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uapi/if_ether.h: move __UAPI_DEF_ETHHDR libc define

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This fixes a compile problem of some user space applications by not
including linux/libc-compat.h in uapi/if_ether.h.

linux/libc-compat.h checks which "features" the header files, included
from the libc, provide to make the Linux kernel uapi header files only
provide no conflicting structures and enums. If a user application mixes
kernel headers and libc headers it could happen that linux/libc-compat.h
gets included too early where not all other libc headers are included
yet. Then the linux/libc-compat.h would not prevent all the
redefinitions and we run into compile problems.
This patch removes the include of linux/libc-compat.h from
uapi/if_ether.h to fix the recently introduced case, but not all as this
is more or less impossible.

It is no problem to do the check directly in the if_ether.h file and not
in libc-compat.h as this does not need any fancy glibc header detection
as glibc never provided struct ethhdr and should define
__UAPI_DEF_ETHHDR by them self when they will provide this.

The following test program did not compile correctly any more:

#include <linux/if_ether.h>
#include <netinet/in.h>
#include <linux/in.h>

int main(void)
{
	return 0;
}

Fixes: 6926e041a892 ("uapi/if_ether.h: prevent redefinition of struct ethhdr")
Reported-by: Guillaume Nault <g.nault@alphalink.fr>
Cc: <stable@vger.kernel.org> # 4.15
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Hauke Mehrtens 2018-02-12 23:59:51 +01:00 committed by David S. Miller
parent 07a2e1cf39
commit da360299b6
2 changed files with 5 additions and 7 deletions
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6
include/uapi/linux/if_ether.h
View File

@ -23,7 +23,6 @@
#define _UAPI_LINUX_IF_ETHER_H
#include <linux/types.h>
#include <linux/libc-compat.h>
/*
* IEEE 802.3 Ethernet magic constants. The frame sizes omit the preamble
@ -151,6 +150,11 @@
* This is an Ethernet frame header.
*/
/* allow libcs like musl to deactivate this, glibc does not implement this. */
#ifndef __UAPI_DEF_ETHHDR
#define __UAPI_DEF_ETHHDR 1
#endif
#if __UAPI_DEF_ETHHDR
struct ethhdr {
unsigned char h_dest[ETH_ALEN]; /* destination eth addr */

6
include/uapi/linux/libc-compat.h
View File

@ -264,10 +264,4 @@
#endif /* __GLIBC__ */
/* Definitions for if_ether.h */
/* allow libcs like musl to deactivate this, glibc does not implement this. */
#ifndef __UAPI_DEF_ETHHDR
#define __UAPI_DEF_ETHHDR 1
#endif
#endif /* _UAPI_LIBC_COMPAT_H */