@@ -1259,6 +1259,12 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
perf_event_comm(tsk, exec);
}
+/*
+ * Calling this is the point of no return. None of the failures will be
+ * seen by userspace since either the process is already taking a fatal
+ * signal (via de_thread() or coredump), or will have SEGV raised
+ * (after exec_mmap()) by search_binary_handlers (see below).
+ */
int flush_old_exec(struct linux_binprm * bprm)
{
int retval;
@@ -1286,7 +1292,13 @@ int flush_old_exec(struct linux_binprm * bprm)
if (retval)
goto out;
- bprm->mm = NULL; /* We're using it now */
+ /*
+ * After clearing bprm->mm (to mark that current is using the
+ * prepared mm now), we have nothing left of the original
+ * process. If anything from here on returns an error, the check
+ * in search_binary_handler() will SEGV current.
+ */
+ bprm->mm = NULL;
set_fs(USER_DS);
current->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
@@ -1333,7 +1345,6 @@ void setup_new_exec(struct linux_binprm * bprm)
{
arch_pick_mmap_layout(current->mm);
- /* This is the point of no return */
current->sas_ss_sp = current->sas_ss_size = 0;
if (uid_eq(current_euid(), current_uid()) && gid_eq(current_egid(), current_gid()))
@@ -1351,7 +1362,6 @@ void setup_new_exec(struct linux_binprm * bprm)
*/
current->mm->task_size = TASK_SIZE;
- /* install the new credentials */
if (!uid_eq(bprm->cred->uid, current_euid()) ||
!gid_eq(bprm->cred->gid, current_egid())) {
current->pdeath_signal = 0;
In commit 221af7f87b97 ("Split 'flush_old_exec' into two functions"), the comment about the point of no return should have stayed in flush_old_exec() since it refers to "bprm->mm = NULL;" line, but prior changes in commits c89681ed7d0e ("remove steal_locks()"), and fd8328be874f ("sanitize handling of shared descriptor tables in failing execve()") made it look like it meant the current->sas_ss_sp line instead. The comment was referring to the fact that once bprm->mm is NULL, all failures from a binfmt load_binary hook (e.g. load_elf_binary), will get SEGV raised against current. Move this comment and expand the explanation a bit, putting it above the assignment this time, and add details about the true nature of "point of no return" being the call to flush_old_exec() itself. This also removes an erroneous commet about when credentials are being installed. That has its own dedicated function, install_exec_creds(), which carries a similar (and correct) comment, so remove the bogus comment where installation is not actually happening. Cc: David Howells <dhowells@redhat.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: "Eric W. Biederman" <ebiederm@xmission.com> Acked-by: Serge Hallyn <serge@hallyn.com> --- fs/exec.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)