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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id t25sm4143998pgo.7.2020.05.17.22.55.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 17 May 2020 22:55:03 -0700 (PDT) From: Kees Cook To: Al Viro Cc: Kees Cook , Andrew Morton , Tetsuo Handa , Eric Biggers , Dmitry Vyukov , linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/4] exec: Relocate S_ISREG() check Date: Sun, 17 May 2020 22:54:55 -0700 Message-Id: <20200518055457.12302-3-keescook@chromium.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200518055457.12302-1-keescook@chromium.org> References: <20200518055457.12302-1-keescook@chromium.org> MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.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 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() Signed-off-by: Kees Cook --- fs/exec.c | 8 ++++++++ fs/namei.c | 4 ++++ fs/open.c | 6 ------ 3 files changed, 12 insertions(+), 6 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 30735ce1dc0e..f0c80a8b9ccd 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -139,6 +139,10 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) 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; @@ -860,6 +864,10 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) 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; diff --git a/fs/namei.c b/fs/namei.c index a320371899cf..b9408aacaaa4 100644 --- a/fs/namei.c +++ b/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) { 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))