Messages in this thread | | | Date | Tue, 5 Oct 2021 19:31:09 -0700 | From | Kees Cook <> | Subject | Re: [PATCH] ELF: fix overflow in total mapping size calculation |
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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?
> #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);
> + pt_load = true; > } > } > - if (first_idx == -1) > - return 0; > - > - return cmds[last_idx].p_vaddr + cmds[last_idx].p_memsz - > - ELF_PAGESTART(cmds[first_idx].p_vaddr); > + return pt_load ? (max_addr - min_addr) : 0; > } > > static int elf_read(struct file *file, void *buf, size_t len, loff_t pos)
-Kees
-- Kees Cook
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