exec:check_unsafe_exec: kill the dead -EAGAIN and clear_in_exec logic
fs_struct->in_exec == T means that this ->fs is used by a single process
(thread group), and one of the treads does do_execve().
To avoid the mt-exec races this code has the following complications:
1. check_unsafe_exec() returns -EBUSY if ->in_exec was
already set by another thread.
2. do_execve_common() records "clear_in_exec" to ensure
that the error path can only clear ->in_exec if it was
set by current.
However, after 9b1bf12d5d51 "signals: move cred_guard_mutex from
task_struct to signal_struct" we do not need these complications:
1. We can't race with our sub-thread, this is called under
per-process ->cred_guard_mutex. And we can't race with
another CLONE_FS task, we already checked that this fs
is not shared.
We can remove the dead -EAGAIN logic.
2. "out_unmark:" in do_execve_common() is either called
under ->cred_guard_mutex, or after de_thread() which
kills other threads, so we can't race with sub-thread
which could set ->in_exec. And if ->fs is shared with
another process ->in_exec should be false anyway.
We can clear in_exec unconditionally.
This also means that check_unsafe_exec() can be void.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/exec.c b/fs/exec.c
index 81ae621..389fe7b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1223,11 +1223,10 @@
* - the caller must hold ->cred_guard_mutex to protect against
* PTRACE_ATTACH
*/
-static int check_unsafe_exec(struct linux_binprm *bprm)
+static void check_unsafe_exec(struct linux_binprm *bprm)
{
struct task_struct *p = current, *t;
unsigned n_fs;
- int res = 0;
if (p->ptrace) {
if (p->ptrace & PT_PTRACE_CAP)
@@ -1253,22 +1252,15 @@
}
rcu_read_unlock();
- if (p->fs->users > n_fs) {
+ if (p->fs->users > n_fs)
bprm->unsafe |= LSM_UNSAFE_SHARE;
- } else {
- res = -EAGAIN;
- if (!p->fs->in_exec) {
- p->fs->in_exec = 1;
- res = 1;
- }
- }
+ else
+ p->fs->in_exec = 1;
spin_unlock(&p->fs->lock);
-
- return res;
}
-/*
- * Fill the binprm structure from the inode.
+/*
+ * Fill the binprm structure from the inode.
* Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes
*
* This may be called multiple times for binary chains (scripts for example).
@@ -1453,7 +1445,6 @@
struct linux_binprm *bprm;
struct file *file;
struct files_struct *displaced;
- bool clear_in_exec;
int retval;
/*
@@ -1485,10 +1476,7 @@
if (retval)
goto out_free;
- retval = check_unsafe_exec(bprm);
- if (retval < 0)
- goto out_free;
- clear_in_exec = retval;
+ check_unsafe_exec(bprm);
current->in_execve = 1;
file = open_exec(filename);
@@ -1558,8 +1546,7 @@
}
out_unmark:
- if (clear_in_exec)
- current->fs->in_exec = 0;
+ current->fs->in_exec = 0;
current->in_execve = 0;
out_free: