This is a breaking change for SELinux users that restrict EXECMEM: It might break gdb if gdb is executed in a domain that does not have EXECMEM privilege over the debuggee domain.
Unlike most other SELinux hooks, this one takes the subject credentials as an argument instead of looking up current_cred(). This is done because the security_forced_write() LSM hook can be invoked from within the write handler of /proc/$pid/mem, where current_cred() is pretty useless. Signed-off-by: Jann Horn <[email protected]> Reviewed-by: Janis Danisevskis <[email protected]> --- security/selinux/hooks.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 13185a6..e36682a 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2149,6 +2149,20 @@ static int selinux_ptrace_traceme(struct task_struct *parent) return task_has_perm(parent, current, PROCESS__PTRACE); } +static int selinux_forced_write(struct vm_area_struct *vma, + const struct cred *subject_cred, + const struct cred *object_cred) +{ + /* Permitting a write to readonly memory is fine - making the readonly + * memory executable afterwards would require EXECMOD permission because + * anon_vma would be non-NULL. + */ + if ((vma->vm_flags & VM_EXEC) == 0) + return 0; + + return cred_has_perm(subject_cred, object_cred, PROCESS__EXECMEM); +} + static int selinux_capget(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted) { @@ -6033,6 +6047,7 @@ static struct security_hook_list selinux_hooks[] = { LSM_HOOK_INIT(ptrace_access_check, selinux_ptrace_access_check), LSM_HOOK_INIT(ptrace_traceme, selinux_ptrace_traceme), + LSM_HOOK_INIT(forced_write, selinux_forced_write), LSM_HOOK_INIT(capget, selinux_capget), LSM_HOOK_INIT(capset, selinux_capset), LSM_HOOK_INIT(capable, selinux_capable), -- 2.1.4
