From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Eric Biggers <ebiggers@kernel.org>,
Mikulas Patocka <mpatocka@redhat.com>,
Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.18.y 3/4] dm-verity-fec: replace {MAX,MIN}_RSN with {MIN,MAX}_ROOTS
Date: Mon, 27 Jul 2026 17:00:10 -0400 [thread overview]
Message-ID: <20260727210011.1929439-3-sashal@kernel.org> (raw)
In-Reply-To: <20260727210011.1929439-1-sashal@kernel.org>
From: Eric Biggers <ebiggers@kernel.org>
[ Upstream commit 82fbd6a3e29a329d439690cd7ccc4162c9cd8db6 ]
Every time DM_VERITY_FEC_{MAX,MIN}_RSN are used, they are subtracted
from DM_VERITY_FEC_RSM to get the bounds on the number of roots.
Therefore, replace these with {MIN,MAX}_ROOTS constants which are more
directly useful. (Note the inversion, where MAX_RSN maps to MIN_ROOTS
and MIN_RSN maps to MAX_ROOTS.) No functional change.
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.c | 6 +++---
drivers/md/dm-verity-fec.h | 5 ++---
2 files changed, 5 insertions(+), 6 deletions(-)
diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c
index a8fbf97b97517f..cebcc8fd25d700 100644
--- a/drivers/md/dm-verity-fec.c
+++ b/drivers/md/dm-verity-fec.c
@@ -87,7 +87,7 @@ static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_io *io,
int r, corrected = 0, res;
struct dm_buffer *buf;
unsigned int n, i, j, parity_pos, to_copy;
- uint16_t par_buf[DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN];
+ uint16_t par_buf[DM_VERITY_FEC_MAX_ROOTS];
u8 *par, *block;
u64 parity_block;
struct bio *bio = dm_bio_from_per_bio_data(io, v->ti->per_io_data_size);
@@ -605,8 +605,8 @@ int verity_fec_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
} else if (!strcasecmp(arg_name, DM_VERITY_OPT_FEC_ROOTS)) {
if (sscanf(arg_value, "%hhu%c", &num_c, &dummy) != 1 || !num_c ||
- num_c < (DM_VERITY_FEC_RSM - DM_VERITY_FEC_MAX_RSN) ||
- num_c > (DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN)) {
+ num_c < DM_VERITY_FEC_MIN_ROOTS ||
+ num_c > DM_VERITY_FEC_MAX_ROOTS) {
ti->error = "Invalid " DM_VERITY_OPT_FEC_ROOTS;
return -EINVAL;
}
diff --git a/drivers/md/dm-verity-fec.h b/drivers/md/dm-verity-fec.h
index 6f11abb3c7d972..178ecdddbbd310 100644
--- a/drivers/md/dm-verity-fec.h
+++ b/drivers/md/dm-verity-fec.h
@@ -13,9 +13,8 @@
/* Reed-Solomon(M, N) parameters */
#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)
+#define DM_VERITY_FEC_MIN_ROOTS 2 /* RS(255, 253): ~0.8% space overhead */
+#define DM_VERITY_FEC_MAX_ROOTS 24 /* RS(255, 231): ~10% space overhead */
/* buffers for deinterleaving and decoding */
#define DM_VERITY_FEC_BUF_PREALLOC 1 /* buffers to preallocate */
--
2.53.0
next prev parent reply other threads:[~2026-07-27 21:00 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-20 15:19 FAILED: patch "[PATCH] dm-verity: fix buffer overflow in FEC calculation" failed to apply to 6.18-stable tree gregkh
2026-07-27 21:00 ` [PATCH 6.18.y 1/4] dm-verity-fec: fix the size of dm_verity_fec_io::erasures Sasha Levin
2026-07-27 21:00 ` [PATCH 6.18.y 2/4] dm-verity-fec: fix reading parity bytes split across blocks (take 3) Sasha Levin
2026-07-27 21:00 ` Sasha Levin [this message]
2026-07-27 21:00 ` [PATCH 6.18.y 4/4] dm-verity: fix buffer overflow in FEC calculation Sasha Levin
2026-07-27 21:09 ` [PATCH 6.18.y 1/4] dm-verity-fec: fix the size of dm_verity_fec_io::erasures Eric Biggers
2026-07-27 21:21 ` Eric Biggers
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