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Wed, 14 Oct 2026 23:19:23 -0700 (PDT) Received: from ancienth-X870E-Nova-WiFi ([125.186.72.2]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ac9461d71esm2669111a91.7.2026.10.14.23.19.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Oct 2026 23:19:22 -0700 (PDT) From: Daehyeon Ko <4ncienth@gmail.com> To: Alexander Viro , Andrew Morton , Jens Axboe Cc: Keith Busch , Hannes Reinecke , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Daehyeon Ko <4ncienth@gmail.com> Subject: [PATCH v2] iov_iter: validate extracted segment for bvec alignment Date: Thu, 15 Oct 2026 15:19:07 +0900 Message-ID: <20261015061907.2713943-1-4ncienth@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit iov_iter_extract_bvecs() validates iter_iov_addr() and iter_iov_len() before iov_iter_extract_pages() selects the first nonempty segment and limits it by iter->count. The checks can therefore cover a different range after a leading empty segment or iov_iter_truncate(). An unprivileged O_DIRECT preadv() reproduced the empty-segment case: an aligned empty segment followed by a misaligned one completed 4096 bytes instead of returning -EINVAL. A truncated iterator has the same mismatch when its full segment length is aligned but its remaining count is not. Bound the normal fast-path length by iter->count. Keep first_iovec_segment() for leading empty segments so validation covers the remaining portion of the segment available for extraction. Closes: https://lore.kernel.org/r/20261012065520.1089147-1-4ncienth@gmail.com Fixes: 14b007e17881 ("block: validate user space vectors during extraction") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Daehyeon Ko <4ncienth@gmail.com> --- Changes in v2: - Bound the normal fast-path length by iter->count while retaining first_iovec_segment() for leading empty segments. - Cover the truncated-iterator case raised by Andrew Morton and Sashiko. v1: https://lore.kernel.org/r/20261012065520.1089147-1-4ncienth@gmail.com lib/iov_iter.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 2072c04e99d052..d21082fb251bf7 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -1022,7 +1022,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i, return maxsize; } -/* must be done on non-empty ITER_UBUF or ITER_IOVEC one */ +/* must be used on a non-empty ITER_UBUF, ITER_IOVEC or ITER_KVEC */ static unsigned long first_iovec_segment(const struct iov_iter *i, size_t *size) { size_t skip; @@ -1938,8 +1938,13 @@ ssize_t iov_iter_extract_bvecs(struct iov_iter *iter, struct bio_vec *bv, iter_is_iovec(iter) || iov_iter_is_kvec(iter))) { unsigned long start = (unsigned long)iter_iov_addr(iter); + size_t seg_size = min(iter_iov_len(iter), iter->count); - if ((start | iter_iov_len(iter)) & mem_align_mask) + if (unlikely(!seg_size && iter->count)) { + seg_size = iter->count; + start = first_iovec_segment(iter, &seg_size); + } + if ((start | seg_size) & mem_align_mask) return -EINVAL; } else if (iov_iter_alignment(iter) & mem_align_mask) { return -EINVAL; base-commit: 72d3fcf802c45d00b300f25b848a93c3a2bd7c7e -- 2.55.0