From: Oleg Nesterov <oleg@xxxxxxxxxx> Subject: exec: separate MM_ANONPAGES and RLIMIT_STACK accounting 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@xxxxxxxxxx: fix !CONFIG_MMU version of get_arg_page()] Link: http://lkml.kernel.org/r/20181126122307.GA1660@xxxxxxxxxx [akpm@xxxxxxxxxxxxxxxxxxxx: use max_t] Link: http://lkml.kernel.org/r/20181112160910.GA28440@xxxxxxxxxx Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/exec.c | 105 ++++++++++++++++++-------------------- include/linux/binfmts.h | 1 2 files changed, 53 insertions(+), 53 deletions(-) --- a/fs/exec.c~exec-separate-mm_anonpages-and-rlimit_stack-accounting +++ a/fs/exec.c @@ -218,55 +218,10 @@ static struct page *get_arg_page(struct 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 arg 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 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, stru 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); --- a/include/linux/binfmts.h~exec-separate-mm_anonpages-and-rlimit_stack-accounting +++ a/include/linux/binfmts.h @@ -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 _
