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

[David Laight <David.Laight@ACULAB.COM>]

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

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