[PATCH 3/4] textsearch: align ts_state.cb like skb->cb

[Bernard Ladenthin]

struct ts_state carries a 48-byte control buffer that callers cast to
their own state structure. lib/textsearch.c casts it to struct
ts_linear_state. net/core/skbuff.c casts it to struct skb_seq_state via
TS_SKB_CB(). Both contain pointers and so need 8-byte alignment on 64-bit.

cb sits at offset 4, right after the unsigned int offset field, and struct
ts_state itself has only 4-byte alignment. Any allocation aligned to 8 or
more therefore places cb on a 4-mod-8 address. kmalloc() guarantees at
least ARCH_KMALLOC_MINALIGN, which is 8 or larger, so a heap-allocated
ts_state has a misaligned cb every time. For a stack-allocated one it
depends on where the compiler happens to put it.

No in-tree caller is affected today. The only struct ts_state is a stack
local in skb_find_text(). The cast is undefined behaviour regardless, and
on architectures without efficient unaligned access it is a trap for
whoever allocates one of these on the heap.

struct sk_buff already marks its cb[48] __aligned(8) for exactly this
reason. Do the same here.

Signed-off-by: Bernard Ladenthin <bernard.ladenthin@xxxxxxxxx>
---
This is my first kernel submission. Corrections on anything I got wrong in
the process are welcome.

 include/linux/textsearch.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/textsearch.h b/include/linux/textsearch.h
index 4933777404d6..e117f9c9de59 100644
--- a/include/linux/textsearch.h
+++ b/include/linux/textsearch.h
@@ -23,7 +23,7 @@ struct ts_config;
 struct ts_state
 {
 	unsigned int		offset;
-	char			cb[48];
+	char			cb[48] __aligned(8);
 };
 
 /**
-- 
2.49.0.windows.1