On Tue, Jul 29, 2025 at 08:53:02PM +0200, Bernard Metzler wrote:

On 29.07.2025 14:03, Pedro Falcato wrote:

...

Ever since commit c2ff29e99a76 ("siw: Inline do_tcp_sendpages()"), we have been doing this:

static int siw_tcp_sendpages(struct socket *s, struct page **page, int offset, size_t size) [...] /* Calculate the number of bytes we need to push, for this page * specifically */ size_t bytes = min_t(size_t, PAGE_SIZE - offset, size); /* If we can't splice it, then copy it in, as normal */ if (!sendpage_ok(page[i])) msg.msg_flags &= ~MSG_SPLICE_PAGES; /* Set the bvec pointing to the page, with len $bytes */ bvec_set_page(&bvec, page[i], bytes, offset); /* Set the iter to $size, aka the size of the whole sendpages (!!!) */ iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size); try_page_again: lock_sock(sk); /* Sendmsg with $size size (!!!) */ rv = tcp_sendmsg_locked(sk, &msg, size);

This means we've been sending oversized iov_iters and tcp_sendmsg calls for a while. This has a been a benign bug because sendpage_ok() always returned true. With the recent slab allocator changes being slowly introduced into next (that disallow sendpage on large kmalloc allocations), we have recently hit out-of-bounds crashes, due to slight differences in iov_iter behavior between the MSG_SPLICE_PAGES and "regular" copy paths:

(MSG_SPLICE_PAGES) skb_splice_from_iter iov_iter_extract_pages iov_iter_extract_bvec_pages uses i->nr_segs to correctly stop in its tracks before OoB'ing everywhere skb_splice_from_iter gets a "short" read

(!MSG_SPLICE_PAGES) skb_copy_to_page_nocache copy=iov_iter_count [...] copy_from_iter /* this doesn't help */ if (unlikely(iter->count < len)) len = iter->count; iterate_bvec ... and we run off the bvecs

Fix this by properly setting the iov_iter's byte count, plus sending the correct byte count to tcp_sendmsg_locked.

Cc: stable@vger.kernel.org Fixes: c2ff29e99a76 ("siw: Inline do_tcp_sendpages()") Reported-by: kernel test robot oliver.sang@intel.com Closes: https://lore.kernel.org/oe-lkp/202507220801.50a7210-lkp@intel.com Reviewed-by: David Howells dhowells@redhat.com Signed-off-by: Pedro Falcato pfalcato@suse.de

---

v2:

• Add David Howells's Rb on the original patch
• Remove the offset increment, since it's dead code

drivers/infiniband/sw/siw/siw_qp_tx.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/sw/siw/siw_qp_tx.c b/drivers/infiniband/sw/siw/siw_qp_tx.c index 3a08f57d2211..f7dd32c6e5ba 100644 --- a/drivers/infiniband/sw/siw/siw_qp_tx.c +++ b/drivers/infiniband/sw/siw/siw_qp_tx.c @@ -340,18 +340,17 @@ static int siw_tcp_sendpages(struct socket *s, struct page **page, int offset, if (!sendpage_ok(page[i])) msg.msg_flags &= ~MSG_SPLICE_PAGES; bvec_set_page(&bvec, page[i], bytes, offset);

• iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
  

• iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, bytes);
  

  try_page_again: lock_sock(sk);

• rv = tcp_sendmsg_locked(sk, &msg, size);
  

• rv = tcp_sendmsg_locked(sk, &msg, bytes)
  

  release_sock(sk); if (rv > 0) { size -= rv; sent += rv; if (rv != bytes) {

• 		offset += rv;
  	bytes -= rv;
  	goto try_page_again;
  }
  

Acked-by: Bernard Metzler bernard.metzler@linux.dev

Thanks!

Do you want to take the fix through your tree? Otherwise I suspect Vlastimil could simply take it (and possibly resubmit the SLAB PR, which hasn't been merged yet).