From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BCD78380FDB; Wed, 29 Jul 2026 05:21:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785302504; cv=none; b=R9gwyzYcnhaqlQy+smZV4XhavB1FxQNtIPCwSbyh7CrMNK+b6mIOOspu/AeQhadDMmySW1IsosvHP6zUIow21b1t0dOw4Ma65A8LRwSzKXwwesSisMaElJ2sXT+cW4qKR64hq3HiFYTqi3wDz0OystH+rsGNOxdo1Fhi3gcao7Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785302504; c=relaxed/simple; bh=zzFjy3PR4+MOFsOiWBi2F/P7UriLMHFOQvrN7eO1Pjk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rzUu/hWptJKUcGu/cPd84Osw4Jpdr7SmaFDvA+GOKgGPMgsJflU6xwtmpfWw4w7qj5h8bWQWhR6vJvE0rk2FvSKMXfC56k38UK5GksQkIPX2/smQmk9aL2/W/8BJUWy+EPvTkUgj9/fy7SyFjnJ/pJblvmCoClaWCTQqfxjkRvY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MEFnoPwk; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MEFnoPwk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 84A681F00A3E; Wed, 29 Jul 2026 05:21:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785302502; bh=kiGQN0ud58DmLa7f+F3uKR8nB17Y9Z1laqzvPo6y+gQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=MEFnoPwkvQ7rbQXXdsBF/1MUv2cZFzbeGjAvUEDQOc6gxCNmIa7ze5tJ5OI4eitt4 MgK5uStStlgkua97ZSSCUPutMK8ABDr59F0OOB7zTdmKm+ZXv3j7yTezDebozzBRoz 6ubj9T1kLpUH9Ohhhxss6Bzcd/ndqIFGDITeQ29QfE/klzzvxiMR9TZROLbfYHyMwp M0aEJwzfDUr/GQP8ZeufGrT9ToJ1PyMTNGxqgXoERSEd7EM+JtePQafUyIEyC/dSF1 tTJz7InZMpP8zznwduZ1t4YKy7zNunaOJ0kzqVOUX8Yefo4mLyVclh467NPuNHdB2q Q++Wy2UlqhzKg== From: Eric Biggers To: stable@vger.kernel.org Cc: dm-devel@lists.linux.dev, Mikulas Patocka , Eric Biggers Subject: [PATCH 6.18 2/4] dm-verity-fec: fix reading parity bytes split across blocks (take 3) Date: Tue, 28 Jul 2026 22:19:07 -0700 Message-ID: <20260729051909.62106-3-ebiggers@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260729051909.62106-1-ebiggers@kernel.org> References: <20260729051909.62106-1-ebiggers@kernel.org> Precedence: bulk X-Mailing-List: dm-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit commit 430a05cb926f6bdf53e81460a2c3a553257f3f61 upstream. fec_decode_bufs() assumes that the parity bytes of the first RS codeword it decodes are never split across parity blocks. This assumption is false. Consider v->fec->block_size == 4096 && v->fec->roots == 17 && fio->nbufs == 1, for example. In that case, each call to fec_decode_bufs() consumes v->fec->roots * (fio->nbufs << DM_VERITY_FEC_BUF_RS_BITS) = 272 parity bytes. Considering that the parity data for each message block starts on a block boundary, the byte alignment in the parity data will iterate through 272*i mod 4096 until the 3 parity blocks have been consumed. On the 16th call (i=15), the alignment will be 4080 bytes into the first block. Only 16 bytes remain in that block, but 17 parity bytes will be needed. The code reads out-of-bounds from the parity block buffer. Fortunately this doesn't normally happen, since it can occur only for certain non-default values of fec_roots *and* when the maximum number of buffers couldn't be allocated due to low memory. For example with block_size=4096 only the following cases are affected: fec_roots=17: nbufs in [1, 3, 5, 15] fec_roots=19: nbufs in [1, 229] fec_roots=21: nbufs in [1, 3, 5, 13, 15, 39, 65, 195] fec_roots=23: nbufs in [1, 89] Regardless, fix it by refactoring how the parity blocks are read. Fixes: 6df90c02bae4 ("dm-verity FEC: Fix RS FEC repair for roots unaligned to block size (take 2)") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers Signed-off-by: Mikulas Patocka --- drivers/md/dm-verity-fec.c | 100 ++++++++++++++++--------------------- 1 file changed, 44 insertions(+), 56 deletions(-) diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c index 03e59b85132aa..a8fbf97b97517 100644 --- a/drivers/md/dm-verity-fec.c +++ b/drivers/md/dm-verity-fec.c @@ -39,36 +39,6 @@ static inline u64 fec_interleave(struct dm_verity *v, u64 offset) return offset + mod * (v->fec->rounds << v->data_dev_block_bits); } -/* - * Read error-correcting codes for the requested RS block. Returns a pointer - * to the data block. Caller is responsible for releasing buf. - */ -static u8 *fec_read_parity(struct dm_verity *v, u64 rsb, int index, - unsigned int *offset, unsigned int par_buf_offset, - struct dm_buffer **buf, unsigned short ioprio) -{ - u64 position, block, rem; - u8 *res; - - /* We have already part of parity bytes read, skip to the next block */ - if (par_buf_offset) - index++; - - position = (index + rsb) * v->fec->roots; - block = div64_u64_rem(position, v->fec->io_size, &rem); - *offset = par_buf_offset ? 