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* [PATCH v3] writeback: fix -Wstringop-truncation warnings
@ 2019-07-25 17:18 Qian Cai
  2019-07-30 17:22 ` Jan Kara
  0 siblings, 1 reply; 2+ messages in thread
From: Qian Cai @ 2019-07-25 17:18 UTC (permalink / raw)
  To: akpm
  Cc: tobin, rostedt, mingo, tj, dchinner, fengguang.wu, jack, axboe,
	linux-kernel, Qian Cai

There are many of those warnings.

In file included from ./arch/powerpc/include/asm/paca.h:15,
                 from ./arch/powerpc/include/asm/current.h:13,
                 from ./include/linux/thread_info.h:21,
                 from ./include/asm-generic/preempt.h:5,
                 from ./arch/powerpc/include/generated/asm/preempt.h:1,
                 from ./include/linux/preempt.h:78,
                 from ./include/linux/spinlock.h:51,
                 from fs/fs-writeback.c:19:
In function 'strncpy',
    inlined from 'perf_trace_writeback_page_template' at
./include/trace/events/writeback.h:56:1:
./include/linux/string.h:260:9: warning: '__builtin_strncpy' specified
bound 32 equals destination size [-Wstringop-truncation]
  return __builtin_strncpy(p, q, size);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix it by using the new strscpy_pad() which was introduced in the
commit 458a3bf82df4 ("lib/string: Add strscpy_pad() function") and will
always be NUL-terminated instead of strncpy(). Also, changes strlcpy()
to use strscpy_pad() in this file for consistency.

Fixes: 455b2864686d ("writeback: Initial tracing support")
Fixes: 028c2dd184c0 ("writeback: Add tracing to balance_dirty_pages")
Fixes: e84d0a4f8e39 ("writeback: trace event writeback_queue_io")
Fixes: b48c104d2211 ("writeback: trace event bdi_dirty_ratelimit")
Fixes: cc1676d917f3 ("writeback: Move requeueing when I_SYNC set to writeback_sb_inodes()")
Fixes: 9fb0a7da0c52 ("writeback: add more tracepoints")
Signed-off-by: Qian Cai <cai@lca.pw>
---

v3: Rearrange a long-line a bit to make the code more readable.
v2: Use strscpy_pad() to address the possible data leaking concern from Steve [1].
    Replace strlcpy() as well for consistency.

[1] https://lore.kernel.org/lkml/20190716170339.1c44719d@gandalf.local.home/

 include/trace/events/writeback.h | 38 ++++++++++++++++++++------------------
 1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index aa7f3aeac740..79095434c1be 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -66,8 +66,9 @@
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name,
-			mapping ? dev_name(inode_to_bdi(mapping->host)->dev) : "(unknown)", 32);
+		strscpy_pad(__entry->name,
+			    mapping ? dev_name(inode_to_bdi(mapping->host)->dev) : "(unknown)",
+			    32);
 		__entry->ino = mapping ? mapping->host->i_ino : 0;
 		__entry->index = page->index;
 	),
@@ -110,8 +111,8 @@
 		struct backing_dev_info *bdi = inode_to_bdi(inode);
 
