08.12.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 08:12:52 -0700 (PDT) Date: Wed, 18 Mar 2026 15:12:50 +0000 From: David Laight To: Steven Rostedt Cc: "Masami Hiramatsu (Google)" , Ard Biesheuvel , Ilias Apalodimas , Josh Law , Andrew Morton , linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 1/1] lib/vsprintf: Limit the returning size to INT_MAX Message-ID: <20260318151250.40fef0ab@pumpkin> In-Reply-To: <20260318094733.1ada0513@gandalf.local.home> References: <177379678638.535490.18200744206158553364.stgit@devnote2> <177379679625.535490.15253547806594621828.stgit@devnote2> <20260318094733.1ada0513@gandalf.local.home> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 18 Mar 2026 09:47:33 -0400 Steven Rostedt wrote: > On Wed, 18 Mar 2026 10:19:56 +0900 > "Masami Hiramatsu (Google)" wrote: > > > From: Masami Hiramatsu (Google) > > > > There seems a design flaw of vsnprintf() whose return value can > > overflow the INT_MAX even on 32bit arch, because the buffer size is > > passed by 'size_t' but it returns the printed or required size in 'int'. > > > > The size_t is unsigned long, thus the caller can pass bigger than INT_MAX > > as the size of buffer (that is OK). But even the vsnprintf calculates > > the required/printed length correctly, if it overflows the INT_MAX, > > it can not return the size correctly by int. > > > > This should never happen but it should be checked and limited. > > > > Signed-off-by: Masami Hiramatsu (Google) > > --- > > drivers/firmware/efi/libstub/vsprintf.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/firmware/efi/libstub/vsprintf.c b/drivers/firmware/efi/libstub/vsprintf.c > > index 71c71c222346..1713cacecc25 100644 > > --- a/drivers/firmware/efi/libstub/vsprintf.c > > +++ b/drivers/firmware/efi/libstub/vsprintf.c > > @@ -549,7 +549,7 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list ap) > > if (size) > > buf[min(pos, size-1)] = '\0'; > > > > - return pos; > > + return (pos > INT_MAX) ? INT_MAX : pos; > > } > > > > int snprintf(char *buf, size_t size, const char *fmt, ...) > > Since this would require a buffer of size greater than 2G to be passed in, > I highly doubt this would happen anywhere in the kernel. > > If anything, it would be for "correctness" only, but I don't see this ever > being an issue within this century. What about the return value (on 32bit) from: snprintf(NULL, 0, " %*s %*s ", INT_MAX, "", INT_MAX, ""); This is more of a problem for libc. In reality there are easier ways to crash the kernel.... David > > -- Steve >