On Thu, Nov 19, 2015 at 05:03:15PM -0800, Kees Cook wrote: > On Thu, Nov 19, 2015 at 5:00 PM, Willy Tarreau <w@xxxxxx> wrote: > > Hi Kees, > > > > On Thu, Nov 19, 2015 at 04:10:43PM -0800, Kees Cook wrote: > >> Normally, when a user can modify a file that has setuid or setgid bits, > >> those bits are cleared when they are not the file owner or a member of the > >> group. This is enforced when using write() directly but not when writing > >> to a shared mmap on the file. This could allow the file writer to gain > >> privileges by changing the binary without losing the setuid/setgid bits. > >> > >> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > >> Cc: stable@xxxxxxxxxxxxxxx > >> --- > >> mm/memory.c | 1 + > >> 1 file changed, 1 insertion(+) > >> > >> diff --git a/mm/memory.c b/mm/memory.c > >> index deb679c31f2a..4c970a4e0057 100644 > >> --- a/mm/memory.c > >> +++ b/mm/memory.c > >> @@ -2036,6 +2036,7 @@ static inline int wp_page_reuse(struct mm_struct *mm, > >> > >> if (!page_mkwrite) > >> file_update_time(vma->vm_file); > >> + file_remove_privs(vma->vm_file); > > > > I thought you said in one of the early mails of this thread that it > > didn't work. Or maybe I misunderstood. > > I had a think-o in my earlier attempts. I understood the meaning of > page_mkwrite incorrectly. > > > Also, don't you think we should move that into the if (!page_mkwrite) > > just like for the time update ? > > Nope, page_mkwrite indicates if there was a vmops call to > page_mkwrite. In this case, it means "I will update the file time if > the filesystem driver didn't take care of it like it should". For > file_remove_privs, we want to always do it, since we should not depend > on filesystems to do it. Ah OK, thanks for the explanation, I didn't understand it like this at all last time I read it. Cheers, Willy -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>