re: fsdax: output address in dax_iomap_pfn() and rename it

[Colin King (gmail)]

Hi,

Static analysis with clang scan-build found a potential issue with the 
following commit in linux-next today:

commit 1447ac26a96463a05ad9f5cfba7eef43d52913ef
Author: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
Date:   Fri Jun 3 13:37:32 2022 +0800

    fsdax: output address in dax_iomap_pfn() and rename it


The analysis is as follows:


static int dax_iomap_direct_access(const struct iomap *iomap, loff_t pos,
                size_t size, void **kaddr, pfn_t *pfnp)
{
        pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
        int id, rc;
        long length;

        id = dax_read_lock();
        length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
                                   DAX_ACCESS, kaddr, pfnp);
        if (length < 0) {
                rc = length;
                goto out;
        }
        if (!pfnp)
                goto out_check_addr;

The above check jumps to out_check_addr, if kaddr is null then rc is not 
set and a garbage uninitialized value for rc is returned on the out path.


        rc = -EINVAL;
        if (PFN_PHYS(length) < size)
                goto out;
        if (pfn_t_to_pfn(*pfnp) & (PHYS_PFN(size)-1))
                goto out;
        /* For larger pages we need devmap */
        if (length > 1 && !pfn_t_devmap(*pfnp))
                goto out;
        rc = 0;

out_check_addr:
        if (!kaddr)
                goto out;
        if (!*kaddr)
                rc = -EFAULT;
out:
        dax_read_unlock(id);
        return rc;
}


Colin