1 files changed, 146 insertions, 50 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 9ea3a775d51e..d3081c8f7c10 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -30,11 +30,13 @@
 #include <linux/mm.h>
 #include <linux/stat.h>
 #include <linux/fcntl.h>
+#include <linux/futex.h>
 #include <linux/swap.h>
 #include <linux/string.h>
 #include <linux/init.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/coredump.h>
+#include <linux/sched/exec_state.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/numa_balancing.h>
 #include <linux/sched/task.h>
@@ -263,6 +265,9 @@ static int bprm_mm_init(struct linux_binprm *bprm)
 	if (!mm)
 		goto err;
 
+	/* Staged for would_dump() narrowing; consumed by begin_new_exec(). */
+	bprm->user_ns = get_user_ns(current_user_ns());
+
 	/* Save current stack limit for all calculations made during exec. */
 	task_lock(current->group_leader);
 	bprm->rlim_stack = current->signal->rlim[RLIMIT_STACK];
@@ -736,7 +741,7 @@ int transfer_args_to_stack(struct linux_binprm *bprm,
 	stop = bprm->p >> PAGE_SHIFT;
 	sp = *sp_location;
 
-	for (index = MAX_ARG_PAGES - 1; index >= stop; index--) {
+	for (index = MAX_ARG_PAGES; index-- > stop; ) {
 		unsigned int offset = index == stop ? bprm->p & ~PAGE_MASK : 0;
 		char *src = kmap_local_page(bprm->page[index]) + offset;
 		sp -= PAGE_SIZE - offset;
@@ -832,18 +837,26 @@ EXPORT_SYMBOL(read_code);
 /*
  * Maps the mm_struct mm into the current task struct.
  * On success, this function returns with exec_update_lock
- * held for writing.
+ * held for writing. The replaced address space is stashed in
+ * bprm->old_mm for setup_new_exec() to release outside the lock.
  */
-static int exec_mmap(struct mm_struct *mm)
+static int exec_mmap(struct linux_binprm *bprm)
 {
+	struct task_exec_state *exec_state __free(put_task_exec_state) = NULL;
+	struct mm_struct *mm = bprm->mm;
 	struct task_struct *tsk;
 	struct mm_struct *old_mm, *active_mm;
 	int ret;
 
+	exec_state = alloc_task_exec_state(bprm->user_ns);
+	if (!exec_state)
+		return -ENOMEM;
+
 	/* Notify parent that we're no longer interested in the old VM */
 	tsk = current;
 	old_mm = current->mm;
-	exec_mm_release(tsk, old_mm);
+	/* Clean up futexes and release the mm */
+	mm_exit_exec_release(tsk, old_mm);
 
 	ret = down_write_killable(&tsk->signal->exec_update_lock);
 	if (ret)
@@ -870,6 +883,7 @@ static int exec_mmap(struct mm_struct *mm)
 	tsk->active_mm = mm;
 	tsk->mm = mm;
 	mm_init_cid(mm, tsk);
+	exec_state = task_exec_state_replace(tsk, exec_state);
 	/*
 	 * This prevents preemption while active_mm is being loaded and
 	 * it and mm are being updated, which could cause problems for
@@ -888,15 +902,23 @@ static int exec_mmap(struct mm_struct *mm)
 	if (old_mm) {
 		mmap_read_unlock(old_mm);
 		BUG_ON(active_mm != old_mm);
-		setmax_mm_hiwater_rss(&tsk->signal->maxrss, old_mm);
-		mm_update_next_owner(old_mm);
-		mmput(old_mm);
-		return 0;
+		/* Defer teardown to setup_new_exec(), outside the exec locks. */
+		bprm->old_mm = old_mm;
+	} else {
+		mmdrop_lazy_tlb(active_mm);
 	}
-	mmdrop_lazy_tlb(active_mm);
+	futex_exec_done(tsk);
 	return 0;
 }
 
