Messages in this thread | | | Date | Fri, 14 Feb 2020 18:36:50 -0500 | From | Sasha Levin <> | Subject | Re: [PATCH AUTOSEL 4.4 080/100] char: hpet: Use flexible-array member |
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On Fri, Feb 14, 2020 at 09:43:14AM -0800, Eric Biggers wrote: >On Fri, Feb 14, 2020 at 11:24:04AM -0500, Sasha Levin wrote: >> From: "Gustavo A. R. Silva" <gustavo@embeddedor.com> >> >> [ Upstream commit 987f028b8637cfa7658aa456ae73f8f21a7a7f6f ] >> >> Old code in the kernel uses 1-byte and 0-byte arrays to indicate the >> presence of a "variable length array": >> >> struct something { >> int length; >> u8 data[1]; >> }; >> >> struct something *instance; >> >> instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL); >> instance->length = size; >> memcpy(instance->data, source, size); >> >> There is also 0-byte arrays. Both cases pose confusion for things like >> sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism >> to declare variable-length types such as the one above is a flexible array >> member[2] which need to be the last member of a structure and empty-sized: >> >> struct something { >> int stuff; >> u8 data[]; >> }; >> >> Also, by making use of the mechanism above, we will get a compiler warning >> in case the flexible array does not occur last in the structure, which >> will help us prevent some kind of undefined behavior bugs from being >> unadvertenly introduced[3] to the codebase from now on. >> >> [1] https://github.com/KSPP/linux/issues/21 >> [2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html >> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") >> >> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> >> Link: https://lore.kernel.org/r/20200120235326.GA29231@embeddedor.com >> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> >> Signed-off-by: Sasha Levin <sashal@kernel.org> >> --- >> drivers/char/hpet.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c >> index 5b38d7a8202a1..38c2ae93ce492 100644 >> --- a/drivers/char/hpet.c >> +++ b/drivers/char/hpet.c >> @@ -112,7 +112,7 @@ struct hpets { >> unsigned long hp_delta; >> unsigned int hp_ntimer; >> unsigned int hp_which; >> - struct hpet_dev hp_dev[1]; >> + struct hpet_dev hp_dev[]; >> }; >> > >Umm, why are you backporting this without the commit that fixes it? Does your
mhm, for some reason it failed to apply to 4.19 and older. I can look at that.
>AUTOSEL process really still not pay attention to Fixes tags? They are there >for a reason.
Yes, it looks at the Fixes tag, thank you for the explanation.
>And for that matter, why are you backporting it all, given that this is a >cleanup and not a fix?
If I recall correctly CONFIG_FORTIFY_SOURCE=y results in user visible warnings, which we try to fix in the stable kernel.
-- Thanks, Sasha
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