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Subject[PATCH 2/2] CRED: Guard the setprocattr security hook against ptrace
Date
Guard the setprocattr security hook against ptrace by taking the target task's
cred_guard_mutex around it. The problem is that setprocattr() may otherwise
note the lack of a debugger, and then perform an action on that basis whilst
letting a debugger attach between the two points. Holding cred_guard_mutex
across the test and the action prevents ptrace_attach() from doing that.

Signed-off-by: David Howells <dhowells@redhat.com>
---

fs/proc/base.c | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)


diff --git a/fs/proc/base.c b/fs/proc/base.c
index fb45615..23342e1 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2128,9 +2128,15 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
if (copy_from_user(page, buf, count))
goto out_free;

+ /* Guard against adverse ptrace interaction */
+ length = mutex_lock_interruptible(&task->cred_guard_mutex);
+ if (length < 0)
+ goto out_free;
+
length = security_setprocattr(task,
(char*)file->f_path.dentry->d_name.name,
(void*)page, count);
+ mutex_unlock(&task->cred_guard_mutex);
out_free:
free_page((unsigned long) page);
out:


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