[Cocci] [PATCH] coccinelle: semantic patch to check for inappropriate do_div() calls

[Wen Yang <wenyang@linux.alibaba.com>]

do_div() does a 64-by-32 division.
When the divisor is unsigned long, u64, or s64,
do_div() truncates it to 32 bits, this means it
can test non-zero and be truncated to zero for division.
This semantic patch is inspired by Mateusz Guzik's patch:
commit b0ab99e7736a ("sched: Fix possible divide by zero in avg_atom() calculation")

Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Cc: Julia Lawall <Julia.Lawall@lip6.fr>
Cc: Gilles Muller <Gilles.Muller@lip6.fr>
Cc: Nicolas Palix <nicolas.palix@imag.fr>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Matthias Maennich <maennich@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: cocci@systeme.lip6.fr
Cc: linux-kernel@vger.kernel.org
---
 scripts/coccinelle/misc/do_div.cocci | 66 ++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 scripts/coccinelle/misc/do_div.cocci

diff --git a/scripts/coccinelle/misc/do_div.cocci b/scripts/coccinelle/misc/do_div.cocci
new file mode 100644
index 0000000..f1b72d1
--- /dev/null
+++ b/scripts/coccinelle/misc/do_div.cocci
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/// do_div() does a 64-by-32 division.
+/// When the divisor is unsigned long, u64, or s64,
+/// do_div() truncates it to 32 bits, this means it
+/// can test non-zero and be truncated to zero for division.
+///
+//# This makes an effort to find those inappropriate do_div () calls.
+//
+// Confidence: Moderate
+// Copyright: (C) 2020 Wen Yang, Alibaba.
+// Comments:
+// Options: --no-includes --include-headers
+
+virtual context
+virtual org
+virtual report
+
+@depends on context@
+expression f;
+long l;
+unsigned long ul;
+u64 ul64;
+s64 sl64;
+
+@@
+(
+* do_div(f, l);
+|
+* do_div(f, ul);
+|
+* do_div(f, ul64);
+|
+* do_div(f, sl64);
+)
+
+@r depends on (org || report)@
+expression f;
+long l;
+unsigned long ul;
+position p;
+u64 ul64;
+s64 sl64;
+@@
+(
+do_div@p(f, l);
+|
+do_div@p(f, ul);
+|
+do_div@p(f, ul64);
+|
+do_div@p(f, sl64);
+)
+
+@script:python depends on org@
+p << r.p;
+@@
+
+msg="WARNING: WARNING: do_div() does a 64-by-32 division, which may truncation the divisor to 32-bit"
+coccilib.org.print_todo(p[0], msg)
+
+@script:python depends on report@
+p << r.p;
+@@
+
+msg="WARNING: WARNING: do_div() does a 64-by-32 division, which may truncation the divisor to 32-bit"
+coccilib.report.print_report(p[0], msg)
-- 
1.8.3.1

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