[PATCH v2] writeback: fix -Wstringop-truncation warnings

[PATCH v2] writeback: fix -Wstringop-truncation warnings

[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>
---

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 | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index aa7f3aeac740..41092d63a8de 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -66,8 +66,10 @@
 	),
 
 	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 +112,8 @@
 		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 +192,8 @@ 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 +236,9 @@ 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 +291,7 @@ 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 +313,7 @@ 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 +338,7 @@ 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 +389,7 @@ 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 +475,7 @@ 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 +540,7 @@ 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 +600,8 @@ 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 +674,8 @@ 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

RE: [PATCH v2] writeback: fix -Wstringop-truncation warnings

[David Laight]

From: Qian Cai
> Sent: 25 July 2019 15:39
> 
> 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>
> ---
> 
> 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 | 39 +++++++++++++++++++++------------------
>  1 file changed, 21 insertions(+), 18 deletions(-)
> 
> diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
> index aa7f3aeac740..41092d63a8de 100644
> --- a/include/trace/events/writeback.h
> +++ b/include/trace/events/writeback.h
> @@ -66,8 +66,10 @@
>  	),
> 
>  	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);

Shouldn't the 32 be 'sizeof (something)' ??

Oh, and a horrid line break.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH v2] writeback: fix -Wstringop-truncation warnings

[Qian Cai]

On Thu, 2019-07-25 at 15:04 +0000, David Laight wrote:
> From: Qian Cai
> > Sent: 25 July 2019 15:39
> > 
> > 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>
> > ---
> > 
> > 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 | 39 +++++++++++++++++++++--------------
> > ----
> >  1 file changed, 21 insertions(+), 18 deletions(-)
> > 
> > diff --git a/include/trace/events/writeback.h
> > b/include/trace/events/writeback.h
> > index aa7f3aeac740..41092d63a8de 100644
> > --- a/include/trace/events/writeback.h
> > +++ b/include/trace/events/writeback.h
> > @@ -66,8 +66,10 @@
> >  	),
> > 
> >  	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);
> 
> Shouldn't the 32 be 'sizeof (something)' ??

Maybe could do a sizeof(__entry->name) as it is defined as,

	TP_STRUCT__entry (
		__array(char, name, 32)
		__field(unsigned long, ino)
		__field(pgoff_t, index)

But, that might be a follow-up patch and does not seem belong here.

> 
> Oh, and a horrid line break.

That line is too long needs to break up. Open up to suggestions though.

Re: [PATCH v2] writeback: fix -Wstringop-truncation warnings

[Joe Perches]

On Thu, 2019-07-25 at 11:50 -0400, Qian Cai wrote:

> > > diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
[]
> > > @@ -66,8 +66,10 @@
> > >  	),
> > > 
> > >  	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);
> > 
> > Shouldn't the 32 be 'sizeof (something)' ??
> 
> Maybe could do a sizeof(__entry->name) as it is defined as,
> 
> 	TP_STRUCT__entry (
> 		__array(char, name, 32)
> 		__field(unsigned long, ino)
> 		__field(pgoff_t, index)
> 
> But, that might be a follow-up patch and does not seem belong here.

stracpy_pad would work one day.