6.12-stable review patch. If anyone has any objections, please let me know.
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From: Dominique Martinet asmadeus@codewreck.org
commit 808471ddb0fa785559c3e7aee59be20a13b46ef5 upstream.
It's apparently possible to get an iov advanced all the way up to the end of the current page we're looking at, e.g.
(gdb) p *iter $24 = {iter_type = 4 '\004', nofault = false, data_source = false, iov_offset = 4096, {__ubuf_iovec = { iov_base = 0xffff88800f5bc000, iov_len = 655}, {{__iov = 0xffff88800f5bc000, kvec = 0xffff88800f5bc000, bvec = 0xffff88800f5bc000, folioq = 0xffff88800f5bc000, xarray = 0xffff88800f5bc000, ubuf = 0xffff88800f5bc000}, count = 655}}, {nr_segs = 2, folioq_slot = 2 '\002', xarray_start = 2}}
Where iov_offset is 4k with 4k-sized folios
This should have been fine because we're only in the 2nd slot and there's another one after this, but iterate_folioq should not try to map a folio that skips the whole size, and more importantly part here does not end up zero (because 'PAGE_SIZE - skip % PAGE_SIZE' ends up PAGE_SIZE and not zero..), so skip forward to the "advance to next folio" code
Link: https://lkml.kernel.org/r/20250813-iot_iter_folio-v3-0-a0ffad2b665a@codewrec... Link: https://lkml.kernel.org/r/20250813-iot_iter_folio-v3-1-a0ffad2b665a@codewrec... Signed-off-by: Dominique Martinet asmadeus@codewreck.org Fixes: db0aa2e9566f ("mm: Define struct folio_queue and ITER_FOLIOQ to handle a sequence of folios") Reported-by: Maximilian Bosch maximilian@mbosch.me Reported-by: Ryan Lahfa ryan@lahfa.xyz Reported-by: Christian Theune ct@flyingcircus.io Reported-by: Arnout Engelen arnout@bzzt.net Link: https://lkml.kernel.org/r/D4LHHUNLG79Y.12PI0X6BEHRHW@mbosch.me/ Acked-by: David Howells dhowells@redhat.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Christian Brauner brauner@kernel.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: stable@vger.kernel.org [6.12+] Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/iov_iter.h | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-)
diff --git a/include/linux/iov_iter.h b/include/linux/iov_iter.h index c4aa58032faf..f9a17fbbd398 100644 --- a/include/linux/iov_iter.h +++ b/include/linux/iov_iter.h @@ -160,7 +160,7 @@ size_t iterate_folioq(struct iov_iter *iter, size_t len, void *priv, void *priv2
do { struct folio *folio = folioq_folio(folioq, slot); - size_t part, remain, consumed; + size_t part, remain = 0, consumed; size_t fsize; void *base;
@@ -168,14 +168,16 @@ size_t iterate_folioq(struct iov_iter *iter, size_t len, void *priv, void *priv2 break;
fsize = folioq_folio_size(folioq, slot); - base = kmap_local_folio(folio, skip); - part = umin(len, PAGE_SIZE - skip % PAGE_SIZE); - remain = step(base, progress, part, priv, priv2); - kunmap_local(base); - consumed = part - remain; - len -= consumed; - progress += consumed; - skip += consumed; + if (skip < fsize) { + base = kmap_local_folio(folio, skip); + part = umin(len, PAGE_SIZE - skip % PAGE_SIZE); + remain = step(base, progress, part, priv, priv2); + kunmap_local(base); + consumed = part - remain; + len -= consumed; + progress += consumed; + skip += consumed; + } if (skip >= fsize) { skip = 0; slot++;