Commit 9eb8a659 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds

exec: remove the no longer needed remove_arg_zero()->free_arg_page()

remove_arg_zero() does free_arg_page() for no reason.  This was needed
before and only if CONFIG_MMU=y: see commit 4fc75ff4 ("exec: fix
remove_arg_zero"), install_arg_page() was called for every page != NULL
in bprm->page[] array.  Today install_arg_page() has already gone and
free_arg_page() is nop after another commit b6a2fea3 ("mm: variable
length argument support").

CONFIG_MMU=n does free_arg_pages() in free_bprm() and thus it doesn't
need remove_arg_zero()->free_arg_page() too; apart from get_arg_page()
it never checks if the page in bprm->page[] was allocated or not, so the
"extra" non-freed page is fine.  OTOH, this free_arg_page() can add the
minor pessimization, the caller is going to do copy_strings_kernel()
right after remove_arg_zero() which will likely need to re-allocate the
same page again.

And as Hujunjie pointed out, the "offset == PAGE_SIZE" check is wrong
because we are going to increment bprm->p once again before return, so
CONFIG_MMU=n "leaks" the page anyway if '0' is the final byte in this
page.

NOTE: remove_arg_zero() assumes that argv[0] is null-terminated but this
is not necessarily true.  copy_strings() does "len = strnlen_user(...)",
then copy_from_user(len) but another thread or debuger can overwrite the
trailing '0' in between.  Afaics nothing really bad can happen because
we must always have the null-terminated bprm->filename copied by the 1st
copy_strings_kernel(), but perhaps we should change this code to check
"bprm->p < bprm->exec" anyway, and/or change copy_strings() to ensure
that the last byte in string is always zero.

Link: http://lkml.kernel.org/r/20160517155335.GA31435@redhat.comSigned-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Reported by: hujunjie <jj.net@163.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 725fc629
...@@ -243,10 +243,6 @@ static void put_arg_page(struct page *page) ...@@ -243,10 +243,6 @@ static void put_arg_page(struct page *page)
put_page(page); put_page(page);
} }
static void free_arg_page(struct linux_binprm *bprm, int i)
{
}
static void free_arg_pages(struct linux_binprm *bprm) static void free_arg_pages(struct linux_binprm *bprm)
{ {
} }
...@@ -1499,9 +1495,6 @@ int remove_arg_zero(struct linux_binprm *bprm) ...@@ -1499,9 +1495,6 @@ int remove_arg_zero(struct linux_binprm *bprm)
kunmap_atomic(kaddr); kunmap_atomic(kaddr);
put_arg_page(page); put_arg_page(page);
if (offset == PAGE_SIZE)
free_arg_page(bprm, (bprm->p >> PAGE_SHIFT) - 1);
} while (offset == PAGE_SIZE); } while (offset == PAGE_SIZE);
bprm->p++; bprm->p++;
......
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