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SubjectRe: [PATCH] netlink: drop (int) cast on length arg in NLMSG_OK
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From: Mike Frysinger <vapier@gentoo.org>
Date: Thu, 5 Mar 2015 00:47:08 -0500

> The NLMSG_OK macro compares three things:
> - the len arg from the user
> - a size_t: sizeof(struct nlmsghdr)
> - an int: sizeof(struct nlmsghdr) casted
> - an u32: the nlmsghdr->nlmsg_len member
>
> When building with -Wsign-compare, this macro triggers a signed compare
> warning. This is because it compares len to an int, and then compares
> it to a u32. If len is signed, we get a warning due to the last test.
> If len is unsigned, we get a warning due to the first test. Like in
> strace:
> socketutils.c:145:8: warning: comparison between signed and unsigned
> integer expressions [-Wsign-compare]
>
> Lets drop the int cast on the first sizeof. This way, once the user
> casts len to an unsigned value, everything shakes out correctly.
>
> Signed-off-by: Mike Frysinger <vapier@gentoo.org>

I don't think we can change this. If you get rid of the 'int' cast
then code is going to end up with a signed comparison for the first
test even if 'len' is signed, and that's a potential security issue.


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