+/* Release the address space replaced by exec, outside the exec locks. */
+static void exec_mm_put_old(struct mm_struct *old_mm)
+{
+	setmax_mm_hiwater_rss(&current->signal->maxrss, old_mm);
+	mm_update_next_owner(old_mm);
+	mmput(old_mm);
+}
+
 static int de_thread(struct task_struct *tsk)
 {
 	struct signal_struct *sig = tsk->signal;
@@ -1074,7 +1096,7 @@ static int unshare_sighand(struct task_struct *me)
  */
 void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
 {
-	size_t len = min(strlen(buf), sizeof(tsk->comm) - 1);
+	size_t len = strnlen(buf, sizeof(tsk->comm) - 1);
 
 	trace_task_rename(tsk, buf);
 	memcpy(tsk->comm, buf, len);
@@ -1083,6 +1105,17 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
 }
 
 /*
+ * The file the process presents as: its exe link and comm. A transparent
+ * dispatch presents as the binary, which is bprm->executable.
+ */
+static struct file *bprm_identity_file(const struct linux_binprm *bprm)
+{
+	if (bprm->interp_flags & BINPRM_FLAGS_TRANSPARENT_INTERP)
+		return bprm->executable;
+	return bprm->file;
+}
+
+/*
  * 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
@@ -1093,6 +1126,10 @@ int begin_new_exec(struct linux_binprm * bprm)
 	struct task_struct *me = current;
 	int retval;
 
+	/* A pending PT_INTERP substitution this format cannot consume. */
+	if (bprm->loader)
+		return -ENOEXEC;
+
 	/* Once we are committed compute the creds */
 	retval = bprm_creds_from_file(bprm);
 	if (retval)
@@ -1128,11 +1165,25 @@ int begin_new_exec(struct linux_binprm * bprm)
 		goto out;
 
 	/*
+	 * We have to apply CLOEXEC before we change whether the process is
+	 * dumpable (in setup_new_exec) to avoid a race with a process in userspace
+	 * trying to access the should-be-closed file descriptors of a process
+	 * undergoing exec(2).
+	 *
+	 * This can block on filesystem ->flush() handlers, including waiting
+	 * for FUSE daemons, so do it before exec_mmap takes the
+	 * exec_update_lock.
+	 * This must happen after the point of no return, and after unsharing
+	 * the FD table.
+	 */
+	do_close_on_exec(me->files);
+
+	/*
 	 * Must be called _before_ exec_mmap() as bprm->mm is
 	 * not visible until then. Doing it here also ensures
 	 * we don't race against replace_mm_exe_file().
 	 */
-	retval = set_mm_exe_file(bprm->mm, bprm->file);
+	retval = set_mm_exe_file(bprm->mm, bprm_identity_file(bprm));
 	if (retval)
 		goto out;
 
@@ -1145,7 +1196,7 @@ int begin_new_exec(struct linux_binprm * bprm)
 	 * Release all of the old mmap stuff
 	 */
 	acct_arg_size(bprm, 0);
-	retval = exec_mmap(bprm->mm);
+	retval = exec_mmap(bprm);
 	if (retval)
 		goto out;
 
@@ -1177,14 +1228,6 @@ int begin_new_exec(struct linux_binprm * bprm)
 
 	clear_syscall_work_syscall_user_dispatch(me);
 
-	/*
-	 * We have to apply CLOEXEC before we change whether the process is
-	 * dumpable (in setup_new_exec) to avoid a race with a process in userspace
-	 * trying to access the should-be-closed file descriptors of a process
-	 * undergoing exec(2).
-	 */
-	do_close_on_exec(me->files);
-
 	if (bprm->secureexec) {
 		/* Make sure parent cannot signal privileged process. */
 		me->pdeath_signal = 0;
@@ -1210,9 +1253,9 @@ int begin_new_exec(struct linux_binprm * bprm)
 	if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP ||
 	    !(uid_eq(current_euid(), current_uid()) &&
 	      gid_eq(current_egid(), current_gid())))
-		set_dumpable(current->mm, suid_dumpable);
+		task_exec_state_set_dumpable(suid_dumpable);
 	else
-		set_dumpable(current->mm, SUID_DUMP_USER);
+		task_exec_state_set_dumpable(TASK_DUMPABLE_OWNER);
 
 	perf_event_exec();
 
