linux-kernel - [PATCH] fuse: fs-verity: aoid out-of-range comparison

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Message-Id: <20240730142802.1082627-1-arnd@kernel.org>
Date: Tue, 30 Jul 2024 16:27:52 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Miklos Szeredi <miklos@...redi.hu>,
	Richard Fung <richardfung@...gle.com>,
	Eric Biggers <ebiggers@...gle.com>
Cc: Arnd Bergmann <arnd@...db.de>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH] fuse: fs-verity: aoid out-of-range comparison

From: Arnd Bergmann <arnd@...db.de>

clang points out that comparing the 16-bit size of the digest against
SIZE_MAX is not a helpful comparison:

fs/fuse/ioctl.c:130:18: error: result of comparison of constant 18446744073709551611 with expression of type '__u16' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
        if (digest_size > SIZE_MAX - sizeof(struct fsverity_digest))
            ~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This either means tha tthe check can be removed entirely, or that the
intended comparison was for the 16-bit range. Assuming the latter was
intended, compare against U16_MAX instead.

Fixes: 9fe2a036a23c ("fuse: Add initial support for fs-verity")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/fuse/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fuse/ioctl.c b/fs/fuse/ioctl.c
index 572ce8a82ceb..5711d86c549d 100644
--- a/fs/fuse/ioctl.c
+++ b/fs/fuse/ioctl.c
@@ -127,7 +127,7 @@ static int fuse_setup_measure_verity(unsigned long arg, struct iovec *iov)
 	if (copy_from_user(&digest_size, &uarg->digest_size, sizeof(digest_size)))
 		return -EFAULT;
 
-	if (digest_size > SIZE_MAX - sizeof(struct fsverity_digest))
+	if (digest_size > U16_MAX - sizeof(struct fsverity_digest))
 		return -EINVAL;
 
 	iov->iov_len = sizeof(struct fsverity_digest) + digest_size;
-- 
2.39.2