Messages in this thread Patch in this message | | | Subject | Re: [PATCH 8/8] exec: open code copy_string_kernel | From | Christophe Leroy <> | Date | Sat, 18 Apr 2020 10:15:42 +0200 |
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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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