linux-kernel - [PATCH] fs/file: fix the check in find_next

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Date: Thu, 30 May 2024 00:06:56 +0800
From: Yuntao Wang <yuntao.wang@...ux.dev>
To: linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	Yuntao Wang <yuntao.wang@...ux.dev>
Subject: [PATCH] fs/file: fix the check in find_next_fd()

The maximum possible return value of find_next_zero_bit(fdt->full_fds_bits,
maxbit, bitbit) is maxbit. This return value, multiplied by BITS_PER_LONG,
gives the value of bitbit, which can never be greater than maxfd, it can
only be equal to maxfd at most, so the following check 'if (bitbit > maxfd)'
will never be true.

Moreover, when bitbit equals maxfd, it indicates that there are no unused
fds, and the function can directly return.

Fix this check.

Signed-off-by: Yuntao Wang <yuntao.wang@...ux.dev>
---
 fs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/file.c b/fs/file.c
index 8076aef9c210..7058901a2154 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -491,7 +491,7 @@ static unsigned int find_next_fd(struct fdtable *fdt, unsigned int start)
 	unsigned int bitbit = start / BITS_PER_LONG;

 	bitbit = find_next_zero_bit(fdt->full_fds_bits, maxbit, bitbit) * BITS_PER_LONG;
-	if (bitbit > maxfd)
+	if (bitbit >= maxfd)
 		return maxfd;
 	if (bitbit > start)
 		start = bitbit;
-- 
2.45.1