From: Geert Uytterhoeven <geert@linux-m68k.org>

Date: Fri, 20 Dec 2019 14:31:40 +0100

Subject: net: dst: Force 4-byte alignment of dst_metrics

Git-commit: 258a980d1ec23e2c786e9536a7dd260bea74bae6

Patch-mainline: 5.5-rc3

References: networking-stable-19_12_28

When storing a pointer to a dst_metrics structure in dst_entry._metrics,

two flags are added in the least significant bits of the pointer value.

Hence this assumes all pointers to dst_metrics structures have at least

4-byte alignment.

However, on m68k, the minimum alignment of 32-bit values is 2 bytes, not

4 bytes.  Hence in some kernel builds, dst_default_metrics may be only

2-byte aligned, leading to obscure boot warnings like:

    WARNING: CPU: 0 PID: 7 at lib/refcount.c:28 refcount_warn_saturate+0x44/0x9a

    refcount_t: underflow; use-after-free.

    Modules linked in:

    CPU: 0 PID: 7 Comm: ksoftirqd/0 Tainted: G        W         5.5.0-rc2-atari-01448-g114a1a1038af891d-dirty #261

    Stack from 10835e6c:

	    10835e6c 0038134f 00023fa6 00394b0f 0000001c 00000009 00321560 00023fea

	    00394b0f 0000001c 001a70f8 00000009 00000000 10835eb4 00000001 00000000

	    04208040 0000000a 00394b4a 10835ed4 00043aa8 001a70f8 00394b0f 0000001c

	    00000009 00394b4a 0026aba8 003215a4 00000003 00000000 0026d5a8 00000001

	    003215a4 003a4361 003238d6 000001f0 00000000 003215a4 10aa3b00 00025e84

	    003ddb00 10834000 002416a8 10aa3b00 00000000 00000080 000aa038 0004854a

    Call Trace: [<00023fa6>] __warn+0xb2/0xb4

     [<00023fea>] warn_slowpath_fmt+0x42/0x64

     [<001a70f8>] refcount_warn_saturate+0x44/0x9a

     [<00043aa8>] printk+0x0/0x18

     [<001a70f8>] refcount_warn_saturate+0x44/0x9a

     [<0026aba8>] refcount_sub_and_test.constprop.73+0x38/0x3e

     [<0026d5a8>] ipv4_dst_destroy+0x5e/0x7e

     [<00025e84>] __local_bh_enable_ip+0x0/0x8e

     [<002416a8>] dst_destroy+0x40/0xae

Fix this by forcing 4-byte alignment of all dst_metrics structures.

Fixes: e5fd387ad5b30ca3 ("ipv6: do not overwrite inetpeer metrics prematurely")

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Jiri Slaby <jslaby@suse.cz>

---

 include/net/dst.h |    2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/net/dst.h

+++ b/include/net/dst.h

@@ -108,7 +108,7 @@ struct dst_entry {

 struct dst_metrics {

 	u32		metrics[RTAX_MAX];

 	atomic_t	refcnt;

-};

+} __aligned(4);		/* Low pointer bits contain DST_METRICS_FLAGS */

 extern const struct dst_metrics dst_default_metrics;

 u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old);