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 9b1bf12d5d
"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>
This commit is contained in:
parent
83f62a2eac
commit
9e00cdb091
1 changed files with 8 additions and 21 deletions
29
fs/exec.c
29
fs/exec.c
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@ -1223,11 +1223,10 @@ EXPORT_SYMBOL(install_exec_creds);
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* - the caller must hold ->cred_guard_mutex to protect against
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* PTRACE_ATTACH
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*/
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static int check_unsafe_exec(struct linux_binprm *bprm)
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static void check_unsafe_exec(struct linux_binprm *bprm)
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{
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struct task_struct *p = current, *t;
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unsigned n_fs;
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int res = 0;
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if (p->ptrace) {
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if (p->ptrace & PT_PTRACE_CAP)
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@ -1253,22 +1252,15 @@ static int check_unsafe_exec(struct linux_binprm *bprm)
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}
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rcu_read_unlock();
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if (p->fs->users > n_fs) {
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if (p->fs->users > n_fs)
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bprm->unsafe |= LSM_UNSAFE_SHARE;
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} else {
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res = -EAGAIN;
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if (!p->fs->in_exec) {
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p->fs->in_exec = 1;
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res = 1;
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}
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}
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else
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p->fs->in_exec = 1;
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spin_unlock(&p->fs->lock);
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return res;
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}
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/*
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* Fill the binprm structure from the inode.
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/*
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* Fill the binprm structure from the inode.
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* Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes
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*
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* This may be called multiple times for binary chains (scripts for example).
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@ -1453,7 +1445,6 @@ static int do_execve_common(const char *filename,
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struct linux_binprm *bprm;
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struct file *file;
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struct files_struct *displaced;
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bool clear_in_exec;
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int retval;
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/*
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@ -1485,10 +1476,7 @@ static int do_execve_common(const char *filename,
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if (retval)
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goto out_free;
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retval = check_unsafe_exec(bprm);
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if (retval < 0)
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goto out_free;
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clear_in_exec = retval;
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check_unsafe_exec(bprm);
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current->in_execve = 1;
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file = open_exec(filename);
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@ -1558,8 +1546,7 @@ static int do_execve_common(const char *filename,
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}
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out_unmark:
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if (clear_in_exec)
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current->fs->in_exec = 0;
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current->fs->in_exec = 0;
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current->in_execve = 0;
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out_free:
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