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exec: separate MM_ANONPAGES and RLIMIT_STACK accounting

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get_arg_page() checks bprm->rlim_stack.rlim_cur and re-calculates the
"extra" size for argv/envp pointers every time, this is a bit ugly and
even not strictly correct: acct_arg_size() must not account this size.

Remove all the rlimit code in get_arg_page().  Instead, add bprm->argmin
calculated once at the start of __do_execve_file() and change
copy_strings to check bprm->p >= bprm->argmin.

The patch adds the new helper, prepare_arg_pages() which initializes
bprm->argc/envc and bprm->argmin.

[oleg@redhat.com: fix !CONFIG_MMU version of get_arg_page()]
  Link: http://lkml.kernel.org/r/20181126122307.GA1660@redhat.com
[akpm@linux-foundation.org: use max_t]
Link: http://lkml.kernel.org/r/20181112160910.GA28440@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2019-01-03 15:28:11 -08:00 committed by Linus Torvalds
parent 8099b047ec
commit 655c16a8ce
2 changed files with 53 additions and 53 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

105
fs/exec.c
View file

@ -218,55 +218,10 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
if (ret <= 0)
return NULL;
if (write) {
unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
unsigned long ptr_size, limit;
/*
* Since the stack will hold pointers to the strings, we
* must account for them as well.
*
* The size calculation is the entire vma while each arg page is
* built, so each time we get here it's calculating how far it
* is currently (rather than each call being just the newly
* added size from the arg page). As a result, we need to
* always add the entire size of the pointers, so that on the
* last call to get_arg_page() we'll actually have the entire
* correct size.
*/
ptr_size = (bprm->argc + bprm->envc) * sizeof(void *);
if (ptr_size > ULONG_MAX - size)
goto fail;
size += ptr_size;
acct_arg_size(bprm, size / PAGE_SIZE);
/*
* We've historically supported up to 32 pages (ARG_MAX)
* of argument strings even with small stacks
*/
if (size <= ARG_MAX)
return page;
/*
* Limit to 1/4 of the max stack size or 3/4 of _STK_LIM
* (whichever is smaller) for the argv+env strings.
* This ensures that:
* - the remaining binfmt code will not run out of stack space,
* - the program will have a reasonable amount of stack left
* to work from.
*/
limit = _STK_LIM / 4 * 3;
limit = min(limit, bprm->rlim_stack.rlim_cur / 4);
if (size > limit)
goto fail;
}
if (write)
acct_arg_size(bprm, vma_pages(bprm->vma));
return page;
fail:
put_page(page);
return NULL;
}
static void put_arg_page(struct page *page)
@ -492,6 +447,50 @@ static int count(struct user_arg_ptr argv, int max)
return i;
}
static int prepare_arg_pages(struct linux_binprm *bprm,
struct user_arg_ptr argv, struct user_arg_ptr envp)
{
unsigned long limit, ptr_size;
bprm->argc = count(argv, MAX_ARG_STRINGS);
if (bprm->argc < 0)
return bprm->argc;
bprm->envc = count(envp, MAX_ARG_STRINGS);
if (bprm->envc < 0)
return bprm->envc;
/*
* Limit to 1/4 of the max stack size or 3/4 of _STK_LIM
* (whichever is smaller) for the argv+env strings.
* This ensures that:
* - the remaining binfmt code will not run out of stack space,
* - the program will have a reasonable amount of stack left
* to work from.
*/
limit = _STK_LIM / 4 * 3;
limit = min(limit, bprm->rlim_stack.rlim_cur / 4);
/*
* We've historically supported up to 32 pages (ARG_MAX)
* of argument strings even with small stacks
*/
limit = max_t(unsigned long, limit, ARG_MAX);
/*
* We must account for the size of all the argv and envp pointers to
* the argv and envp strings, since they will also take up space in
* the stack. They aren't stored until much later when we can't
* signal to the parent that the child has run out of stack space.
* Instead, calculate it here so it's possible to fail gracefully.
*/
ptr_size = (bprm->argc + bprm->envc) * sizeof(void *);
if (limit <= ptr_size)
return -E2BIG;
limit -= ptr_size;
bprm->argmin = bprm->p - limit;
return 0;
}
/*
* 'copy_strings()' copies argument/environment strings from the old
* processes's memory to the new process's stack. The call to get_user_pages()
@ -527,6 +526,10 @@ static int copy_strings(int argc, struct user_arg_ptr argv,
pos = bprm->p;
str += len;
bprm->p -= len;
#ifdef CONFIG_MMU
if (bprm->p < bprm->argmin)
goto out;
#endif
while (len > 0) {
int offset, bytes_to_copy;
@ -1789,12 +1792,8 @@ static int __do_execve_file(int fd, struct filename *filename,
if (retval)
goto out_unmark;
bprm->argc = count(argv, MAX_ARG_STRINGS);
if ((retval = bprm->argc) < 0)
goto out;
bprm->envc = count(envp, MAX_ARG_STRINGS);
if ((retval = bprm->envc) < 0)
retval = prepare_arg_pages(bprm, argv, envp);
if (retval < 0)
goto out;
retval = prepare_binprm(bprm);

1
include/linux/binfmts.h
View file

@ -25,6 +25,7 @@ struct linux_binprm {
#endif
struct mm_struct *mm;
unsigned long p; /* current top of mem */
unsigned long argmin; /* rlimit marker for copy_strings() */
unsigned int
/*
* True after the bprm_set_creds hook has been called once