| Message ID | 1425534428-24182-1-git-send-email-vapier@gentoo.org |
|---|---|
| State | Deferred, archived |
| Delegated to: | David Miller |
| Headers | show |
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. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h index 1a85940..3eb4e24 100644 --- a/include/uapi/linux/netlink.h +++ b/include/uapi/linux/netlink.h @@ -84,7 +84,7 @@ struct nlmsghdr { #define NLMSG_DATA(nlh) ((void*)(((char*)nlh) + NLMSG_LENGTH(0))) #define NLMSG_NEXT(nlh,len) ((len) -= NLMSG_ALIGN((nlh)->nlmsg_len), \ (struct nlmsghdr*)(((char*)(nlh)) + NLMSG_ALIGN((nlh)->nlmsg_len))) -#define NLMSG_OK(nlh,len) ((len) >= (int)sizeof(struct nlmsghdr) && \ +#define NLMSG_OK(nlh,len) ((len) >= sizeof(struct nlmsghdr) && \ (nlh)->nlmsg_len >= sizeof(struct nlmsghdr) && \ (nlh)->nlmsg_len <= (len)) #define NLMSG_PAYLOAD(nlh,len) ((nlh)->nlmsg_len - NLMSG_SPACE((len)))
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> --- include/uapi/linux/netlink.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)