Messages in this thread | | | Date | Fri, 17 Jun 2022 12:41:11 -0400 | Subject | Re: [PATCH RFCv4 3/4] lib/test_printf.c: split write-beyond-buffer check in two | From | Kent Overstreet <> |
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On 6/17/22 03:15, Rasmus Villemoes wrote: > On 17/06/2021 16.17, Petr Mladek wrote: >> On Tue 2021-06-15 23:49:51, Jia He wrote: >>> From: Rasmus Villemoes <linux@rasmusvillemoes.dk> >>> >>> Before each invocation of vsnprintf(), do_test() memsets the entire >>> allocated buffer to a sentinel value. That buffer includes leading and >>> trailing padding which is never included in the buffer area handed to >>> vsnprintf (spaces merely for clarity): >>> >>> pad test_buffer pad >>> **** **************** **** >>> >>> Then vsnprintf() is invoked with a bufsize argument <= >>> BUF_SIZE. Suppose bufsize=10, then we'd have e.g. >>> >>> |pad | test_buffer |pad | >>> **** pizza0 **** ****** **** >>> A B C D E >>> >>> where vsnprintf() was given the area from B to D. >>> >>> It is obviously a bug for vsnprintf to touch anything between A and B >>> or between D and E. The former is checked for as one would expect. But >>> for the latter, we are actually a little stricter in that we check the >>> area between C and E. >>> >>> Split that check in two, providing a clearer error message in case it >>> was a genuine buffer overrun and not merely a write within the >>> provided buffer, but after the end of the generated string. >>> >>> So far, no part of the vsnprintf() implementation has had any use for >>> using the whole buffer as scratch space, but it's not unreasonable to >>> allow that, as long as the result is properly nul-terminated and the >>> return value is the right one. However, it is somewhat unusual, and >>> most %<something> won't need this, so keep the [C,D] check, but make >>> it easy for a later patch to make that part opt-out for certain tests. >> >> Excellent commit message. >> >>> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> >>> Tested-by: Jia He <justin.he@arm.com> >>> Signed-off-by: Jia He <justin.he@arm.com> >> >> Reviewed-by: Petr Mladek <pmladek@suse.com> > > Hi Petr > > It seems Justin's series got stalled, but I still think this patch makes > sense on its own (especially since another series in flight mucks about > in this area), so can you please pick it up directly? > > The lore link for the above is > https://lore.kernel.org/lkml/20210615154952.2744-4-justin.he@arm.com/ , > while my original submission is at > https://lore.kernel.org/lkml/20210615085044.1923788-1-linux@rasmusvillemoes.dk/
That patch definitely clarifies things, feel free to add my reviewed-by tag
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