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SubjectRe: [PATCH 8/8] exec: open code copy_string_kernel
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Le 14/04/2020 à 09:01, Christoph Hellwig a écrit :
> 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.


Instead of duplicating almost identical code, can you write a function
that takes whether the source is from user or from kernel, then you just
do things like:

if (from_user)
len = strnlen_user(str, MAX_ARG_STRLEN);
else
len = strnlen(str, MAX_ARG_STRLEN);


if (from_user)
copy_from_user(kaddr+offset, str, bytes_to_copy);
else
memcpy(kaddr+offset, str, bytes_to_copy);

>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/exec.c | 43 ++++++++++++++++++++++++++++++++++---------
> 1 file changed, 34 insertions(+), 9 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index b2a77d5acede..ea90af1fb236 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -592,17 +592,42 @@ static int copy_strings(int argc, struct user_arg_ptr argv,
> */
> 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,
> - };
> + int len = strnlen(arg, MAX_ARG_STRLEN) + 1 /* terminating NUL */;
> + unsigned long pos = bprm->p;
> +
> + if (len == 0)
> + return -EFAULT;
> + 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;
>
> - set_fs(KERNEL_DS);
> - r = copy_strings(1, argv, bprm);
> - set_fs(oldfs);
> + pos -= bytes_to_copy;
> + arg -= bytes_to_copy;
> + len -= bytes_to_copy;
>
> - return r;
> + 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);
>
>

Christophe

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