On Mon, Mar 07, 2022 at 04:00:15PM -0800, Kees Cook wrote:
> On Mon, Feb 28, 2022 at 01:06:05PM +0000, Mark Brown wrote:
> > Currently the ELF code only attempts to parse properties on the image
> > that will start execution, either the interpreter or for statically linked
> > executables the main executable. The expectation is that any property
> > handling for the main executable will be done by the interpreter. This is
> > a bit inconsistent since we do map the executable and is causing problems
> > for the arm64 BTI support when used in conjunction with systemd's use of
> > seccomp to implement MemoryDenyWriteExecute which stops the dynamic linker
> > adjusting the permissions of executable segments.
> >
> > Allow architectures to handle properties for both the dynamic linker and
> > main executable, adjusting arch_parse_elf_properties() to have a new
> > flag is_interp flag as with arch_elf_adjust_prot() and calling it for
> > both the main executable and any intepreter.
> >
> > The user of this code, arm64, is adapted to ensure that there is no
> > functional change.
> >
> > Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
> > Tested-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> > Reviewed-by: Dave Martin <Dave.Martin@xxxxxxx>
> > Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> > ---
> > arch/arm64/include/asm/elf.h | 3 ++-
> > fs/binfmt_elf.c | 32 +++++++++++++++++++++++---------
> > include/linux/elf.h | 4 +++-
> > 3 files changed, 28 insertions(+), 11 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> > index 97932fbf973d..5cc002376abe 100644
> > --- a/arch/arm64/include/asm/elf.h
> > +++ b/arch/arm64/include/asm/elf.h
> > @@ -259,6 +259,7 @@ struct arch_elf_state {
> >
> > static inline int arch_parse_elf_property(u32 type, const void *data,
> > size_t datasz, bool compat,
> > + bool has_interp, bool is_interp,
> > struct arch_elf_state *arch)
>
> Adding more and more args to a functions like this gives me the sense
> that some kind of argument structure is needed.
>
> Once I get enough unit testing written in here, I'm hoping to refactor
> a bunch of this. To the future! :)
>
> > @@ -828,6 +832,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> > unsigned long error;
> > struct elf_phdr *elf_ppnt, *elf_phdata, *interp_elf_phdata = NULL;
> > struct elf_phdr *elf_property_phdata = NULL;
> > + struct elf_phdr *interp_elf_property_phdata = NULL;
> > unsigned long elf_bss, elf_brk;
> > int bss_prot = 0;
> > int retval, i;
> > @@ -865,6 +870,9 @@ static int load_elf_binary(struct linux_binprm *bprm)
> > for (i = 0; i < elf_ex->e_phnum; i++, elf_ppnt++) {
> > char *elf_interpreter;
> >
> > + if (interpreter && elf_property_phdata)
> > + break;
> > +
>
> This is not okay. This introduces a memory resource leak for malicious
> ELF files with multiple INTERP headers.
>
> > if (elf_ppnt->p_type == PT_GNU_PROPERTY) {
> > elf_property_phdata = elf_ppnt;
> > continue;
> > @@ -919,7 +927,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> > if (retval < 0)
> > goto out_free_dentry;
> >
> > - break;
> > + continue;
>
> Because of this.
>
> As a fix, I'd expect the PT_INTERP test to be updated:
>
> if (interpreter || elf_ppnt->p_type != PT_INTERP)
> continue;
Thanks, Kees. I'll drop this branch from -next until it's been resolved.
Will
