6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mikulas Patocka [ 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 Assisted-by: Claude:claude-opus-4-6 Cc: stable@vger.kernel.org Fixes: a739ff3f543a ("dm verity: add support for forward error correction") Reviewed-by: Sami Tolvanen Signed-off-by: Mikulas Patocka Signed-off-by: Sasha Levin --- drivers/md/dm-verity-fec.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) 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; } -- 2.53.0