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Subject[PATCH] procfs mem permission cleanup
Date
This cleans up the permission checks done for /proc/PID/mem i/o calls.
It puts all the logic in a new function, check_mem_permission().

The old code repeated the (!MAY_PTRACE(task) || !ptrace_may_attach(task))
magical expression multiple times. The new function does all that work
in one place, with clear comments.

The old code called security_ptrace() twice on successful checks,
once in MAY_PTRACE() and once in __ptrace_may_attach(). Now it's
only called once, and only if all other checks have succeeded.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
fs/proc/base.c | 38 +++++++++++++++++++++++++++++---------
1 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 81d7d14..299ad71 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -195,12 +195,32 @@ static int proc_root_link(struct inode *inode, struct path *path)
return result;
}

-#define MAY_PTRACE(task) \
- (task == current || \
- (task->parent == current && \
- (task->ptrace & PT_PTRACED) && \
- (task_is_stopped_or_traced(task)) && \
- security_ptrace(current,task) == 0))
+/*
+ * Return zero if current may access user memory in @task, -error if not.
+ */
+static int check_mem_permission(struct task_struct *task)
+{
+ /*
+ * A task can always look at itself, in case it chooses
+ * to use system calls instead of load instructions.
+ */
+ if (task == current)
+ return 0;
+
+ /*
+ * If current is actively ptrace'ing, and would also be
+ * permitted to freshly attach with ptrace now, permit it.
+ */
+ if (task->parent == current && (task->ptrace & PT_PTRACED) &&
+ task_is_stopped_or_traced(task) &&
+ ptrace_may_attach(task))
+ return 0;
+
+ /*
+ * Noone else is allowed.
+ */
+ return -EPERM;
+}

struct mm_struct *mm_for_maps(struct task_struct *task)
{
@@ -715,7 +735,7 @@ static ssize_t mem_read(struct file * file, char __user * buf,
if (!task)
goto out_no_task;

- if (!MAY_PTRACE(task) || !ptrace_may_attach(task))
+ if (check_mem_permission(task))
goto out;

ret = -ENOMEM;
@@ -741,7 +761,7 @@ static ssize_t mem_read(struct file * file, char __user * buf,

this_len = (count > PAGE_SIZE) ? PAGE_SIZE : count;
retval = access_process_vm(task, src, page, this_len, 0);
- if (!retval || !MAY_PTRACE(task) || !ptrace_may_attach(task)) {
+ if (!retval || check_mem_permission(task)) {
if (!ret)
ret = -EIO;
break;
@@ -785,7 +805,7 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
if (!task)
goto out_no_task;

- if (!MAY_PTRACE(task) || !ptrace_may_attach(task))
+ if (check_mem_permission(task))
goto out;

copied = -ENOMEM;

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