mm_for_maps: shift down_read(mmap_sem) to the caller

commit 00f89d218523b9bf6b522349c039d5ac80aa536d upstream.

mm_for_maps() takes ->mmap_sem after security checks, this looks
strange and obfuscates the locking rules. Move this lock to its
single caller, m_start().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 500b7af91b5c0b029cb30a76ba51f3ee19a2e7f3..76f9ffc6bdde53056b20ebc59602a46d8ff4b7d1 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -240,9 +240,8 @@ static int check_mem_permission(struct task_struct *task)
 struct mm_struct *mm_for_maps(struct task_struct *task)
 {
        struct mm_struct *mm = get_task_mm(task);
-       if (!mm)
-               return NULL;
-       if (mm != current->mm) {
+
+       if (mm && mm != current->mm) {
                /*
                 * task->mm can be changed before security check,
                 * in that case we must notice the change after.
@@ -250,10 +249,9 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
                if (!ptrace_may_access(task, PTRACE_MODE_READ) ||
                    mm != task->mm) {
                        mmput(mm);
-                       return NULL;
+                       mm = NULL;
                }
        }
-       down_read(&mm->mmap_sem);
        return mm;
 }
 

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index c7f64a9f11b1087f174c858655509c5d4c90cbfd..d8be92a171f3285e08b3eb8f6b441de260d2d9a5 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -119,6 +119,7 @@ static void *m_start(struct seq_file *m, loff_t *pos)
        mm = mm_for_maps(priv->task);
        if (!mm)
                return NULL;
+       down_read(&mm->mmap_sem);
 
        tail_vma = get_gate_vma(priv->task);
        priv->tail_vma = tail_vma;

diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 5d84e7121df819cd0d9eb8b9bd54973edf5b77ed..737d219c7993ce0ec7d05ef2d1378426daa9d0a1 100644 (file)
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -137,6 +137,7 @@ static void *m_start(struct seq_file *m, loff_t *pos)
                priv->task = NULL;
                return NULL;
        }
+       down_read(&mm->mmap_sem);
 
        /* start from the Nth VMA */
        for (vml = mm->context.vmlist; vml; vml = vml->next)