The patch titled
Subject: exec: relocate S_ISREG() check
has been added to the -mm tree. Its filename is
exec-relocate-s_isreg-check.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/exec-relocate-s_isreg-check.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/exec-relocate-s_isreg-check.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: exec: relocate S_ISREG() check
The execve(2)/uselib(2) syscalls have always rejected non-regular files.
Recently, it was noticed that a deadlock was introduced when trying to
execute pipes, as the S_ISREG() test was happening too late. This was
fixed in commit 73601ea5b7b1 ("fs/open.c: allow opening only regular files
during execve()"), but it was added after inode_permission() had already
run, which meant LSMs could see bogus attempts to execute non-regular
files. Move the test earlier.
Also include a comment with the redundant S_ISREG() checks at the end of
execve(2)/uselib(2) to note that they are present to avoid any mistakes.
Finally, instead of dereferencing the inode, use dcache for S_ISREG()
test.
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 S_ISREG() 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)
/* old location of FMODE_EXEC vs S_ISREG() test */
security_file_open(f)
open()
Link: http://lkml.kernel.org/r/20200518055457.12302-3-keescook@xxxxxxxxxxxx
Fixes: 73601ea5b7b1 ("fs/open.c: allow opening only regular files during execve()")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
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 | 8 ++++++++
fs/namei.c | 4 ++++
fs/open.c | 6 ------
3 files changed, 12 insertions(+), 6 deletions(-)
--- a/fs/exec.c~exec-relocate-s_isreg-check
+++ a/fs/exec.c
@@ -139,6 +139,10 @@ SYSCALL_DEFINE1(uselib, const char __use
if (IS_ERR(file))
goto out;
+ /*
+ * do_open() has already checked for this, 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;
@@ -884,6 +888,10 @@ static struct file *do_open_execat(int f
if (IS_ERR(file))
goto out;
+ /*
+ * do_open() has already checked for this, 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;
--- a/fs/namei.c~exec-relocate-s_isreg-check
+++ a/fs/namei.c
@@ -3212,6 +3212,10 @@ 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))
+ return -EACCES;
+
do_truncate = false;
acc_mode = op->acc_mode;
if (file->f_mode & FMODE_CREATED) {
--- a/fs/open.c~exec-relocate-s_isreg-check
+++ a/fs/open.c
@@ -752,12 +752,6 @@ static int do_dentry_open(struct file *f
return 0;
}
- /* Any file opened for execve()/uselib() has to be a regular file. */
- if (unlikely(f->f_flags & FMODE_EXEC && !S_ISREG(inode->i_mode))) {
- error = -EACCES;
- goto cleanup_file;
- }
-
if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
error = get_write_access(inode);
if (unlikely(error))
_
Patches currently in -mm which might be from keescook@xxxxxxxxxxxx are
exec-change-uselib2-is_sreg-failure-to-eacces.patch
exec-relocate-s_isreg-check.patch
exec-relocate-path_noexec-check.patch
fs-include-fmode_exec-when-converting-flags-to-f_mode.patch
