On Tue, Jan 22, 2019 at 12:21:52PM +0530, Chandan Rajendra wrote: > On ppc64le, When a string with PAGE_SIZE - 1 (i.e. 64k-1) length is > passed as a "filesystem type" argument to the mount(2) syscall, > copy_mount_string() ends up allocating 64k (the PAGE_SIZE on ppc64le) > worth of space for holding the string in kernel's address space. > > Later, in set_precision() (invoked by get_fs_type() -> > __request_module() -> vsnprintf()), we end up assigning > strlen(fs-type-string) i.e. 65535 as the > value to 'struct printf_spec'->precision member. This field has a width > of 16 bits and it is a signed data type. Hence an invalid value ends > up getting assigned. This causes the "WARN_ONCE(spec->precision != prec, > "precision %d too large", prec)" statement inside set_precision() to be > executed. > > This commit fixes the bug by limiting the length of the string passed by > copy_mount_string() to strndup_user() to PATH_MAX. > > Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxx> > Reported-by: Abdul Haleem <abdhalee@xxxxxxxxxxxxx> > Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Applied
