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Sun, 27 Sep 2026 15:50:02 -0700 (PDT) Received: from spider.bream-herring.ts.net ([103.6.151.236]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a0ca127237sm5596551a91.4.2026.09.27.15.50.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 27 Sep 2026 15:50:01 -0700 (PDT) From: Matthias Goergens To: Andrew Morton Cc: Jan Kara , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] kdev_t: shift in dev_t in MKDEV() Date: Mon, 28 Sep 2026 06:49:58 +0800 Message-ID: <20260927224958.508964-1-matthias.goergens@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit MKDEV(ma, mi) evaluates ((ma) << MINORBITS) in whatever type the caller passes, usually int. For majors >= 2048 (legal: majors go up to 4095) the result exceeds INT_MAX, which C11 leaves undefined for a signed left shift; shifting a negative ma is undefined regardless of the major's value. In practice, on the compilers and two's complement targets the kernel supports, both cases wrap to the intended bit pattern; this patch makes the macro well defined regardless by casting the major to dev_t before shifting. For major and minor numbers in range, the device number it produces is unchanged. isofs feeds the Rock Ridge 'PN' entry's dev_high and dev_low into MKDEV() while holding them in int variables (fs/isofs/rock.c), so a crafted image can drive this exact shift. Fixing the macro covers every caller instead of just that one. Signed-off-by: Matthias Goergens --- include/linux/kdev_t.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/kdev_t.h b/include/linux/kdev_t.h index 4856706fbfeb..2dbbd47f1e68 100644 --- a/include/linux/kdev_t.h +++ b/include/linux/kdev_t.h @@ -9,7 +9,7 @@ #define MAJOR(dev) ((unsigned int) ((dev) >> MINORBITS)) #define MINOR(dev) ((unsigned int) ((dev) & MINORMASK)) -#define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi)) +#define MKDEV(ma, mi) (((dev_t)(ma) << MINORBITS) | (mi)) #define print_dev_t(buffer, dev) \ sprintf((buffer), "%u:%u\n", MAJOR(dev), MINOR(dev)) -- 2.55.0