linux-kernel - [PATCH] mm/swapfile: fix an integer overflow in swap

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Message-Id: <20211006184011.2579054-1-aquini@redhat.com>
Date:   Wed,  6 Oct 2021 14:40:11 -0400
From:   Rafael Aquini <aquini@...hat.com>
To:     linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm/swapfile: fix an integer overflow in swap_show()

This one is just a minor nuisance for people going through /proc/swaps if
any of their swapareas is bigger than, or equal to 1073741824 pages (4TB).

seq_printf() format string casts as uint the conversion from pages to KB,
and that will overflow in the aforementioned case.

Albeit being almost unthinkable that someone would actually set up such big
of a single swaparea, there is a ticket recently filed against RHEL:
https://bugzilla.redhat.com/show_bug.cgi?id=2008812

Given that all other codesites that use format strings for the same swap
pages-to-KB conversion do cast it as ulong, this patch just follows suit.

Signed-off-by: Rafael Aquini <aquini@...hat.com>
---
 mm/swapfile.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 22d10f713848..29a7e3ebaaae 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2763,7 +2763,7 @@ static int swap_show(struct seq_file *swap, void *v)
 	struct swap_info_struct *si = v;
 	struct file *file;
 	int len;
-	unsigned int bytes, inuse;
+	unsigned long bytes, inuse;
 
 	if (si == SEQ_START_TOKEN) {
 		seq_puts(swap, "Filename\t\t\t\tType\t\tSize\t\tUsed\t\tPriority\n");
@@ -2775,7 +2775,7 @@ static int swap_show(struct seq_file *swap, void *v)
 
 	file = si->swap_file;
 	len = seq_file_path(swap, file, " \t\n\\");
-	seq_printf(swap, "%*s%s\t%u\t%s%u\t%s%d\n",
+	seq_printf(swap, "%*s%s\t%lu\t%s%lu\t%s%d\n",
 			len < 40 ? 40 - len : 1, " ",
 			S_ISBLK(file_inode(file)->i_mode) ?
 				"partition" : "file\t",
-- 
2.26.3