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From:   Mathieu Malaterre <malat@debian.org>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Mathieu Malaterre <malat@debian.org>,
        Nick Desaulniers <nick.desaulniers@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org
Subject: [PATCH] writeback: tracing: Copy only up to 31 characters in strncpy() calls
Date:   Fri, 18 Jan 2019 20:32:00 +0100
Message-Id: <20190118193200.32691-1-malat@debian.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

In the past an attempt was made to remove a set of warnings triggered by
gcc 8.x and W=1 by changing calls to strncpy() into strlcpy(). This was
rejected as one of the desired behavior is to keep initializing the rest
of the destination string whenever the source string is less than the
size.

However the code makes it clear that this is not a desired behavior to
copy the entire 32 characters into the destination buffer, since it is
expected that the string is NUL terminated. So change the maximum number
of characters to be copied to be the size of the destination buffer
minus 1.

Break long lines and make this patch go through `checkpatch --strict` with
no errors.

This commit removes the following warnings:

  include/trace/events/writeback.h:69:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  include/trace/events/writeback.h:99:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  include/trace/events/writeback.h:179:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  include/trace/events/writeback.h:223:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  include/trace/events/writeback.h:277:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  include/trace/events/writeback.h:299:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  include/trace/events/writeback.h:324:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  include/trace/events/writeback.h:375:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  include/trace/events/writeback.h:586:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]
  include/trace/events/writeback.h:660:3: warning: 'strncpy' specified bound 32 equals destination size [-Wstringop-truncation]

Cc: Nick Desaulniers <nick.desaulniers@gmail.com>
Link: https://lore.kernel.org/patchwork/patch/910830/
Signed-off-by: Mathieu Malaterre <malat@debian.org>
---
 include/trace/events/writeback.h | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 32db72c7c055..7bc58980f84f 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -67,7 +67,8 @@ TRACE_EVENT(writeback_dirty_page,
 
 	TP_fast_assign(
 		strncpy(__entry->name,
-			mapping ? dev_name(inode_to_bdi(mapping->host)->dev) : "(unknown)", 32);
+			mapping ? dev_name(inode_to_bdi(mapping->host)->dev) :
+			"(unknown)", sizeof(__entry->name) - 1);
 		__entry->ino = mapping ? mapping->host->i_ino : 0;
 		__entry->index = page->index;
 	),
@@ -97,7 +98,8 @@ DECLARE_EVENT_CLASS(writeback_dirty_inode_template,
 
 		/* may be called for files on pseudo FSes w/ unregistered bdi */
 		strncpy(__entry->name,
-			bdi->dev ? dev_name(bdi->dev) : "(unknown)", 32);
+			bdi->dev ? dev_name(bdi->dev) : "(unknown)",
+			sizeof(__entry->name) - 1);
 		__entry->ino		= inode->i_ino;
 		__entry->state		= inode->i_state;
 		__entry->flags		= flags;
@@ -177,7 +179,8 @@ DECLARE_EVENT_CLASS(writeback_write_inode_template,
 
 	TP_fast_assign(
 		strncpy(__entry->name,
-			dev_name(inode_to_bdi(inode)->dev), 32);
+			dev_name(inode_to_bdi(inode)->dev),
+			sizeof(__entry->name) - 1);
 		__entry->ino		= inode->i_ino;
 		__entry->sync_mode	= wbc->sync_mode;
 		__entry->cgroup_ino	= __trace_wbc_assign_cgroup(wbc);
@@ -221,7 +224,8 @@ DECLARE_EVENT_CLASS(writeback_work_class,
 	),
 	TP_fast_assign(
 		strncpy(__entry->name,
-			wb->bdi->dev ? dev_name(wb->bdi->dev) : "(unknown)", 32);
+			wb->bdi->dev ? dev_name(wb->bdi->dev) : "(unknown)",
+			sizeof(__entry->name) - 1);
 		__entry->nr_pages = work->nr_pages;
 		__entry->sb_dev = work->sb ? work->sb->s_dev : 0;
 		__entry->sync_mode = work->sync_mode;
@@ -274,7 +278,8 @@ DECLARE_EVENT_CLASS(writeback_class,
 		__field(unsigned int, cgroup_ino)
 	),
 	TP_fast_assign(
-		strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
+		strncpy(__entry->name, dev_name(wb->bdi->dev),
+			sizeof(__entry->name) - 1);
 		__entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
 	),
 	TP_printk("bdi %s: cgroup_ino=%u",
@@ -296,7 +301,8 @@ TRACE_EVENT(writeback_bdi_register,
 		__array(char, name, 32)
 	),
 	TP_fast_assign(
-		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		strncpy(__entry->name, dev_name(bdi->dev),
+			sizeof(__entry->name) - 1);
 	),
 	TP_printk("bdi %s",
 		__entry->name
@@ -321,7 +327,8 @@ DECLARE_EVENT_CLASS(wbc_class,
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		strncpy(__entry->name, dev_name(bdi->dev),
+			sizeof(__entry->name) - 1);
 		__entry->nr_to_write	= wbc->nr_to_write;
 		__entry->pages_skipped	= wbc->pages_skipped;
 		__entry->sync_mode	= wbc->sync_mode;
@@ -372,7 +379,8 @@ TRACE_EVENT(writeback_queue_io,
 	),
 	TP_fast_assign(
 		unsigned long *older_than_this = work->older_than_this;
-		strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
+		strncpy(__entry->name, dev_name(wb->bdi->dev),
+			sizeof(__entry->name) - 1);
 		__entry->older	= older_than_this ?  *older_than_this : 0;
 		__entry->age	= older_than_this ?
 				  (jiffies - *older_than_this) * 1000 / HZ : -1;
@@ -584,7 +592,8 @@ TRACE_EVENT(writeback_sb_inodes_requeue,
 
 	TP_fast_assign(
 		strncpy(__entry->name,
-		        dev_name(inode_to_bdi(inode)->dev), 32);
+			dev_name(inode_to_bdi(inode)->dev),
+			sizeof(__entry->name) - 1);
 		__entry->ino		= inode->i_ino;
 		__entry->state		= inode->i_state;
 		__entry->dirtied_when	= inode->dirtied_when;
@@ -658,7 +667,8 @@ DECLARE_EVENT_CLASS(writeback_single_inode_template,
 
 	TP_fast_assign(
 		strncpy(__entry->name,
-			dev_name(inode_to_bdi(inode)->dev), 32);
+			dev_name(inode_to_bdi(inode)->dev),
+			sizeof(__entry->name) - 1);
 		__entry->ino		= inode->i_ino;
 		__entry->state		= inode->i_state;
 		__entry->dirtied_when	= inode->dirtied_when;
-- 
2.19.2