0 : (unsigned int)rem; - - res = dm_bufio_read_with_ioprio(v->fec->bufio, block, buf, ioprio); - if (IS_ERR(res)) { - DMERR("%s: FEC %llu: parity read failed (block %llu): %ld", - v->data_dev->name, (unsigned long long)rsb, - (unsigned long long)block, PTR_ERR(res)); - *buf = NULL; - } - - return res; -} - /* Loop over each preallocated buffer slot. */ #define fec_for_each_prealloc_buffer(__i) \ for (__i = 0; __i < DM_VERITY_FEC_BUF_PREALLOC; __i++) @@ -116,15 +86,29 @@ 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, offset, par_buf_offset = 0; + unsigned int n, i, j, parity_pos, to_copy; uint16_t par_buf[DM_VERITY_FEC_RSM - DM_VERITY_FEC_MIN_RSN]; u8 *par, *block; + u64 parity_block; struct bio *bio = dm_bio_from_per_bio_data(io, v->ti->per_io_data_size); - par = fec_read_parity(v, rsb, block_offset, &offset, - par_buf_offset, &buf, bio->bi_ioprio); - if (IS_ERR(par)) + /* + * Compute the index of the first parity block that will be needed and + * the starting position in that block. Then read that block. + * + * io_size is always a power of 2, but roots might not be. Note that + * when it's not, a codeword's parity bytes can span a block boundary. + */ + parity_block = (rsb + block_offset) * v->fec->roots; + parity_pos = parity_block & (v->fec->io_size - 1); + parity_block >>= v->data_dev_block_bits; + par = dm_bufio_read_with_ioprio(v->fec->bufio, parity_block, &buf, + bio->bi_ioprio); + if (IS_ERR(par)) { + DMERR("%s: FEC %llu: parity read failed (block %llu): %ld", + v->data_dev->name, rsb, parity_block, PTR_ERR(par)); return PTR_ERR(par); + } /* * Decode the RS blocks we have in bufs. Each RS block results in @@ -132,8 +116,32 @@ static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_io *io, */ fec_for_each_buffer_rs_block(fio, n, i) { block = fec_buffer_rs_block(v, fio, n, i); - for (j = 0; j < v->fec->roots - par_buf_offset; j++) - par_buf[par_buf_offset + j] = par[offset + j]; + + /* + * Copy the next 'roots' parity bytes to 'par_buf', reading + * another parity block if needed. + */ + to_copy = min(v->fec->io_size - parity_pos, v->fec->roots); + for (j = 0; j < to_copy; j++) + par_buf[j] = par[parity_pos++]; + if (to_copy < v->fec->roots) { + parity_block++; + parity_pos = 0; + + dm_bufio_release(buf); + par = dm_bufio_read_with_ioprio(v->fec->bufio, + parity_block, &buf, + bio->bi_ioprio); + if (IS_ERR(par)) { + DMERR("%s: FEC %llu: parity read failed (block %llu): %ld", + v->data_dev->name, rsb, parity_block, + PTR_ERR(par)); + return PTR_ERR(par); + } + for (; j < v->fec->roots; j++) + par_buf[j] = par[parity_pos++]; + } + /* Decode an RS block using Reed-Solomon */ res = decode_rs8(fio->rs, block, par_buf, v->fec->rsn, NULL, neras, fio->erasures, 0, NULL); @@ -148,26 +156,6 @@ static int fec_decode_bufs(struct dm_verity *v, struct dm_verity_io *io, block_offset++; if (block_offset >= 1 << v->data_dev_block_bits) goto done; - - /* Read the next block when we run out of parity bytes */ - offset += (v->fec->roots - par_buf_offset); - /* Check if parity bytes are split between blocks */ - if (offset < v->fec->io_size && (offset + v->fec->roots) > v->fec->io_size) { - par_buf_offset = v->fec->io_size - offset; - for (j = 0; j < par_buf_offset; j++) - par_buf[j] = par[offset + j]; - offset += par_buf_offset; - } else - par_buf_offset = 0; - - if (offset >= v->fec->io_size) { - dm_bufio_release(buf); - - par = fec_read_parity(v, rsb, block_offset, &offset, - par_buf_offset, &buf, bio->bi_ioprio); - if (IS_ERR(par)) - return PTR_ERR(par); - } } done: r = corrected; -- 2.55.0