 		/* may be called for files on pseudo FSes w/ unregistered bdi */
-		strncpy(__entry->name,
-			bdi->dev ? dev_name(bdi->dev) : "(unknown)", 32);
+		strscpy_pad(__entry->name,
+			    bdi->dev ? dev_name(bdi->dev) : "(unknown)", 32);
 		__entry->ino		= inode->i_ino;
 		__entry->state		= inode->i_state;
 		__entry->flags		= flags;
@@ -190,8 +191,8 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name,
-			dev_name(inode_to_bdi(inode)->dev), 32);
+		strscpy_pad(__entry->name,
+			    dev_name(inode_to_bdi(inode)->dev), 32);
 		__entry->ino		= inode->i_ino;
 		__entry->sync_mode	= wbc->sync_mode;
 		__entry->cgroup_ino	= __trace_wbc_assign_cgroup(wbc);
@@ -234,8 +235,9 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 		__field(unsigned int, cgroup_ino)
 	),
 	TP_fast_assign(
-		strncpy(__entry->name,
-			wb->bdi->dev ? dev_name(wb->bdi->dev) : "(unknown)", 32);
+		strscpy_pad(__entry->name,
+			    wb->bdi->dev ? dev_name(wb->bdi->dev) :
+			    "(unknown)", 32);
 		__entry->nr_pages = work->nr_pages;
 		__entry->sb_dev = work->sb ? work->sb->s_dev : 0;
 		__entry->sync_mode = work->sync_mode;
@@ -288,7 +290,7 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 		__field(unsigned int, cgroup_ino)
 	),
 	TP_fast_assign(
-		strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
+		strscpy_pad(__entry->name, dev_name(wb->bdi->dev), 32);
 		__entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
 	),
 	TP_printk("bdi %s: cgroup_ino=%u",
@@ -310,7 +312,7 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 		__array(char, name, 32)
 	),
 	TP_fast_assign(
-		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		strscpy_pad(__entry->name, dev_name(bdi->dev), 32);
 	),
 	TP_printk("bdi %s",
 		__entry->name
@@ -335,7 +337,7 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		strscpy_pad(__entry->name, dev_name(bdi->dev), 32);
 		__entry->nr_to_write	= wbc->nr_to_write;
 		__entry->pages_skipped	= wbc->pages_skipped;
 		__entry->sync_mode	= wbc->sync_mode;
@@ -386,7 +388,7 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 	),
 	TP_fast_assign(
 		unsigned long *older_than_this = work->older_than_this;
-		strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
+		strscpy_pad(__entry->name, dev_name(wb->bdi->dev), 32);
 		__entry->older	= older_than_this ?  *older_than_this : 0;
 		__entry->age	= older_than_this ?
 				  (jiffies - *older_than_this) * 1000 / HZ : -1;
@@ -472,7 +474,7 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 	),
 
 	TP_fast_assign(
-		strlcpy(__entry->bdi, dev_name(wb->bdi->dev), 32);
+		strscpy_pad(__entry->bdi, dev_name(wb->bdi->dev), 32);
 		__entry->write_bw	= KBps(wb->write_bandwidth);
 		__entry->avg_write_bw	= KBps(wb->avg_write_bandwidth);
 		__entry->dirty_rate	= KBps(dirty_rate);
@@ -537,7 +539,7 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 
 	TP_fast_assign(
 		unsigned long freerun = (thresh + bg_thresh) / 2;
-		strlcpy(__entry->bdi, dev_name(wb->bdi->dev), 32);
+		strscpy_pad(__entry->bdi, dev_name(wb->bdi->dev), 32);
 
 		__entry->limit		= global_wb_domain.dirty_limit;
 		__entry->setpoint	= (global_wb_domain.dirty_limit +
@@ -597,8 +599,8 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name,
-		        dev_name(inode_to_bdi(inode)->dev), 32);
+		strscpy_pad(__entry->name,
+			    dev_name(inode_to_bdi(inode)->dev), 32);
 		__entry->ino		= inode->i_ino;
 		__entry->state		= inode->i_state;
 		__entry->dirtied_when	= inode->dirtied_when;
@@ -671,8 +673,8 @@ static inline unsigned int __trace_wbc_assign_cgroup(struct writeback_control *w
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name,
-			dev_name(inode_to_bdi(inode)->dev), 32);
+		strscpy_pad(__entry->name,
+			    dev_name(inode_to_bdi(inode)->dev), 32);
 		__entry->ino		= inode->i_ino;
 		__entry->state		= inode->i_state;
 		__entry->dirtied_when	= inode->dirtied_when;
-- 
1.8.3.1


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2019-07-25 17:18 [PATCH v3] writeback: fix -Wstringop-truncation warnings Qian Cai
2019-07-30 17:22 ` Jan Kara

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