On Sun, Aug 01, 2021 at 10:19:07AM -0700, Dmitry Torokhov wrote: > On Sun, Aug 01, 2021 at 09:44:33AM -0700, Kees Cook wrote: > > On Sun, Aug 01, 2021 at 05:57:32PM +0200, Len Baker wrote: > > > Hi, > > > > > > On Sun, Aug 01, 2021 at 04:00:00PM +0100, Russell King (Oracle) wrote: > > > > On Sun, Aug 01, 2021 at 04:43:16PM +0200, Len Baker wrote: > > > > > strcpy() performs no bounds checking on the destination buffer. This > > > > > could result in linear overflows beyond the end of the buffer, leading > > > > > to all kinds of misbehaviors. The safe replacement is strscpy(). > > > > > > > > > > Signed-off-by: Len Baker <len.baker@xxxxxxx> > > > > > --- > > > > > This is a task of the KSPP [1] > > > > > > > > > > [1] https://github.com/KSPP/linux/issues/88 > > > > > > > > > > drivers/input/keyboard/locomokbd.c | 2 +- > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > diff --git a/drivers/input/keyboard/locomokbd.c b/drivers/input/keyboard/locomokbd.c > > > > > index dae053596572..dbb3dc48df12 100644 > > > > > --- a/drivers/input/keyboard/locomokbd.c > > > > > +++ b/drivers/input/keyboard/locomokbd.c > > > > > @@ -254,7 +254,7 @@ static int locomokbd_probe(struct locomo_dev *dev) > > > > > locomokbd->suspend_jiffies = jiffies; > > > > > > > > > > locomokbd->input = input_dev; > > > > > - strcpy(locomokbd->phys, "locomokbd/input0"); > > > > > + strscpy(locomokbd->phys, "locomokbd/input0", sizeof(locomokbd->phys)); > > > > > > > > So if the string doesn't fit, it's fine to silently truncate it? > > > > > > I think it is better than overflow :) > > > > > > > Rather than converting every single strcpy() in the kernel to > > > > strscpy(), maybe there should be some consideration given to how the > > > > issue of a strcpy() that overflows the buffer should be handled. > > > > E.g. in the case of a known string such as the above, if it's longer > > > > than the destination, should we find a way to make the compiler issue > > > > a warning at compile time? > > > > > > Good point. I am a kernel newbie and have no experience. So this > > > question should be answered by some kernel hacker :) But I agree > > > with your proposals. > > > > > > Kees and folks: Any comments? > > > > > > Note: Kees is asked the same question in [2] > > > > > > [2] https://lore.kernel.org/lkml/20210731135957.GB1979@titan/ > > > > Hi! > > > > Sorry for the delay at looking into this. It didn't use to be a problem > > (there would always have been a compile-time warning generated for > > known-too-small cases), but that appears to have regressed when, > > ironically, strscpy() coverage was added. I've detailed it in the bug > > report: > > https://github.com/KSPP/linux/issues/88 > > > > So, bottom line: we need to fix the missing compile-time warnings for > > strcpy() and strscpy() under CONFIG_FORTIFY_SOURCE=y. > > Is it possible to have them warn always? Or that would be too many false > positives? There are actually no false positives right now (they were all fixed before FORTIFY_SOURCE landed). Enabling it by default would likely mean splitting compile-time checks from run-time checks... I'm kind of already doing this in the recent memcpy() strictness series[1], so ... maybe? I think I'd like to land the memcpy() series first, then we can revisit making it always warn. > > In the past we'd tried to add a stracpy()[1] that would only work with > > const string sources. Linus got angry[2] about API explosion, though, > > so we're mostly faced with doing the strscpy() replacements. > > I would like to have an API that would do compile-time checks and > BUILD_BUG_ON() for a few places in input drivers where we copy constant > strings. There is no reason to encumber the code with runtime checks, > and bombing out on compile instead of truncating would be nice. In theory, this is provided by CONFIG_FORTIFY_SOURCE, though a recent change broke a specific instance. I've added tests for this now to the memcpy() series, and will get it fixed in there too. > > Another idea might be to have strcpy() do the "constant strings only" > > thing, leaving strscpy() for the dynamic lengths. > > > > One thing is clear: replacing strlcpy() with strscpy() is probably the > > easiest and best first step to cleaning up the proliferation of str*() > > functions. > > OK, so the consensus is that we set this patch aside as it does not > really fix any issues (the strcpy() destination is 32 bytes and is big > enough to hold the string being copied)? I think that's fair. -Kees [1] https://lore.kernel.org/lkml/20210727205855.411487-1-keescook@xxxxxxxxxxxx/ -- Kees Cook
