The patch titled
Subject: exec: remove the no longer needed remove_arg_zero()->free_arg_page()
has been added to the -mm tree. Its filename is
exec-remove-the-no-longer-needed-remove_arg_zero-free_arg_page.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/exec-remove-the-no-longer-needed-remove_arg_zero-free_arg_page.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/exec-remove-the-no-longer-needed-remove_arg_zero-free_arg_page.patch
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------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: 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 the 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 b6a2fea39 ("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@xxxxxxxxxx
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Reported by: hujunjie <jj.net@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/exec.c | 7 -------
1 file changed, 7 deletions(-)
diff -puN fs/exec.c~exec-remove-the-no-longer-needed-remove_arg_zero-free_arg_page fs/exec.c
--- a/fs/exec.c~exec-remove-the-no-longer-needed-remove_arg_zero-free_arg_page
+++ a/fs/exec.c
@@ -243,10 +243,6 @@ static void put_arg_page(struct page *pa
put_page(page);
}
-static void free_arg_page(struct linux_binprm *bprm, int i)
-{
-}
-
static void free_arg_pages(struct linux_binprm *bprm)
{
}
@@ -1481,9 +1477,6 @@ int remove_arg_zero(struct linux_binprm
kunmap_atomic(kaddr);
put_arg_page(page);
-
- if (offset == PAGE_SIZE)
- free_arg_page(bprm, (bprm->p >> PAGE_SHIFT) - 1);
} while (offset == PAGE_SIZE);
bprm->p++;
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
userfaultfd-dont-pin-the-user-memory-in-userfaultfd_file_create.patch
wait-ptrace-assume-__wall-if-the-child-is-traced.patch
wait-allow-sys_waitid-to-accept-__wnothread-__wclone-__wall.patch
signal-move-the-sig-sigrtmin-check-into-siginmasksig.patch
exec-remove-the-no-longer-needed-remove_arg_zero-free_arg_page.patch
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