On Mon, Jun 01, 2026 at 08:00:12PM +0000, David Hu wrote:

In case MMIO size is bigger than 4G and peer2peer DMA goes through host bridge, we trigger a code path that assigns the total linked IOVA (which is greater than 4G) to mapped_len.

Previously, `mapped_len` was declared as 32-bit `unsigned int`. When accumulating `size_t` lengths, this leads to a silent wrap-around. This truncation causes truncated lengths to be passed to functions like `fill_sg_entry()`.

Fix this by changing `mapped_len` to `size_t` (64-bit). While at it, fix similar potential overflow issues in `calc_sg_nents` by using `size_t` for `nents` and checking against `UINT_MAX` and using `unsigned int` for the loop iterator in `fill_sg_entry` to match.

Fixes: 3aa31a8bb11e ("dma-buf: provide phys_vec to scatter-gather mapping routine") Cc: stable@vger.kernel.org Cc: iommu@lists.linux.dev Reviewed-by: Pranjal Shrivastava praan@google.com Signed-off-by: David Hu xuehaohu@google.com

---

Changes in v5:

• Removed WARN_ON_ONCE from calc_sg_nents() to avoid log noise (Jason).
• Added explicit check for `!nents` in dma_buf_phys_vec_to_sgt() to cleanly return -EINVAL on overflow (Jason).

Changes in v4:

• Added WARN_ON_ONCE() to the nents overflow check to prevent silent failures (Claude Bot).

Changes in v3:

• Removed leftover sentence fragment from the commit message.
• Kept `nents = 0` initialization (previously stated as removed in the v2 changelog) as it is strictly required for the `+=` accumulation loop in `calc_sg_nents()`.

Changes in v2:

• Fixed 'IVOA' -> 'IOVA' typo and expanded commit message (Claude Bot).
• Added Reverse Xmas tree formatting (Pranjal).
• Folded in extra bounds checking for calc_sg_nents() (Pranjal).
• Folded in type consistency fix for fill_sg_entry() (Pranjal).

drivers/dma-buf/dma-buf-mapping.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/dma-buf-mapping.c b/drivers/dma-buf/dma-buf-mapping.c index 794acff2546a..607b7998463d 100644 --- a/drivers/dma-buf/dma-buf-mapping.c +++ b/drivers/dma-buf/dma-buf-mapping.c @@ -10,7 +10,7 @@ static struct scatterlist *fill_sg_entry(struct scatterlist *sgl, size_t length, dma_addr_t addr) { unsigned int len, nents;

• int i;

• unsigned int i;

nents = DIV_ROUND_UP(length, UINT_MAX); for (i = 0; i < nents; i++) { @@ -36,7 +36,7 @@ static unsigned int calc_sg_nents(struct dma_iova_state *state, struct phys_vec *phys_vec, size_t nr_ranges, size_t size) {

• unsigned int nents = 0;

• size_t nents = 0; size_t i;

if (!state || !dma_use_iova(state)) { @@ -51,6 +51,9 @@ static unsigned int calc_sg_nents(struct dma_iova_state *state, nents = DIV_ROUND_UP(size, UINT_MAX); }

• if (nents > UINT_MAX)

I would suggest to use check_add_overflow() while calculating nents instead of this check.

• return 0;
  

• return nents;

} @@ -95,9 +98,10 @@ struct sg_table *dma_buf_phys_vec_to_sgt(struct dma_buf_attachment *attach, size_t nr_ranges, size_t size, enum dma_data_direction dir) {

• unsigned int nents, mapped_len = 0; struct dma_buf_dma *dma; struct scatterlist *sgl;

• size_t mapped_len = 0;
• unsigned int nents; dma_addr_t addr; size_t i; int ret;

@@ -133,6 +137,11 @@ struct sg_table *dma_buf_phys_vec_to_sgt(struct dma_buf_attachment *attach, } nents = calc_sg_nents(dma->state, phys_vec, nr_ranges, size);

• if (!nents) {

• ret = -EINVAL;
  

• goto err_free_state;
  

• }

Technically, this hunk is not necessary, since sg_alloc_table() will return -EINVAL when nents == 0. At least, that is the behavior I relied on.

Thanks

• ret = sg_alloc_table(&dma->sgt, nents, GFP_KERNEL | __GFP_ZERO); if (ret) goto err_free_state;

-- 2.54.0.929.g9b7fa37559-goog