[PATCH 6.18.y 1/4] dm-verity-fec: fix the size of dm_verity_fec_io::erasures

[Sasha Levin <sashal@kernel.org>]

From: Eric Biggers <ebiggers@kernel.org>

[ Upstream commit a7fca324d7d90f7b139d4d32747c83a629fdb446 ]

At most 25 entries in dm_verity_fec_io::erasures are used: the maximum
number of FEC roots plus one.  Therefore, set the array size
accordingly.  This reduces the size of dm_verity_fec_io by 912 bytes.

Note: a later commit introduces a constant DM_VERITY_FEC_MAX_ROOTS,
which allows the size to be more clearly expressed as
DM_VERITY_FEC_MAX_ROOTS + 1.  This commit just fixes the size first.

Fixes: a739ff3f543a ("dm verity: add support for forward error correction")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Stable-dep-of: 31d6e6c0ba8d ("dm-verity: fix buffer overflow in FEC calculation")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/dm-verity-fec.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-verity-fec.h b/drivers/md/dm-verity-fec.h
index ec37e607cb3f09..6f11abb3c7d972 100644
--- a/drivers/md/dm-verity-fec.h
+++ b/drivers/md/dm-verity-fec.h
@@ -15,6 +15,7 @@
 #define DM_VERITY_FEC_RSM		255
 #define DM_VERITY_FEC_MAX_RSN		253
 #define DM_VERITY_FEC_MIN_RSN		231	/* ~10% space overhead */
+#define DM_VERITY_FEC_MAX_ROOTS	(DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN)
 
 /* buffers for deinterleaving and decoding */
 #define DM_VERITY_FEC_BUF_PREALLOC	1	/* buffers to preallocate */
@@ -50,11 +51,11 @@ struct dm_verity_fec {
 /* per-bio data */
 struct dm_verity_fec_io {
 	struct rs_control *rs;	/* Reed-Solomon state */
-	int erasures[DM_VERITY_FEC_MAX_RSN];	/* erasures for decode_rs8 */
-	u8 *bufs[DM_VERITY_FEC_BUF_MAX];	/* bufs for deinterleaving */
-	unsigned int nbufs;		/* number of buffers allocated */
+	int erasures[DM_VERITY_FEC_MAX_ROOTS + 1]; /* erasures for decode_rs8 */
 	u8 *output;		/* buffer for corrected output */
 	unsigned int level;		/* recursion level */
+	unsigned int nbufs;		/* number of buffers allocated */
+	u8 *bufs[DM_VERITY_FEC_BUF_MAX];	/* bufs for deinterleaving */
 };
 
 #ifdef CONFIG_DM_VERITY_FEC
-- 
2.53.0