linux-kernel - [PATCH] mm: Make kvmalloc refuse to allocate more than 2GB

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Message-Id: <20210721184131.2264356-1-willy@infradead.org>
Date:   Wed, 21 Jul 2021 19:41:31 +0100
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     Al Viro <viro@...iv.linux.org.uk>,
        Qualys Security Advisory <qsa@...lys.com>,
        Eric Sandeen <sandeen@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: [PATCH] mm: Make kvmalloc refuse to allocate more than 2GB

It's generally dangerous to allocate such large quantities of memory
within the kernel owing to our propensity to use 'int' to represent
a length.  If somebody really needs it, we can add a kvmalloc_large()
later, but let's default to "You can't allocate that much memory".

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 fs/seq_file.c                                     | 3 ---
 mm/util.c                                         | 7 +++++++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 4a2cda04d3e2..b117b212ef28 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -32,9 +32,6 @@ static void seq_set_overflow(struct seq_file *m)
 
 static void *seq_buf_alloc(unsigned long size)
 {
-	if (unlikely(size > MAX_RW_COUNT))
-		return NULL;
-
 	return kvmalloc(size, GFP_KERNEL_ACCOUNT);
 }
 
diff --git a/mm/util.c b/mm/util.c
index 9043d03750a7..8ff2a8924d5f 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -593,6 +593,13 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
 	if (ret || size <= PAGE_SIZE)
 		return ret;
 
+	/*
+	 * Succeeding for sizes above 2GiB can lead to truncation if
+	 * someone casts the size to an int.
+	 */
+	if (size > INT_MAX)
+		return NULL;
+
 	return __vmalloc_node(size, 1, flags, node,
 			__builtin_return_address(0));
 }
-- 
2.30.2