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 <keescook@xxxxxxxxxxxx>
---
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))
--
2.20.1
