linux-kernel - Re: [PATCH 4/4] file: Fix file descriptor leak in copy_fd

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Message-ID: <YkP2hKKeMeFrdpBW@zx2c4.com>
Date:   Wed, 30 Mar 2022 02:21:14 -0400
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Fedor Pchelkin <aissur0002@...il.com>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Eric Biggers <ebiggers@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] file: Fix file descriptor leak in copy_fd_bitmaps()

Hi Linus,

On Tue, Mar 29, 2022 at 11:08:55PM -0700, Linus Torvalds wrote:
> So does it help if you just remove that
> 
>         max_fds = ALIGN(max_fds, BITS_PER_LONG);
> 
> and instead make the final return be
> 
>         return ALIGN(min(count, max_fds), BITS_PER_LONG);
> 
> instead?

Yep, that works:

diff --git a/fs/file.c b/fs/file.c
index c01c29417ae6..ee9317346702 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -303,10 +303,9 @@ static unsigned int sane_fdtable_size(struct fdtable *fdt, unsigned int max_fds)
 	unsigned int count;

 	count = count_open_files(fdt);
-	max_fds = ALIGN(max_fds, BITS_PER_LONG);
 	if (max_fds < NR_OPEN_DEFAULT)
 		max_fds = NR_OPEN_DEFAULT;
-	return min(count, max_fds);
+	return ALIGN(min(count, max_fds), BITS_PER_LONG);
 }

 /*

Jason