From 0ef37eef83fad3542ee06db2940433ae1a92b39d Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 12 May 2026 13:33:47 +0100 Subject: [PATCH] netfs: Fix overrun check in netfs_extract_user_iter() Fix netfs_extract_user_iter() so that if iov_iter_extract_pages() overfills pages[], then those pages don't get included in the iterator constructed at the end of the function. If there was an overfill, memory corruption has already happened. Fixes: 85dd2c8ff368 ("netfs: Add a function to extract a UBUF or IOVEC into a BVEC iterator") Closes: https://sashiko.dev/#/patchset/20260427154639.180684-1-dhowells%40redhat.com Signed-off-by: David Howells Link: https://patch.msgid.link/20260512123404.719402-11-dhowells@redhat.com cc: Paulo Alcantara cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner --- fs/netfs/iterator.c | 26 +++++++++++++++++--------- 1 file changed, 17 insertions(+), 9 deletions(-) diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c index 429e4396e1b0..b375567e0520 100644 --- a/fs/netfs/iterator.c +++ b/fs/netfs/iterator.c @@ -72,20 +72,23 @@ ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len, break; } - if (ret > count) { - pr_err("get_pages rc=%zd more than %zu\n", ret, count); + if (WARN(ret > count, + "%s: extract_pages overrun %zd > %zu bytes\n", + __func__, ret, count)) { + ret = -EIO; + break; + } + + cur_npages = DIV_ROUND_UP(offset + ret, PAGE_SIZE); + if (WARN(cur_npages > max_pages - npages, + "%s: extract_pages overrun %u > %u pages\n", + __func__, npages + cur_npages, max_pages)) { + ret = -EIO; break; } count -= ret; ret += offset; - cur_npages = DIV_ROUND_UP(ret, PAGE_SIZE); - - if (npages + cur_npages > max_pages) { - pr_err("Out of bvec array capacity (%u vs %u)\n", - npages + cur_npages, max_pages); - break; - } for (i = 0; i < cur_npages; i++) { len = ret > PAGE_SIZE ? PAGE_SIZE : ret; @@ -97,6 +100,11 @@ ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len, npages += cur_npages; } + /* Note: Don't try to clean up after EIO. Either we got no pages, so + * nothing to clean up, or we got a buffer overrun, memory corruption + * and can't trust the stuff in the buffer (a WARN was emitted). + */ + if (ret < 0 && (ret == -ENOMEM || npages == 0)) { for (i = 0; i < npages; i++) unpin_user_page(bv[i].bv_page);