Merge tag 'vfs-6.13.exec.deny_write_access.revert' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull deny_write_access revert from Christian Brauner:
 "It turns out that the mold linker relies on the deny_write_access()
  mechanism for executables.

  The mold linker tries to open a file for writing and if ETXTBSY is
  returned mold falls back to creating a new file"

* tag 'vfs-6.13.exec.deny_write_access.revert' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  Revert "fs: don't block i_writecount during exec"

1 files changed, 23 insertions, 3 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index f253e81d0c28..1450b461d196 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -621,6 +621,12 @@ static void dup_mm_exe_file(struct mm_struct *mm, struct mm_struct *oldmm)
 
 	exe_file = get_mm_exe_file(oldmm);
 	RCU_INIT_POINTER(mm->exe_file, exe_file);
+	/*
+	 * We depend on the oldmm having properly denied write access to the
+	 * exe_file already.
+	 */
+	if (exe_file && deny_write_access(exe_file))
+		pr_warn_once("deny_write_access() failed in %s\n", __func__);
 }
 
 #ifdef CONFIG_MMU
@@ -1413,11 +1419,20 @@ int set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 	 */
 	old_exe_file = rcu_dereference_raw(mm->exe_file);
 
-	if (new_exe_file)
+	if (new_exe_file) {
+		/*
+		 * We expect the caller (i.e., sys_execve) to already denied
+		 * write access, so this is unlikely to fail.
+		 */
+		if (unlikely(deny_write_access(new_exe_file)))
+			return -EACCES;
 		get_file(new_exe_file);
+	}
 	rcu_assign_pointer(mm->exe_file, new_exe_file);
-	if (old_exe_file)
+	if (old_exe_file) {
+		allow_write_access(old_exe_file);
 		fput(old_exe_file);
+	}
 	return 0;
 }
 
@@ -1456,6 +1471,9 @@ int replace_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 			return ret;
 	}
 
+	ret = deny_write_access(new_exe_file);
+	if (ret)
+		return -EACCES;
 	get_file(new_exe_file);
 
 	/* set the new file */
@@ -1464,8 +1482,10 @@ int replace_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 	rcu_assign_pointer(mm->exe_file, new_exe_file);
 	mmap_write_unlock(mm);
 
-	if (old_exe_file)
+	if (old_exe_file) {
+		allow_write_access(old_exe_file);
 		fput(old_exe_file);
+	}
 	return 0;
 }