From 633fb6ac39801514613fbe050db6abdc3fe744d5 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 11 Aug 2020 18:36:26 -0700 Subject: exec: move S_ISREG() check earlier 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 Signed-off-by: Andrew Morton Cc: Aleksa Sarai Cc: Alexander Viro Cc: Christian Brauner Cc: Dmitry Vyukov Cc: Eric Biggers Cc: Tetsuo Handa Link: http://lkml.kernel.org/r/20200605160013.3954297-3-keescook@chromium.org Signed-off-by: Linus Torvalds --- fs/exec.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) (limited to 'fs/exec.c') diff --git a/fs/exec.c b/fs/exec.c index c56aad307069..cc7ec7b9000b 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -141,8 +141,13 @@ 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)) @@ -908,8 +913,13 @@ 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)) -- cgit v1.2.3