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: [email protected]
> Cc: [email protected]
> Reviewed-by: Pranjal Shrivastava <[email protected]>
> Signed-off-by: David Hu <[email protected]>
> ---
> 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
>
