[PATCH] CRED: Take cred_exec_mutex in compat_do_execve() and fix error handling in do_execve()

[David Howells <dhowells@redhat.com>]

Take cred_exec_mutex in compat_do_execve().  This reflects what do_execve()
does.  The mutex protects credentials calculation against PTRACE_ATTACH needing
to alter it mid-exec.

Also fix the error handling in do_execve().  The mutex needs to be unlocked if
an error occurs after it is taken, but before the install_exec_creds()
released it.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/compat.c |   12 ++++++++++--
 fs/exec.c   |   12 ++++++++----
 2 files changed, 18 insertions(+), 6 deletions(-)


diff --git a/fs/compat.c b/fs/compat.c
index 2dde882..af24b8a 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1360,15 +1360,20 @@ int compat_do_execve(char * filename,
 	if (!bprm)
 		goto out_ret;
 
+	retval = mutex_lock_interruptible(&current->cred_exec_mutex);
+	if (retval < 0)
+		goto out_free;
+
+	retval = -ENOMEM;
 	bprm->cred = prepare_exec_creds();
 	if (!bprm->cred)
-		goto out_free;
+		goto out_unlock;
 	check_unsafe_exec(bprm);
 
 	file = open_exec(filename);
 	retval = PTR_ERR(file);
 	if (IS_ERR(file))
-		goto out_free;
+		goto out_unlock;
 
 	sched_exec();
 
@@ -1423,6 +1428,9 @@ out_file:
 		fput(bprm->file);
 	}
 
+out_unlock:
+	mutex_unlock(&current->cred_exec_mutex);
+
 out_free:
 	free_bprm(bprm);
 
diff --git a/fs/exec.c b/fs/exec.c
index a7633e5..4b31a72 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1308,18 +1308,18 @@ int do_execve(char * filename,
 
 	retval = mutex_lock_interruptible(&current->cred_exec_mutex);
 	if (retval < 0)
-		goto out_kfree;
+		goto out_free;
 
 	retval = -ENOMEM;
 	bprm->cred = prepare_exec_creds();
 	if (!bprm->cred)
-		goto out_kfree;
+		goto out_unlock;
 	check_unsafe_exec(bprm);
 
 	file = open_exec(filename);
 	retval = PTR_ERR(file);
 	if (IS_ERR(file))
-		goto out_kfree;
+		goto out_unlock;
 
 	sched_exec();
 
@@ -1376,7 +1376,11 @@ out_file:
 		allow_write_access(bprm->file);
 		fput(bprm->file);
 	}
-out_kfree:
+
+out_unlock:
+	mutex_unlock(&current->cred_exec_mutex);
+
+out_free:
 	free_bprm(bprm);
 
 out_files: