linux-kernel - [PATCH] Adjust sysrq_register_handler() to avoid an array subscript warning

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Message-ID: <20150428094939.23440.50962.stgit@warthog.procyon.org.uk>
Date:	Tue, 28 Apr 2015 10:49:39 +0100
From:	David Howells <dhowells@...hat.com>
To:	torvalds@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, mathieu.poirier@...aro.org
Subject: [PATCH] Adjust sysrq_register_handler() to avoid an array subscript
 warning

sysrq_register_handler() iterates over platform_sysrq_reset_seq[] using
ARRAY_SIZE() on sysrq_reset_seq[] as a limit (indeed, the platform array is
expected to be shorter).  gcc-5 spots the potential dereference beyond the end
of the array and issues the following warnings:

  CC      drivers/tty/sysrq.o
../drivers/tty/sysrq.c: In function 'sysrq_init':
../drivers/tty/sysrq.c:958:33: warning: array subscript is above array bounds [-Warray-bounds]
   key = platform_sysrq_reset_seq[i];
                                 ^
../drivers/tty/sysrq.c: In function 'sysrq_toggle_support':
../drivers/tty/sysrq.c:958:33: warning: array subscript is above array bounds [-Warray-bounds]
   key = platform_sysrq_reset_seq[i];
                                 ^

Since the platform_sysrq_reset_seq[] array is apparently meant to be
terminated rather than being fixed length, use a pointer to iterate over it
instead.

One further note: Should platform_sysrq_reset_seq[] be const?

Signed-off-by: David Howells <dhowells@...hat.com>
---

 drivers/tty/sysrq.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 843f2cdc280b..431af8b6bdb7 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -949,13 +949,14 @@ static bool sysrq_handler_registered;
 
 static inline void sysrq_register_handler(void)
 {
+	const unsigned short *p = platform_sysrq_reset_seq;
 	unsigned short key;
 	int error;
 	int i;
 
 	/* First check if a __weak interface was instantiated. */
 	for (i = 0; i < ARRAY_SIZE(sysrq_reset_seq); i++) {
-		key = platform_sysrq_reset_seq[i];
+		key = *p++;
 		if (key == KEY_RESERVED || key > KEY_MAX)
 			break;
 

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