linux-kernel - [PATCH v2] drm: fix off-by-one in logger

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Date:   Wed, 23 May 2018 08:22:04 +0200
From:   Norbert Manthey <nmanthey@...zon.de>
To:     unlisted-recipients:; (no To-header on input)
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        <stable@...r.kernel.org>, Norbert Manthey <nmanthey@...zon.de>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        David Airlie <airlied@...ux.ie>,
        Harry Wentland <harry.wentland@....com>,
        Tony Cheng <tony.cheng@....com>,
        Yongqiang Sun <yongqiang.sun@....com>,
        Anthony Koo <Anthony.Koo@....com>,
        Michel Dänzer <michel.daenzer@....com>,
        Dmytro Laktyushkin <Dmytro.Laktyushkin@....com>,
        Jordan Lazare <Jordan.Lazare@....com>,
        "Colin Ian King" <colin.king@...onical.com>,
        <amd-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] drm: fix off-by-one in logger

The current implementation will leak a byte to the log via memmove. The
specified 27 bytes are off-by-one, as the payload is 25 bytes, and the
termination character is only one byte large. To avoid this, factor out
the error message, and furthermore make the second parameter of the
append_entry function const.

The full trace is as follows:

In function ‘memmove’,
   from ‘append_entry’ at
        drivers/gpu/drm/amd/display/dc/basics/logger.c:257:2,
   from ‘dm_logger_append_va’ at
        drivers/gpu/drm/amd/display/dc/basics/logger.c:348:4
   detected read beyond size of object passed as 2nd parameter

Signed-off-by: Norbert Manthey <nmanthey@...zon.de>
---
 drivers/gpu/drm/amd/display/dc/basics/logger.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/basics/logger.c b/drivers/gpu/drm/amd/display/dc/basics/logger.c
index 31bee05..6ba8d0c 100644
--- a/drivers/gpu/drm/amd/display/dc/basics/logger.c
+++ b/drivers/gpu/drm/amd/display/dc/basics/logger.c
@@ -244,7 +244,7 @@ static void log_heading(struct log_entry *entry)
 
 static void append_entry(
 		struct log_entry *entry,
-		char *buffer,
+		const char *buffer,
 		uint32_t buf_size)
 {
 	if (!entry->buf ||
@@ -346,7 +346,9 @@ void dm_logger_append_va(
 		if (size < LOG_MAX_LINE_SIZE - 1) {
 			append_entry(entry, buffer, size);
 		} else {
-			append_entry(entry, "LOG_ERROR, line too long\n", 27);
+			static const char msg[] = "LOG_ERROR, line too long\n";
+
+			append_entry(entry, msg, sizeof(msg));
 		}
 	}
 }
-- 
2.7.4

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