@@ -1222,6 +1265,8 @@ int begin_new_exec(struct linux_binprm * bprm)
 	 * Let's fix it up to be something reasonable.
 	 */
 	if (bprm->comm_from_dentry) {
+		struct file *comm_file = bprm_identity_file(bprm);
+
 		/*
 		 * Hold RCU lock to keep the name from being freed behind our back.
 		 * Use acquire semantics to make sure the terminating NUL from
@@ -1231,7 +1276,7 @@ int begin_new_exec(struct linux_binprm * bprm)
 		 * detecting a concurrent rename and just want a terminated name.
 		 */
 		rcu_read_lock();
-		__set_task_comm(me, smp_load_acquire(&bprm->file->f_path.dentry->d_name.name),
+		__set_task_comm(me, smp_load_acquire(&comm_file->f_path.dentry->d_name.name),
 				true);
 		rcu_read_unlock();
 	} else {
@@ -1261,7 +1306,7 @@ int begin_new_exec(struct linux_binprm * bprm)
 	 * wait until new credentials are committed
 	 * by commit_creds() above
 	 */
-	if (get_dumpable(me->mm) != SUID_DUMP_USER)
+	if (task_exec_state_get_dumpable(me) != TASK_DUMPABLE_OWNER)
 		perf_event_exit_task(me);
 	/*
 	 * cred_guard_mutex must be held at least to this point to prevent
@@ -1272,10 +1317,17 @@ int begin_new_exec(struct linux_binprm * bprm)
 
 	/* Pass the opened binary to the interpreter. */
 	if (bprm->have_execfd) {
-		retval = FD_ADD(0, bprm->executable);
-		if (retval < 0)
-			goto out_unlock;
+		struct file *executable = bprm->executable;
+
+		/* mm->exe_file carries its own write denial now so drop it. */
+		exe_file_allow_write_access(executable);
 		bprm->executable = NULL;
+		retval = FD_ADD(0, executable);
+		if (retval < 0) {
+			/* The reference was not consumed. */
+			fput(executable);
+			goto out_unlock;
+		}
 		bprm->execfd = retval;
 	}
 	return 0;
@@ -1298,14 +1350,14 @@ void would_dump(struct linux_binprm *bprm, struct file *file)
 		struct user_namespace *old, *user_ns;
 		bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
 
-		/* Ensure mm->user_ns contains the executable */
-		user_ns = old = bprm->mm->user_ns;
+		/* Ensure bprm->user_ns contains the executable. */
+		user_ns = old = bprm->user_ns;
 		while ((user_ns != &init_user_ns) &&
 		       !privileged_wrt_inode_uidgid(user_ns, idmap, inode))
 			user_ns = user_ns->parent;
 
 		if (old != user_ns) {
-			bprm->mm->user_ns = get_user_ns(user_ns);
+			bprm->user_ns = get_user_ns(user_ns);
 			put_user_ns(old);
 		}
 	}
@@ -1328,6 +1380,12 @@ void setup_new_exec(struct linux_binprm * bprm)
 	me->mm->task_size = TASK_SIZE;
 	up_write(&me->signal->exec_update_lock);
 	mutex_unlock(&me->signal->cred_guard_mutex);
+
+	/* The exec locks are dropped: release the old address space now. */
+	if (bprm->old_mm) {
+		exec_mm_put_old(bprm->old_mm);
+		bprm->old_mm = NULL;
+	}
 }
 EXPORT_SYMBOL(setup_new_exec);
 
@@ -1369,12 +1427,47 @@ static void do_close_execat(struct file *file)
 	fput(file);
 }
 
