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authorOleg Nesterov <oleg@redhat.com>2014-01-23 15:55:50 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-01-23 16:37:02 -0800
commit9e00cdb091b008cb3c78192651180896de412a63 (patch)
tree58b9c75f95f3fbd91d66f16f00879652b1bb1fc4 /fs/exec.c
parent83f62a2eacb1d6945c78523f20e0c34b5d94913c (diff)
downloadlinux-9e00cdb091b008cb3c78192651180896de412a63.tar.gz
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/exec.c')
-rw-r--r--fs/exec.c29
1 files changed, 8 insertions, 21 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 81ae6212187..389fe7b0ba1 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: