The path_noexec() check, like the regular file check, was happening too
late, letting LSMs see impossible execve()s. Check it earlier as well
and collect the redundant fs/exec.c path_noexec() test under the same
robustness comment as the S_ISREG() check.
My notes on the call path, and related arguments, checks, etc:
do_open_execat()
struct open_flags open_exec_flags = {
.open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC, ...
do_filp_open(dfd, filename, open_flags)
path_openat(nameidata, open_flags, flags)
/* f_mode populated from open_flags in alloc_empty_file() */
file = alloc_empty_file(open_flags, current_cred());
do_open(nameidata, file, open_flags)
/* new location of FMODE_EXEC vs path_noexec() test */
may_open(path, acc_mode, open_flag)
inode_permission(inode, MAY_OPEN | acc_mode)
security_inode_permission(inode, acc_mode)
vfs_open(path, file)
do_dentry_open(file, path->dentry->d_inode, open)
security_file_open(f)
open()
/* old location of path_noexec() test */
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
fs/exec.c | 6 ++----
fs/namei.c | 5 +++--
2 files changed, 5 insertions(+), 6 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index f0c80a8b9ccd..a34093323aa1 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -140,13 +140,12 @@ SYSCALL_DEFINE1(uselib, const char __user *, library)
goto out;
/*
- * do_open() has already checked for this, but we can be extra
+ * do_open() has already checked for these, but we can be extra
* cautious and check again at the very end too.
*/
error = -EACCES;
if (!S_ISREG(file_inode(file)->i_mode))
goto exit;
-
if (path_noexec(&file->f_path))
goto exit;
@@ -865,13 +864,12 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags)
goto out;
/*
- * do_open() has already checked for this, but we can be extra
+ * do_open() has already checked for these, but we can be extra
* cautious and check again at the very end too.
*/
err = -EACCES;
if (!S_ISREG(file_inode(file)->i_mode))
goto exit;
-
if (path_noexec(&file->f_path))
goto exit;
diff --git a/fs/namei.c b/fs/namei.c
index b9408aacaaa4..6bb1b6624bad 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3212,8 +3212,9 @@ static int do_open(struct nameidata *nd,
if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
return -ENOTDIR;
- /* Any file opened for execution has to be a regular file. */
- if ((file->f_flags & FMODE_EXEC) && !d_is_reg(nd->path.dentry))
+ /* Opening for execution requires a regular file on an exec mnt. */
+ if ((file->f_flags & FMODE_EXEC) && (!d_is_reg(nd->path.dentry) ||
+ path_noexec(&nd->path)))
return -EACCES;
do_truncate = false;
--
2.20.1