+/**
+ * bprm_open_interpreter - open the interpreter the binary asks for
+ * @bprm: binary that is being executed
+ * @path: the interpreter path named in the binary's PT_INTERP
+ *
+ * A binfmt_misc loader entry substitutes for the interpreter the binary
+ * names. Hand out the stashed substitute if there is one and open @path
+ * if there is not. The caller owns the reference either way and releases
+ * it like any other open_exec() one.
+ *
+ * Return: the interpreter on success, an ERR_PTR on failure
+ */
+struct file *bprm_open_interpreter(struct linux_binprm *bprm, const char *path)
+{
+	if (bprm->loader)
+		return no_free_ptr(bprm->loader);
+	return open_exec(path);
+}
+
+/**
+ * bprm_drop_loader - discard a PT_INTERP substitute that does not apply
+ * @bprm: binary that is being executed
+ *
+ * A binary without PT_INTERP has nothing to substitute for, so drop the
+ * override and let the binary load natively rather than have
+ * begin_new_exec() refuse it. A no-op once bprm_open_interpreter() took
+ * the substitute.
+ */
+void bprm_drop_loader(struct linux_binprm *bprm)
+{
+	do_close_execat(no_free_ptr(bprm->loader));
+}
+
 static void free_bprm(struct linux_binprm *bprm)
 {
 	if (bprm->mm) {
 		acct_arg_size(bprm, 0);
 		mmput(bprm->mm);
 	}
+	if (bprm->user_ns)
+		put_user_ns(bprm->user_ns);
 	free_arg_pages(bprm);
 	if (bprm->cred) {
 		/* in case exec fails before de_thread() succeeds */
@@ -1382,12 +1475,20 @@ static void free_bprm(struct linux_binprm *bprm)
 		mutex_unlock(&current->signal->cred_guard_mutex);
 		abort_creds(bprm->cred);
 	}
+	/* exec swapped the mm but failed before setup_new_exec() freed it */
+	if (bprm->old_mm)
+		exec_mm_put_old(bprm->old_mm);
+	/* An unconsumed PT_INTERP substitute from a binfmt_misc loader entry. */
+	bprm_drop_loader(bprm);
 	do_close_execat(bprm->file);
-	if (bprm->executable)
-		fput(bprm->executable);
+	do_close_execat(bprm->executable);
 	/* If a binfmt changed the interp, free it. */
 	if (bprm->interp != bprm->filename)
 		kfree(bprm->interp);
+	kfree(bprm->bpf_interp);
+	if (bprm->bpf_interp_file)
+		fput(bprm->bpf_interp_file);
+	kfree(bprm->bpf_interp_arg);
 	kfree(bprm->fdpath);
 	kfree(bprm);
 }
@@ -1687,7 +1788,7 @@ static int exec_binprm(struct linux_binprm *bprm)
 	old_vpid = task_pid_nr_ns(current, task_active_pid_ns(current->parent));
 	rcu_read_unlock();
 
-	/* This allows 4 levels of binfmt rewrites before failing hard. */
+	/* This allows 5 levels of binfmt rewrites before failing hard. */
 	for (depth = 0;; depth++) {
 		struct file *exec;
 		if (depth > 5)
@@ -1699,19 +1800,23 @@ static int exec_binprm(struct linux_binprm *bprm)
 		if (!bprm->interpreter)
 			break;
 
+		/* A stashed PT_INTERP substitute belonged to the replaced file. */
+		bprm_drop_loader(bprm);
+
 		exec = bprm->file;
 		bprm->file = bprm->interpreter;
 		bprm->interpreter = NULL;
 
-		exe_file_allow_write_access(exec);
 		if (unlikely(bprm->have_execfd)) {
 			if (bprm->executable) {
-				fput(exec);
+				do_close_execat(exec);
 				return -ENOEXEC;
 			}
+			/* Kept for AT_EXECFD; the write denial rides along until hand-over. */
 			bprm->executable = exec;
-		} else
-			fput(exec);
+		} else {
+			do_close_execat(exec);
+		}
 	}
 
 	audit_bprm(bprm);
@@ -1905,17 +2010,6 @@ void set_binfmt(struct linux_binfmt *new)
 }
 EXPORT_SYMBOL(set_binfmt);
 
-/*
- * set_dumpable stores three-value SUID_DUMP_* into mm->flags.
- */
-void set_dumpable(struct mm_struct *mm, int value)
-{
-	if (WARN_ON((unsigned)value > SUID_DUMP_ROOT))
-		return;
-
-	__mm_flags_set_mask_dumpable(mm, value);
-}
-
 static inline struct user_arg_ptr native_arg(const char __user *const __user *p)
 {
 	return (struct user_arg_ptr){.ptr.native = p};
@@ -1975,9 +2069,11 @@ COMPAT_SYSCALL_DEFINE5(execveat, int, fd,
 static int proc_dointvec_minmax_coredump(const struct ctl_table *table, int write,
 		void *buffer, size_t *lenp, loff_t *ppos)
 {
-	int error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	int error, old = READ_ONCE(suid_dumpable);
+
+	error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 
-	if (!error && write)
+	if (!error && write && (old != READ_ONCE(suid_dumpable)))
 		validate_coredump_safety();
 	return error;
 }