Re: [PATCH] netlink: drop (int) cast on length arg in NLMSG_OK
From: Mike Frysinger 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 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 linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] netlink: drop (int) cast on length arg in NLMSG_OK
From: Mike Frysinger vap...@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 vap...@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 linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH] netlink: drop (int) cast on length arg in NLMSG_OK
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
---
include/uapi/linux/netlink.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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)))
--
2.3.1
--
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[PATCH] netlink: drop (int) cast on length arg in NLMSG_OK
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 vap...@gentoo.org
---
include/uapi/linux/netlink.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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)))
--
2.3.1
--
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