From: Kees Cook <keescook@chromium.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Aleksa Sarai <cyphar@cyphar.com>,
Christian Brauner <christian.brauner@ubuntu.com>,
Dmitry Vyukov <dvyukov@google.com>,
Eric Biggers <ebiggers3@gmail.com>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 2/3] exec: Move S_ISREG() check earlier
Date: Fri, 5 Jun 2020 09:00:12 -0700 [thread overview]
Message-ID: <20200605160013.3954297-3-keescook@chromium.org> (raw)
In-Reply-To: <20200605160013.3954297-1-keescook@chromium.org>
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 into the other inode type checks (which already look
for other pathological conditions[1]). Since there is no need to use
FMODE_EXEC while we still have access to "acc_mode", also switch the
test to MAY_EXEC.
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.
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 S_ISREG() 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)
/* old location of FMODE_EXEC vs S_ISREG() test */
security_file_open(f)
open()
[1] https://lore.kernel.org/lkml/202006041910.9EF0C602@keescook/
Signed-off-by: Kees Cook <keescook@chromium.org>
---
fs/exec.c | 14 ++++++++++++--
fs/namei.c | 6 ++++--
fs/open.c | 6 ------
3 files changed, 16 insertions(+), 10 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 30735ce1dc0e..2b708629dcd6 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -139,8 +139,13 @@ SYSCALL_DEFINE1(uselib, const char __user *, library)
if (IS_ERR(file))
goto out;
+ /*
+ * may_open() has already checked for this, so it should be
+ * impossible to trip now. But we need to be extra cautious
+ * and check again at the very end too.
+ */
error = -EACCES;
- if (!S_ISREG(file_inode(file)->i_mode))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
goto exit;
if (path_noexec(&file->f_path))
@@ -860,8 +865,13 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags)
if (IS_ERR(file))
goto out;
+ /*
+ * may_open() has already checked for this, so it should be
+ * impossible to trip now. But we need to be extra cautious
+ * and check again at the very end too.
+ */
err = -EACCES;
- if (!S_ISREG(file_inode(file)->i_mode))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
goto exit;
if (path_noexec(&file->f_path))
diff --git a/fs/namei.c b/fs/namei.c
index a320371899cf..0a759b68d66e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2835,16 +2835,18 @@ static int may_open(const struct path *path, int acc_mode, int flag)
case S_IFLNK:
return -ELOOP;
case S_IFDIR:
- if (acc_mode & MAY_WRITE)
+ if (acc_mode & (MAY_WRITE | MAY_EXEC))
return -EISDIR;
break;
case S_IFBLK:
case S_IFCHR:
if (!may_open_dev(path))
return -EACCES;
- /*FALLTHRU*/
+ fallthrough;
case S_IFIFO:
case S_IFSOCK:
+ if (acc_mode & MAY_EXEC)
+ return -EACCES;
flag &= ~O_TRUNC;
break;
}
diff --git a/fs/open.c b/fs/open.c
index 719b320ede52..bb16e4e3cd57 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -753,12 +753,6 @@ 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))
--
2.25.1
next prev parent reply other threads:[~2020-06-05 16:00 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-05 16:00 [PATCH v2 0/3] Relocate execve() sanity checks Kees Cook
2020-06-05 16:00 ` [PATCH v2 1/3] exec: Change uselib(2) IS_SREG() failure to EACCES Kees Cook
2020-06-05 16:00 ` Kees Cook [this message]
2020-08-13 14:13 ` [PATCH v2 2/3] exec: Move S_ISREG() check earlier Marc Zyngier
2020-08-13 17:13 ` Kees Cook
2020-06-05 16:00 ` [PATCH v2 3/3] exec: Move path_noexec() " Kees Cook
2020-06-06 0:40 ` [PATCH v2 0/3] Relocate execve() sanity checks Andrew Morton
2020-06-06 1:45 ` Kees Cook
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