Creation of a new LSM hook to check if a given configuration of vmflags, for a new memory allocation request, should be allowed or not. It's placed in "do_mmap", "do_brk_flags", "__install_special_mapping" and "setup_arg_pages". When loading an ELF, this hook is also used to determine what to do with an RWE PT_GNU_STACK header. This allows LSM to force the loader to silently ignore executable stack markings, which is useful a thing to do when trampoline emulation is available.
Signed-off-by: Salvatore Mesoraca <[email protected]> --- fs/binfmt_elf.c | 3 ++- fs/binfmt_elf_fdpic.c | 3 ++- fs/exec.c | 4 ++++ include/linux/lsm_hooks.h | 7 +++++++ include/linux/security.h | 6 ++++++ mm/mmap.c | 13 +++++++++++++ security/security.c | 5 +++++ 7 files changed, 39 insertions(+), 2 deletions(-) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 83732fe..a935087 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -803,7 +803,8 @@ static int load_elf_binary(struct linux_binprm *bprm) for (i = 0; i < loc->elf_ex.e_phnum; i++, elf_ppnt++) switch (elf_ppnt->p_type) { case PT_GNU_STACK: - if (elf_ppnt->p_flags & PF_X) + if (elf_ppnt->p_flags & PF_X && + !security_check_vmflags(VM_EXEC|VM_READ|VM_WRITE)) executable_stack = EXSTACK_ENABLE_X; else executable_stack = EXSTACK_DISABLE_X; diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c index 429326b..647dfae 100644 --- a/fs/binfmt_elf_fdpic.c +++ b/fs/binfmt_elf_fdpic.c @@ -167,7 +167,8 @@ static int elf_fdpic_fetch_phdrs(struct elf_fdpic_params *params, if (phdr->p_type != PT_GNU_STACK) continue; - if (phdr->p_flags & PF_X) + if (phdr->p_flags & PF_X && + !security_check_vmflags(VM_EXEC|VM_READ|VM_WRITE)) params->flags |= ELF_FDPIC_FLAG_EXEC_STACK; else params->flags |= ELF_FDPIC_FLAG_NOEXEC_STACK; diff --git a/fs/exec.c b/fs/exec.c index 1d6243d..ba5a4da 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -748,6 +748,10 @@ int setup_arg_pages(struct linux_binprm *bprm, vm_flags |= mm->def_flags; vm_flags |= VM_STACK_INCOMPLETE_SETUP; + ret = security_check_vmflags(vm_flags); + if (ret) + goto out_unlock; + ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end, vm_flags); if (ret) diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index 8298e75..8d7ccbd 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -484,6 +484,11 @@ * @reqprot contains the protection requested by the application. * @prot contains the protection that will be applied by the kernel. * Return 0 if permission is granted. + * @check_vmflags: + * Check if the requested @vmflags are allowed. + * @vmflags contains the requested vmflags. + * Return 0 if the operation is allowed to continue otherwise return + * the appropriate error code. * @file_lock: * Check permission before performing file locking operations. * Note: this hook mediates both flock and fcntl style locks. @@ -1525,6 +1530,7 @@ unsigned long prot, unsigned long flags); int (*file_mprotect)(struct vm_area_struct *vma, unsigned long reqprot, unsigned long prot); + int (*check_vmflags)(vm_flags_t vmflags); int (*file_lock)(struct file *file, unsigned int cmd); int (*file_fcntl)(struct file *file, unsigned int cmd, unsigned long arg); @@ -1812,6 +1818,7 @@ struct security_hook_heads { struct list_head mmap_addr; struct list_head mmap_file; struct list_head file_mprotect; + struct list_head check_vmflags; struct list_head file_lock; struct list_head file_fcntl; struct list_head file_set_fowner; diff --git a/include/linux/security.h b/include/linux/security.h index 73f1ef6..ac16262 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -311,6 +311,7 @@ int security_mmap_file(struct file *file, unsigned long prot, int security_mmap_addr(unsigned long addr); int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot, unsigned long prot); +int security_check_vmflags(vm_flags_t vmflags); int security_file_lock(struct file *file, unsigned int cmd); int security_file_fcntl(struct file *file, unsigned int cmd, unsigned long arg); void security_file_set_fowner(struct file *file); @@ -845,6 +846,11 @@ static inline int security_file_mprotect(struct vm_area_struct *vma, return 0; } +static inline int security_check_vmflags(vm_flags_t vmflags) +{ + return 0; +} + static inline int security_file_lock(struct file *file, unsigned int cmd) { return 0; diff --git a/mm/mmap.c b/mm/mmap.c index 924839f..88d6953 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1326,6 +1326,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr, { struct mm_struct *mm = current->mm; int pkey = 0; + int error; *populate = 0; @@ -1378,6 +1379,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr, vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) | mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC; + error = security_check_vmflags(vm_flags); + if (error) + return error; + if (flags & MAP_LOCKED) if (!can_do_mlock()) return -EPERM; @@ -2888,6 +2893,10 @@ static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long return -EINVAL; flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags; + error = security_check_vmflags(flags); + if (error) + return error; + error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED); if (offset_in_page(error)) return error; @@ -3284,6 +3293,10 @@ static struct vm_area_struct *__install_special_mapping( int ret; struct vm_area_struct *vma; + ret = security_check_vmflags(vm_flags); + if (ret) + return ERR_PTR(ret); + vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL); if (unlikely(vma == NULL)) return ERR_PTR(-ENOMEM); diff --git a/security/security.c b/security/security.c index b0562b6..0df8988 100644 --- a/security/security.c +++ b/security/security.c @@ -939,6 +939,11 @@ int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot, return call_int_hook(file_mprotect, 0, vma, reqprot, prot); } +int security_check_vmflags(vm_flags_t vmflags) +{ + return call_int_hook(check_vmflags, 0, vmflags); +} + int security_file_lock(struct file *file, unsigned int cmd) { return call_int_hook(file_lock, 0, file, cmd); -- 1.9.1
