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-rw-r--r--kernel/fork.c19
-rw-r--r--kernel/sys.c47
2 files changed, 41 insertions, 25 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 259202637531..0d23e76a0c61 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -711,15 +711,22 @@ EXPORT_SYMBOL_GPL(mmput);
*
* This changes mm's executable file (shown as symlink /proc/[pid]/exe).
*
- * Main users are mmput(), sys_execve() and sys_prctl(PR_SET_MM_MAP/EXE_FILE).
- * Callers prevent concurrent invocations: in mmput() nobody alive left,
- * in execve task is single-threaded, prctl holds mmap_sem exclusively.
+ * Main users are mmput() and sys_execve(). Callers prevent concurrent
+ * invocations: in mmput() nobody alive left, in execve task is single
+ * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the
+ * mm->exe_file, but does so without using set_mm_exe_file() in order
+ * to do avoid the need for any locks.
*/
void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
{
- struct file *old_exe_file = rcu_dereference_protected(mm->exe_file,
- !atomic_read(&mm->mm_users) || current->in_execve ||
- lockdep_is_held(&mm->mmap_sem));
+ struct file *old_exe_file;
+
+ /*
+ * It is safe to dereference the exe_file without RCU as
+ * this function is only called if nobody else can access
+ * this mm -- see comment above for justification.
+ */
+ old_exe_file = rcu_dereference_raw(mm->exe_file);
if (new_exe_file)
get_file(new_exe_file);
diff --git a/kernel/sys.c b/kernel/sys.c
index 3be344902316..a4e372b798a5 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1649,14 +1649,13 @@ SYSCALL_DEFINE1(umask, int, mask)
return mask;
}
-static int prctl_set_mm_exe_file_locked(struct mm_struct *mm, unsigned int fd)
+static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
{
struct fd exe;
+ struct file *old_exe, *exe_file;
struct inode *inode;
int err;
- VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
-
exe = fdget(fd);
if (!exe.file)
return -EBADF;
@@ -1680,15 +1679,22 @@ static int prctl_set_mm_exe_file_locked(struct mm_struct *mm, unsigned int fd)
/*
* Forbid mm->exe_file change if old file still mapped.
*/
+ exe_file = get_mm_exe_file(mm);
err = -EBUSY;
- if (mm->exe_file) {
+ if (exe_file) {
struct vm_area_struct *vma;
- for (vma = mm->mmap; vma; vma = vma->vm_next)
- if (vma->vm_file &&
- path_equal(&vma->vm_file->f_path,
- &mm->exe_file->f_path))
- goto exit;
+ down_read(&mm->mmap_sem);
+ for (vma = mm->mmap; vma; vma = vma->vm_next) {
+ if (!vma->vm_file)
+ continue;
+ if (path_equal(&vma->vm_file->f_path,
+ &exe_file->f_path))
+ goto exit_err;
+ }
+
+ up_read(&mm->mmap_sem);
+ fput(exe_file);
}
/*
@@ -1702,10 +1708,18 @@ static int prctl_set_mm_exe_file_locked(struct mm_struct *mm, unsigned int fd)
goto exit;
err = 0;
- set_mm_exe_file(mm, exe.file); /* this grabs a reference to exe.file */
+ /* set the new file, lockless */
+ get_file(exe.file);
+ old_exe = xchg(&mm->exe_file, exe.file);
+ if (old_exe)
+ fput(old_exe);
exit:
fdput(exe);
return err;
+exit_err:
+ up_read(&mm->mmap_sem);
+ fput(exe_file);
+ goto exit;
}
#ifdef CONFIG_CHECKPOINT_RESTORE
@@ -1840,10 +1854,9 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
user_auxv[AT_VECTOR_SIZE - 1] = AT_NULL;
}
- down_write(&mm->mmap_sem);
if (prctl_map.exe_fd != (u32)-1)
- error = prctl_set_mm_exe_file_locked(mm, prctl_map.exe_fd);
- downgrade_write(&mm->mmap_sem);
+ error = prctl_set_mm_exe_file(mm, prctl_map.exe_fd);
+ down_read(&mm->mmap_sem);
if (error)
goto out;
@@ -1909,12 +1922,8 @@ static int prctl_set_mm(int opt, unsigned long addr,
if (!capable(CAP_SYS_RESOURCE))
return -EPERM;
- if (opt == PR_SET_MM_EXE_FILE) {
- down_write(&mm->mmap_sem);
- error = prctl_set_mm_exe_file_locked(mm, (unsigned int)addr);
- up_write(&mm->mmap_sem);
- return error;
- }
+ if (opt == PR_SET_MM_EXE_FILE)
+ return prctl_set_mm_exe_file(mm, (unsigned int)addr);
if (addr >= TASK_SIZE || addr < mmap_min_addr)
return -EINVAL;