Messages in this thread | | | Date | Thu, 7 Oct 2021 10:40:01 -0700 | From | Kees Cook <> | Subject | Re: [PATCH] ELF: fix overflow in total mapping size calculation |
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On Thu, Oct 07, 2021 at 08:20:03PM +0300, Alexey Dobriyan wrote: > On Tue, Oct 05, 2021 at 07:31:09PM -0700, Kees Cook wrote: > > On Sun, Oct 03, 2021 at 03:11:24PM +0300, Alexey Dobriyan wrote: > > > Kernel assumes that ELF program headers are ordered by mapping address, > > > but doesn't enforce it. It is possible to make mapping size extremely huge > > > by simply shuffling first and last PT_LOAD segments. > > > > > > As long as PT_LOAD segments do not overlap, it is silly to require > > > sorting by v_addr anyway because mmap() doesn't care. > > > > > > Don't assume PT_LOAD segments are sorted and calculate min and max > > > addresses correctly. > > > > Nice! Yes, this all make sense. > > > > > > > > Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> > > > --- > > > > > > fs/binfmt_elf.c | 23 +++++++++++------------ > > > 1 file changed, 11 insertions(+), 12 deletions(-) > > > > > > --- a/fs/binfmt_elf.c > > > +++ b/fs/binfmt_elf.c > > > @@ -93,7 +93,7 @@ static int elf_core_dump(struct coredump_params *cprm); > > > #define ELF_CORE_EFLAGS 0 > > > #endif > > > > > > -#define ELF_PAGESTART(_v) ((_v) & ~(unsigned long)(ELF_MIN_ALIGN-1)) > > > +#define ELF_PAGESTART(_v) ((_v) & ~(int)(ELF_MIN_ALIGN-1)) > > > > Errr, this I don't like. I assume this is because of the min() use > > below? > > Yes, this is to shut up the warning. > > The macro is slightly incorrect because "_v" can be either uint32_t or > uint64_t. But standard ALIGN macros are slightly incorrect too.
Right, but "int" is neither 64-sized nor unsigned. :P I would just leave this macro as-is.
> > I don't want to clean this particular mess right now. Those are separate stables. > > > > #define ELF_PAGEOFFSET(_v) ((_v) & (ELF_MIN_ALIGN-1)) > > > #define ELF_PAGEALIGN(_v) (((_v) + ELF_MIN_ALIGN - 1) & ~(ELF_MIN_ALIGN - 1)) > > > > > > @@ -399,22 +399,21 @@ static unsigned long elf_map(struct file *filep, unsigned long addr, > > > return(map_addr); > > > } > > > > > > -static unsigned long total_mapping_size(const struct elf_phdr *cmds, int nr) > > > +static unsigned long total_mapping_size(const struct elf_phdr *phdr, int nr) > > > { > > > - int i, first_idx = -1, last_idx = -1; > > > + elf_addr_t min_addr = -1; > > > + elf_addr_t max_addr = 0; > > > + bool pt_load = false; > > > + int i; > > > > > > for (i = 0; i < nr; i++) { > > > - if (cmds[i].p_type == PT_LOAD) { > > > - last_idx = i; > > > - if (first_idx == -1) > > > - first_idx = i; > > > + if (phdr[i].p_type == PT_LOAD) { > > > + min_addr = min(min_addr, ELF_PAGESTART(phdr[i].p_vaddr)); > > > + max_addr = max(max_addr, phdr[i].p_vaddr + phdr[i].p_memsz); > > > > How about: > > min_addr = min_t(elf_addr_t, min_addr, ELF_PAGESTART(phdr[i].p_vaddr)); > > max_addr = max_t(elf_addr_t, max_addr, phdr[i].p_vaddr + phdr[i].p_memsz); > > No! The proper fix is to fix ELF_PAGESTART().
Why? The warning from min() is about making sure there isn't an unexpected type conversion. min_t() uses an explicit type, so why not the above?
-- Kees Cook
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