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author | Oleg Nesterov <oleg@redhat.com> | 2014-01-23 15:55:50 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-01-23 16:37:02 -0800 |
commit | 9e00cdb091b008cb3c78192651180896de412a63 (patch) | |
tree | 58b9c75f95f3fbd91d66f16f00879652b1bb1fc4 /fs | |
parent | 83f62a2eacb1d6945c78523f20e0c34b5d94913c (diff) | |
download | linux-9e00cdb091b008cb3c78192651180896de412a63.tar.gz linux-9e00cdb091b008cb3c78192651180896de412a63.tar.bz2 linux-9e00cdb091b008cb3c78192651180896de412a63.zip |
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>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/exec.c | 29 |
1 files changed, 8 insertions, 21 deletions
diff --git a/fs/exec.c b/fs/exec.c index 81ae6212187a..389fe7b0ba14 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1223,11 +1223,10 @@ EXPORT_SYMBOL(install_exec_creds); * - 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 @@ static int check_unsafe_exec(struct linux_binprm *bprm) } 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 @@ static int do_execve_common(const char *filename, struct linux_binprm *bprm; struct file *file; struct files_struct *displaced; - bool clear_in_exec; int retval; /* @@ -1485,10 +1476,7 @@ static int do_execve_common(const char *filename, 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_file: } out_unmark: - if (clear_in_exec) - current->fs->in_exec = 0; + current->fs->in_exec = 0; current->in_execve = 0; out_free: |