From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: exec: move path_noexec() check earlier
The path_noexec() check, like the regular file check, was happening too
late, letting LSMs see impossible execve()s. Check it earlier as well in
may_open() 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,
.acc_mode = MAY_EXEC,
...
do_filp_open(dfd, filename, open_flags)
path_openat(nameidata, open_flags, flags)
file = alloc_empty_file(open_flags, current_cred());
do_open(nameidata, file, open_flags)
may_open(path, acc_mode, open_flag)
/* new location of MAY_EXEC vs path_noexec() test */
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 */
Link: http://lkml.kernel.org/r/20200605160013.3954297-4-keescook@xxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Aleksa Sarai <cyphar@xxxxxxxxxx>
Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Eric Biggers <ebiggers3@xxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/exec.c | 12 ++++--------
fs/namei.c | 4 ++++
2 files changed, 8 insertions(+), 8 deletions(-)
--- a/fs/exec.c~exec-move-path_noexec-check-earlier
+++ a/fs/exec.c
@@ -147,10 +147,8 @@ SYSCALL_DEFINE1(uselib, const char __use
* and check again at the very end too.
*/
error = -EACCES;
- if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
- goto exit;
-
- if (path_noexec(&file->f_path))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
+ path_noexec(&file->f_path)))
goto exit;
fsnotify_open(file);
@@ -919,10 +917,8 @@ static struct file *do_open_execat(int f
* and check again at the very end too.
*/
err = -EACCES;
- if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
- goto exit;
-
- if (path_noexec(&file->f_path))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
+ path_noexec(&file->f_path)))
goto exit;
err = deny_write_access(file);
--- a/fs/namei.c~exec-move-path_noexec-check-earlier
+++ a/fs/namei.c
@@ -2863,6 +2863,10 @@ static int may_open(const struct path *p
return -EACCES;
flag &= ~O_TRUNC;
break;
+ case S_IFREG:
+ if ((acc_mode & MAY_EXEC) && path_noexec(path))
+ return -EACCES;
+ break;
}
error = inode_permission(inode, MAY_OPEN | acc_mode);
_
