4.14-stable review patch. If anyone has any objections, please let me know.
------------------ From: Jeff Moyer <[email protected]> commit 957ac8c421ad8b5eef9b17fe98e146d8311a541e upstream. PMD faults on a zero length file on a file system mounted with -o dax will not generate SIGBUS as expected. fd = open(...O_TRUNC); addr = mmap(NULL, 2*1024*1024, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); *addr = 'a'; <expect SIGBUS> The problem is this code in dax_iomap_pmd_fault: max_pgoff = (i_size_read(inode) - 1) >> PAGE_SHIFT; If the inode size is zero, we end up with a max_pgoff that is way larger than 0. :) Fix it by using DIV_ROUND_UP, as is done elsewhere in the kernel. I tested this with some simple test code that ensured that SIGBUS was received where expected. Fixes: 642261ac995e ("dax: add struct iomap based DAX PMD support") Signed-off-by: Jeff Moyer <[email protected]> Signed-off-by: Dan Williams <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- fs/dax.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/fs/dax.c +++ b/fs/dax.c @@ -1327,7 +1327,7 @@ static int dax_iomap_pmd_fault(struct vm * this is a reliable test. */ pgoff = linear_page_index(vma, pmd_addr); - max_pgoff = (i_size_read(inode) - 1) >> PAGE_SHIFT; + max_pgoff = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); trace_dax_pmd_fault(inode, vmf, max_pgoff, 0); @@ -1351,13 +1351,13 @@ static int dax_iomap_pmd_fault(struct vm if ((pmd_addr + PMD_SIZE) > vma->vm_end) goto fallback; - if (pgoff > max_pgoff) { + if (pgoff >= max_pgoff) { result = VM_FAULT_SIGBUS; goto out; } /* If the PMD would extend beyond the file size */ - if ((pgoff | PG_PMD_COLOUR) > max_pgoff) + if ((pgoff | PG_PMD_COLOUR) >= max_pgoff) goto fallback; /*
