diff options
| author | Kees Cook <keescook@chromium.org> | 2017-06-23 15:08:57 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-06-29 12:48:50 +0200 |
| commit | 1d3d0f8b7cf758136ed36b30620442d989601737 (patch) | |
| tree | 0b812c7d3390e1622f7b356c5847731d7ca5f8a8 | |
| parent | 22da7ca81a3aad1af021c770b578acad86d63681 (diff) | |
fs/exec.c: account for argv/envp pointers
commit 98da7d08850fb8bdeb395d6368ed15753304aa0c upstream.
When limiting the argv/envp strings during exec to 1/4 of the stack limit,
the storage of the pointers to the strings was not included. This means
that an exec with huge numbers of tiny strings could eat 1/4 of the stack
limit in strings and then additional space would be later used by the
pointers to the strings.
For example, on 32-bit with a 8MB stack rlimit, an exec with 1677721
single-byte strings would consume less than 2MB of stack, the max (8MB /
4) amount allowed, but the pointers to the strings would consume the
remaining additional stack space (1677721 * 4 == 6710884).
The result (1677721 + 6710884 == 8388605) would exhaust stack space
entirely. Controlling this stack exhaustion could result in
pathological behavior in setuid binaries (CVE-2017-1000365).
[akpm@linux-foundation.org: additional commenting from Kees]
Fixes: b6a2fea39318 ("mm: variable length argument support")
Link: http://lkml.kernel.org/r/20170622001720.GA32173@beast
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | fs/exec.c | 28 |
1 files changed, 24 insertions, 4 deletions
diff --git a/fs/exec.c b/fs/exec.c index 3a6de10d3891..02153068a694 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -206,8 +206,26 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, if (write) { unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start; + unsigned long ptr_size; struct rlimit *rlim; + /* + * 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); /* @@ -225,13 +243,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, * to work from. */ rlim = current->signal->rlim; - if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) { - put_page(page); - return NULL; - } + if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) + goto fail; } return page; + +fail: + put_page(page); + return NULL; } static void put_arg_page(struct page *page) |