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author | Oleg Nesterov <oleg@redhat.com> | 2016-05-23 16:24:08 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-05-23 17:04:14 -0700 |
commit | 9eb8a659dea694b0dcbd6287f6b1fbdc523b80bc (patch) | |
tree | 35ad406db615fa0a81a181df966c1229585083da /fs/exec.c | |
parent | 725fc629ff2545b061407305ae51016c9f928fce (diff) | |
download | linux-stable-9eb8a659dea694b0dcbd6287f6b1fbdc523b80bc.tar.gz linux-stable-9eb8a659dea694b0dcbd6287f6b1fbdc523b80bc.tar.bz2 linux-stable-9eb8a659dea694b0dcbd6287f6b1fbdc523b80bc.zip |
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 4fc75ff4816c ("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 b6a2fea39318 ("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.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported by: hujunjie <jj.net@163.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/exec.c')
-rw-r--r-- | fs/exec.c | 7 |
1 files changed, 0 insertions, 7 deletions
diff --git a/fs/exec.c b/fs/exec.c index e92419fd78b3..4f079bd083af 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -243,10 +243,6 @@ static void put_arg_page(struct 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) { } @@ -1499,9 +1495,6 @@ int remove_arg_zero(struct linux_binprm *bprm) 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++; |