[PATCH v4 1/5] pagemap: check permissions and capabilities at open time

Konstantin Khlebnikov
2015-07-14T15:39:37Z

This patch moves permission checks from pagemap_read() into pagemap_open().

Pointer to mm is saved in file->private_data. This reference pins only
mm_struct itself. /proc/*/mem, maps, smaps already work in the same way.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Link: http://lkml.kernel.org/r/CA+55aFyKpWrt_Ajzh1rzp_GcwZ4=6Y=kOv8hBz172CFJp6L8Tg@mail.gmail.com
---
fs/proc/task_mmu.c | 48 ++++++++++++++++++++++++++++--------------------
1 file changed, 28 insertions(+), 20 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index ca1e091881d4..270bf7cbc8a5 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1227,40 +1227,33 @@ static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask,
static ssize_t pagemap_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
- struct task_struct *task = get_proc_task(file_inode(file));
- struct mm_struct *mm;
+ struct mm_struct *mm = file->private_data;
struct pagemapread pm;
- int ret = -ESRCH;
struct mm_walk pagemap_walk = {};
unsigned long src;
unsigned long svpfn;
unsigned long start_vaddr;
unsigned long end_vaddr;
- int copied = 0;
+ int ret = 0, copied = 0;

- if (!task)
+ if (!mm || !atomic_inc_not_zero(&mm->mm_users))
goto out;

ret = -EINVAL;
/* file position must be aligned */
if ((*ppos % PM_ENTRY_BYTES) || (count % PM_ENTRY_BYTES))
- goto out_task;
+ goto out_mm;

ret = 0;
if (!count)
- goto out_task;
+ goto out_mm;

pm.v2 = soft_dirty_cleared;
pm.len = (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
pm.buffer = kmalloc(pm.len * PM_ENTRY_BYTES, GFP_TEMPORARY);
ret = -ENOMEM;
if (!pm.buffer)
- goto out_task;
-
- mm = mm_access(task, PTRACE_MODE_READ);
- ret = PTR_ERR(mm);
- if (!mm || IS_ERR(mm))
- goto out_free;
+ goto out_mm;

pagemap_walk.pmd_entry = pagemap_pte_range;
pagemap_walk.pte_hole = pagemap_pte_hole;
@@ -1273,10 +1266,10 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
src = *ppos;
svpfn = src / PM_ENTRY_BYTES;
start_vaddr = svpfn << PAGE_SHIFT;
- end_vaddr = TASK_SIZE_OF(task);
+ end_vaddr = mm->task_size;

/* watch out for wraparound */
- if (svpfn > TASK_SIZE_OF(task) >> PAGE_SHIFT)
+ if (svpfn > mm->task_size >> PAGE_SHIFT)
start_vaddr = end_vaddr;

/*
@@ -1303,7 +1296,7 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
len = min(count, PM_ENTRY_BYTES * pm.pos);
if (copy_to_user(buf, pm.buffer, len)) {
ret = -EFAULT;
- goto out_mm;
+ goto out_free;
}
copied += len;
buf += len;
@@ -1313,24 +1306,38 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
if (!ret || ret == PM_END_OF_BUFFER)
ret = copied;

-out_mm:
- mmput(mm);
out_free:
kfree(pm.buffer);
-out_task:
- put_task_struct(task);
+out_mm:
+ mmput(mm);
out:
return ret;
}

static int pagemap_open(struct inode *inode, struct file *file)
{
+ struct mm_struct *mm;
+
/* do not disclose physical addresses: attack vector */
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
pr_warn_once("Bits 55-60 of /proc/PID/pagemap entries are about "
"to stop being page-shift some time soon. See the "
"linux/Documentation/vm/pagemap.txt for details.\n");
+
+ mm = proc_mem_open(inode, PTRACE_MODE_READ);
+ if (IS_ERR(mm))
+ return PTR_ERR(mm);
+ file->private_data = mm;
+ return 0;
+}
+
+static int pagemap_release(struct inode *inode, struct file *file)
+{
+ struct mm_struct *mm = file->private_data;
+
+ if (mm)
+ mmdrop(mm);
return 0;
}

@@ -1338,6 +1345,7 @@ const struct file_operations proc_pagemap_operations = {
.llseek = mem_lseek, /* borrow this */
.read = pagemap_read,
.open = pagemap_open,
+ .release = pagemap_release,
};
#endif /* CONFIG_PROC_PAGE_MONITOR */