This is a note to let you know that I've just added the patch titled
dm-verity: fix buffer overflow in FEC calculation
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dm-verity-fix-buffer-overflow-in-fec-calculation.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
commit e7a3e9c3804cc846b6a9b7303d74dd9a6da1c8f5
Author: Mikulas Patocka <[email protected]>
Date: Wed Jul 1 18:13:50 2026 +0200
dm-verity: fix buffer overflow in FEC calculation
[ Upstream commit 31d6e6c0ba8d5a7bd59660035a089307100c5e8e ]
There's a buffer overflow in dm-verity-fec:
if (neras && *neras <= v->fec->roots)
fio->erasures[(*neras)++] = i;
This allows *neras to reach roots + 1 (the post-increment pushes it past
roots). This value is then passed as no_eras to decode_rs8(). Inside the
RS decoder (lib/reed_solomon/decode_rs.c:113-121), the erasure locator
polynomial loop writes lambda[j] where j can reach nroots + 1 — one
element past the end of lambda[] (which is sized nroots + 1, valid
indices 0..nroots). The out-of-bounds write lands on syn[0], corrupting
the syndrome buffer.
Signed-off-by: Mikulas Patocka <[email protected]>
Assisted-by: Claude:claude-opus-4-6
Cc: [email protected]
Fixes: a739ff3f543a ("dm verity: add support for forward error correction")
Reviewed-by: Sami Tolvanen <[email protected]>
Signed-off-by: Mikulas Patocka <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c
index 5073c93cf962c..a9e3d44980862 100644
--- a/drivers/md/dm-verity-fec.c
+++ b/drivers/md/dm-verity-fec.c
@@ -261,7 +261,7 @@ static int fec_read_bufs(struct dm_verity *v, struct
dm_verity_io *io,
(unsigned long long)block, PTR_ERR(bbuf));
/* assume the block is corrupted */
- if (neras && *neras <= v->fec->roots)
+ if (neras && *neras < v->fec->roots)
fio->erasures[(*neras)++] = i;
continue;
@@ -279,7 +279,7 @@ static int fec_read_bufs(struct dm_verity *v, struct
dm_verity_io *io,
* skip if we have already found the theoretical
* maximum number (i.e. fec->roots) of erasures
*/
- if (neras && *neras <= v->fec->roots &&
+ if (neras && *neras < v->fec->roots &&
fec_is_erasure(v, io, want_digest, bbuf))
fio->erasures[(*neras)++] = i;
}
