linux-kernel - [PATCH next] fuse: Fix 'min: signedness error' in fuse_wr

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Message-Id: <20260113192243.73983-1-david.laight.linux@gmail.com>
Date: Tue, 13 Jan 2026 19:22:43 +0000
From: david.laight.linux@...il.com
To: Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Mark Brown <broonie@...nel.org>,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Kees Cook <kees@...nel.org>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Theodore Ts'o <tytso@....edu>,
	Brian Masney <bmasney@...hat.com>
Cc: David Laight <david.laight.linux@...il.com>
Subject: [PATCH next] fuse: Fix 'min: signedness error' in fuse_wr_pages()

From: David Laight <david.laight.linux@...il.com>

On 32bit systems 'pos' is s64 and everything else is 32bit so the
first argument to min() is signed - generating a warning.
On 64bit systems 'len' is 64bit unsigned forcing everything to unsigned.

Fix by reworking the exprssion to completely avoid 64bit maths on 32bit.
Use DIV_ROUND_UP() instead of open-coding something equivalent.

Note that the 32bit 'len' cannot overflow because the syscall interface
limits read/write (etc) to (INT_MAX - PAGE_SIZE) bytes (even on 64bit).

Fixes: 0f5bb0cfb0b4 ("fs: use min() or umin() instead of min_t()")
Signed-off-by: David Laight <david.laight.linux@...il.com>
---
 fs/fuse/file.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 2595b6b4922b..ff823b0545ed 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1323,8 +1323,8 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
 static inline unsigned int fuse_wr_pages(loff_t pos, size_t len,
 				     unsigned int max_pages)
 {
-	return min(((pos + len - 1) >> PAGE_SHIFT) - (pos >> PAGE_SHIFT) + 1,
-		   max_pages);
+	len += pos % PAGE_SIZE;
+	return min(DIV_ROUND_UP(len, PAGE_SIZE), max_pages);
 }
 
 static ssize_t fuse_perform_write(struct kiocb *iocb, struct iov_iter *ii)
-- 
2.39.5