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;
>
> out_free_interp:
> kfree(elf_interpreter);
> @@ -963,12 +971,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
> goto out_free_dentry;
>
> /* Pass PT_LOPROC..PT_HIPROC headers to arch code */
> - elf_property_phdata = NULL;
> elf_ppnt = interp_elf_phdata;
> for (i = 0; i < interp_elf_ex->e_phnum; i++, elf_ppnt++)
> switch (elf_ppnt->p_type) {
> case PT_GNU_PROPERTY:
> - elf_property_phdata = elf_ppnt;
> + interp_elf_property_phdata = elf_ppnt;
> break;
>
> case PT_LOPROC ... PT_HIPROC:
> @@ -979,10 +986,17 @@ static int load_elf_binary(struct linux_binprm *bprm)
> goto out_free_dentry;
> break;
> }
> +
> + retval = parse_elf_properties(interpreter,
> + interp_elf_property_phdata,
> + true, true, &arch_state);
> + if (retval)
> + goto out_free_dentry;
> +
> }
>
> - retval = parse_elf_properties(interpreter ?: bprm->file,
> - elf_property_phdata, &arch_state);
> + retval = parse_elf_properties(bprm->file, elf_property_phdata,
> + interpreter, false, &arch_state);
> if (retval)
> goto out_free_dentry;
>
> diff --git a/include/linux/elf.h b/include/linux/elf.h
> index c9a46c4e183b..1c45ecf29147 100644
> --- a/include/linux/elf.h
> +++ b/include/linux/elf.h
> @@ -88,13 +88,15 @@ struct arch_elf_state;
> #ifndef CONFIG_ARCH_USE_GNU_PROPERTY
> 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)
> {
> return 0;
> }
> #else
> extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
> - bool compat, struct arch_elf_state *arch);
> + bool compat, bool has_interp, bool is_interp,
> + struct arch_elf_state *arch);
> #endif
>
> #ifdef CONFIG_ARCH_HAVE_ELF_PROT
> --
> 2.30.2
>
--
Kees Cook
