Re: [Linux-kernel-mentees] [PATCH] checkpatch: add a new check for strcpy/strlcpy uses

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

From: Joe Perches
> Sent: 05 January 2021 08:44
> 
> On Tue, 2021-01-05 at 13:53 +0530, Dwaipayan Ray wrote:
> > strcpy() performs no bounds checking on the destination buffer.
> > This could result in linear overflows beyond the end of the buffer.
> >
> > strlcpy() reads the entire source buffer first. This read
> > may exceed the destination size limit. This can be both inefficient
> > and lead to linear read overflows.
> >
> > The safe replacement to both of these is to use strscpy() instead.
> > Add a new checkpatch warning which alerts the user on finding usage of
> > strcpy() or strlcpy().
> 
> I do not believe that strscpy is preferred over strcpy.
> 
> When the size of the output buffer is known to be larger
> than the input, strcpy is faster.
> 
> There are about 2k uses of strcpy.
> Is there a use where strcpy use actually matters?
> I don't know offhand...
> 
> But I believe compilers do not optimize away the uses of strscpy
> to a simple memcpy like they do for strcpy with a const from
> 
> 	strcpy(foo, "bar");

It ought to be possible to convert:
	strscpy(foo, "bar", constant_sz)
to a memcpy() within the .h file.

Similarly it should be possible to error
	strcpy(foo, "bar")
Unless foo is large enough and "bar" is constant.

After all with a length check
	strcpy(foo, "bar")
is actually safer than
	strspy(foo, "bar", sizeof foo)
because there is less room for error.

	David

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