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From: Jann Horn <jannh@google.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, jannh@google.com
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] x86/mtrr: don't copy out-of-bounds data in mtrr_write
Date: Fri,  6 Jul 2018 23:50:03 +0200
Message-ID: <20180706215003.156702-1-jannh@google.com> (raw)

Don't access the provided buffer out of bounds - this can cause a kernel
out-of-bounds read when invoked through sys_splice() or other things that
use kernel_write()/__kernel_write().

Fixes: 7f8ec5a4f01a ("x86/mtrr: Convert to use strncpy_from_user() helper")
Signed-off-by: Jann Horn <jannh@google.com>
---
 arch/x86/kernel/cpu/mtrr/if.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mtrr/if.c b/arch/x86/kernel/cpu/mtrr/if.c
index 4021d3859499..40eee6cc4124 100644
--- a/arch/x86/kernel/cpu/mtrr/if.c
+++ b/arch/x86/kernel/cpu/mtrr/if.c
@@ -106,7 +106,8 @@ mtrr_write(struct file *file, const char __user *buf, size_t len, loff_t * ppos)
 
 	memset(line, 0, LINE_SIZE);
 
-	length = strncpy_from_user(line, buf, LINE_SIZE - 1);
+	len = min_t(size_t, len, LINE_SIZE - 1);
+	length = strncpy_from_user(line, buf, len);
 	if (length < 0)
 		return length;
 
-- 
2.18.0.203.gfac676dfb9-goog


             reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-06 21:50 Jann Horn [this message]
2018-07-07 17:04 ` [tip:x86/urgent] x86/mtrr: Don't " tip-bot for Jann Horn
2018-07-09  6:52 ` [PATCH] x86/mtrr: don't " Andy Shevchenko
2018-07-09  7:41   ` Jann Horn
2018-07-09  8:20     ` Andy Shevchenko
2018-07-15 22:03     ` Ingo Molnar
2018-07-16  1:32       ` Jann Horn
2018-07-16  1:46         ` Linus Torvalds
2018-07-16  2:26       ` Al Viro

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