Subject: [PATCH net v2] net: devmem: reject dma-buf bind with non-page-aligned size or SG length

From: David Carlier <[email-masked]>
Date: Tue, 19 May 2026 21:35:30 +0100

net_devmem_bind_dmabuf() trusts dmabuf->size and sg_dma_len() to be
PAGE_SIZE multiples without checking:

  - tx_vec is sized dmabuf->size / PAGE_SIZE, and
    net_devmem_get_niov_at() only bounds-checks virt_addr < dmabuf->size
    before indexing tx_vec[virt_addr / PAGE_SIZE]. With size =
    N*PAGE_SIZE + r (1 <= r < PAGE_SIZE), sendmsg() at iov_base =
    N*PAGE_SIZE passes the bound check and reads tx_vec[N] -- one past.

  - owner->area.num_niovs = len / PAGE_SIZE while gen_pool_add_owner()
    covers the full byte len, so a non-page-multiple non-final sg
    desyncs num_niovs from the gen_pool region for every later sg, on
    both RX and TX.

dma-buf does not require page-aligned sizes, so the bind path has to
enforce what its own indexing assumes. Reject both with -EINVAL.

The size check is TX-only (only tx_vec is sized off dmabuf->size); the
SG-length check covers both directions.

Fixes: bd61848900bf ("net: devmem: Implement TX path")
Cc: [email-masked]
Signed-off-by: David Carlier <[email-masked]>
---
Changes in v2:
  - Reframe commit message around the kernel-side OOB instead of
    "real exporters already page-align", which read as the OOB being
    unreachable and undercut Cc: stable (Stanislav Fomichev).
  - Hoist the SG-length check out of the if (TX) branch so it covers
    RX too; RX has the same num_niovs / gen_pool desync on a
    contract-violating exporter, just without an OOB. Keep the
    size-multiple check TX-only (Stanislav Fomichev).
  - Drop bool todevice; compare direction == DMA_TO_DEVICE inline to
    match the existing call site at the tx_vec[] assignment
    (Bobby Eshleman).

 net/core/devmem.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/net/core/devmem.c b/net/core/devmem.c
index 468344739db2..4f71de44c0fb 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -241,6 +241,11 @@ net_devmem_bind_dmabuf(struct net_device *dev,
 	}
 
 	if (direction == DMA_TO_DEVICE) {
+		if (!IS_ALIGNED(dmabuf->size, PAGE_SIZE)) {
+			err = -EINVAL;
+			NL_SET_ERR_MSG(extack, "TX dma-buf size must be a multiple of PAGE_SIZE");
+			goto err_unmap;
+		}
 		binding->tx_vec = kvmalloc_objs(struct net_iov *,
 						dmabuf->size / PAGE_SIZE);
 		if (!binding->tx_vec) {
@@ -267,6 +272,12 @@ net_devmem_bind_dmabuf(struct net_device *dev,
 		size_t len = sg_dma_len(sg);
 		struct net_iov *niov;
 
+		if (!IS_ALIGNED(len, PAGE_SIZE)) {
+			err = -EINVAL;
+			NL_SET_ERR_MSG(extack, "dma-buf SG length must be PAGE_SIZE aligned");
+			goto err_free_chunks;
+		}
+
 		owner = kzalloc_node(sizeof(*owner), GFP_KERNEL,
 				     dev_to_node(&dev->dev));
 		if (!owner) {
-- 
2.53.0