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net/ipv4: Replace one-element array with flexible-array member

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[ Upstream commit 2d3e5caf96b9449af951e63476657acd759c1a30 ]

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Use an anonymous union with a couple of anonymous structs in order to
keep userspace unchanged:

$ pahole -C ip_msfilter net/ipv4/ip_sockglue.o
struct ip_msfilter {
	union {
		struct {
			__be32     imsf_multiaddr_aux;   /*     0     4 */
			__be32     imsf_interface_aux;   /*     4     4 */
			__u32      imsf_fmode_aux;       /*     8     4 */
			__u32      imsf_numsrc_aux;      /*    12     4 */
			__be32     imsf_slist[1];        /*    16     4 */
		};                                       /*     0    20 */
		struct {
			__be32     imsf_multiaddr;       /*     0     4 */
			__be32     imsf_interface;       /*     4     4 */
			__u32      imsf_fmode;           /*     8     4 */
			__u32      imsf_numsrc;          /*    12     4 */
			__be32     imsf_slist_flex[0];   /*    16     0 */
		};                                       /*     0    16 */
	};                                               /*     0    20 */

	/* size: 20, cachelines: 1, members: 1 */
	/* last cacheline: 20 bytes */
};

Also, refactor the code accordingly and make use of the struct_size()
and flex_array_size() helpers.

This helps with the ongoing efforts to globally enable -Warray-bounds
and get us closer to being able to tighten the FORTIFY_SOURCE routines
on memcpy().

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 5c3be3e0eb44 ("ipmr: fix incorrect parameter validation in the ip_mroute_getsockopt() function")
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Gustavo A. R. Silva
2021-07-31 12:08:30 -05:00
committed by Sasha Levin
parent c805987631
commit 1ebd0d898f
3 changed files with 30 additions and 18 deletions
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21
include/uapi/linux/in.h
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@@ -190,11 +190,22 @@ struct ip_mreq_source {
};
struct ip_msfilter {
__be32 imsf_multiaddr;
__be32 imsf_interface;
__u32 imsf_fmode;
__u32 imsf_numsrc;
__be32 imsf_slist[1];
union {
struct {
__be32 imsf_multiaddr_aux;
__be32 imsf_interface_aux;
__u32 imsf_fmode_aux;
__u32 imsf_numsrc_aux;
__be32 imsf_slist[1];
};
struct {
__be32 imsf_multiaddr;
__be32 imsf_interface;
__u32 imsf_fmode;
__u32 imsf_numsrc;
__be32 imsf_slist_flex[];
};
};
};
#define IP_MSFILTER_SIZE(numsrc) \