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SubjectRe: [merged] exec-open-code-copy_string_kernel.patch removed from -mm tree
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On 2020-06-05 22:19, akpm@linux-foundation.org wrote:
> The patch titled
> Subject: exec: open code copy_string_kernel
> has been removed from the -mm tree. Its filename was
> exec-open-code-copy_string_kernel.patch
>
> This patch was dropped because it was merged into mainline or a subsystem tree
>
> ------------------------------------------------------
> From: Christoph Hellwig <hch@lst.de>
> Subject: exec: open code copy_string_kernel
>
> Currently copy_string_kernel is just a wrapper around copy_strings that
> simplifies the calling conventions and uses set_fs to allow passing a
> kernel pointer. But due to the fact the we only need to handle a single
> kernel argument pointer, the logic can be sigificantly simplified while
> getting rid of the set_fs.
>
> Link: http://lkml.kernel.org/r/20200501104105.2621149-3-hch@lst.de
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> fs/exec.c | 45 +++++++++++++++++++++++++++++++++++----------
> 1 file changed, 35 insertions(+), 10 deletions(-)
>
> --- a/fs/exec.c~exec-open-code-copy_string_kernel
> +++ a/fs/exec.c
> @@ -592,17 +592,42 @@ out:
> */
> int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
> {
> - int r;
> - mm_segment_t oldfs = get_fs();
> - struct user_arg_ptr argv = {
> - .ptr.native = (const char __user *const __user *)&arg,
> - };
> -
> - set_fs(KERNEL_DS);
> - r = copy_strings(1, argv, bprm);
> - set_fs(oldfs);
> + int len = strnlen(arg, MAX_ARG_STRLEN) + 1 /* terminating NUL */;
> + unsigned long pos = bprm->p;
>
> - return r;
> + if (len == 0)
> + return -EFAULT;

Just a quick question, how can len ever be 0 here when len was set to
strnlen() + 1? Should the test be different?

The old version (i.e. copy_strings()) seems to return -EFAULT when
strnlen() returns 0.


Vegard

> + if (!valid_arg_len(bprm, len))
> + return -E2BIG;
> +
> + /* We're going to work our way backwards. */
> + arg += len;
> + bprm->p -= len;
> + if (IS_ENABLED(CONFIG_MMU) && bprm->p < bprm->argmin)
> + return -E2BIG;
> +
> + while (len > 0) {
> + unsigned int bytes_to_copy = min_t(unsigned int, len,
> + min_not_zero(offset_in_page(pos), PAGE_SIZE));
> + struct page *page;
> + char *kaddr;
> +
> + pos -= bytes_to_copy;
> + arg -= bytes_to_copy;
> + len -= bytes_to_copy;
> +
> + page = get_arg_page(bprm, pos, 1);
> + if (!page)
> + return -E2BIG;
> + kaddr = kmap_atomic(page);
> + flush_arg_page(bprm, pos & PAGE_MASK, page);
> + memcpy(kaddr + offset_in_page(pos), arg, bytes_to_copy);
> + flush_kernel_dcache_page(page);
> + kunmap_atomic(kaddr);
> + put_arg_page(page);
> + }
> +
> + return 0;
> }
> EXPORT_SYMBOL(copy_string_kernel);
>

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