linux-kernel - [PATCH 3.2 082/126] swapfile: fix memory corruption via malformed swapfile

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Message-ID: <lsq.1487198494.926801282@decadent.org.uk>
Date:   Wed, 15 Feb 2017 22:41:34 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jerome Marchand" <jmarchan@...hat.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Hugh Dickins" <hughd@...gle.com>,
        "Johannes Weiner" <hannes@...xchg.org>,
        "Kees Cook" <keescook@...omium.org>,
        "Vlastimil Babka" <vbabka@...e.cz>, "Jann Horn" <jann@...jh.net>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH 3.2 082/126] swapfile: fix memory corruption via malformed
 swapfile

3.2.85-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jann Horn <jann@...jh.net>

commit dd111be69114cc867f8e826284559bfbc1c40e37 upstream.

When root activates a swap partition whose header has the wrong
endianness, nr_badpages elements of badpages are swabbed before
nr_badpages has been checked, leading to a buffer overrun of up to 8GB.

This normally is not a security issue because it can only be exploited
by root (more specifically, a process with CAP_SYS_ADMIN or the ability
to modify a swap file/partition), and such a process can already e.g.
modify swapped-out memory of any other userspace process on the system.

Link: http://lkml.kernel.org/r/1477949533-2509-1-git-send-email-jann@thejh.net
Signed-off-by: Jann Horn <jann@...jh.net>
Acked-by: Kees Cook <keescook@...omium.org>
Acked-by: Jerome Marchand <jmarchan@...hat.com>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/swapfile.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1913,6 +1913,8 @@ static unsigned long read_swap_header(st
 		swab32s(&swap_header->info.version);
 		swab32s(&swap_header->info.last_page);
 		swab32s(&swap_header->info.nr_badpages);
+		if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
+			return 0;
 		for (i = 0; i < swap_header->info.nr_badpages; i++)
 			swab32s(&swap_header->info.badpages[i]);
 	}