linux-kernel - [PATCH] [next] ARM: Replace snprintf() with the safer scnprintf() variant

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Message-ID: <Zv9aEoDo1k36Hg3H@mail.google.com>
Date: Fri, 4 Oct 2024 15:59:30 +1300
From: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>
To: linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org
Cc: paulo.miguel.almeida.rodenas@...il.com, linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] [next] ARM: Replace snprintf() with the safer scnprintf()
 variant

There is a general misunderstanding amongst engineers that {v}snprintf()
returns the length of the data *actually* encoded into the destination
array.  However, as per the C99 standard {v}snprintf() really returns
the length of the data that *would have been* written if there were
enough space for it.  This misunderstanding has led to buffer-overruns
in the past.  It's generally considered safer to use the {v}scnprintf()
variants in their place (or even sprintf() in simple cases).

Link: https://lwn.net/Articles/69419/
Link: https://github.com/KSPP/linux/issues/105
Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>
---
 arch/arm/kernel/process.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index e16ed102960c..9d768a93fb1c 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -186,8 +186,8 @@ void __show_regs(struct pt_regs *regs)
 			unsigned int transbase;
 			asm("mrc p15, 0, %0, c2, c0\n\t"
 			    : "=r" (transbase));
-			snprintf(buf, sizeof(buf), "  Table: %08x  DAC: %08x",
-				transbase, domain);
+			scnprintf(buf, sizeof(buf), "  Table: %08x  DAC: %08x",
+				  transbase, domain);
 		}
 #endif
 		asm("mrc p15, 0, %0, c1, c0\n" : "=r" (ctrl));
-- 
2.46.0