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authorJann Horn <jannh@google.com>2019-07-04 17:32:23 +0200
committerBen Hutchings <ben@decadent.org.uk>2019-07-23 19:43:17 +0100
commitd5d5bd909a4f03f132ee3fd3f6f0568c8344eee5 (patch)
parentcf2df8f10789ca4ad27ad0217332c2bfe6fe4c26 (diff)
ptrace: Fix ->ptracer_cred handling for PTRACE_TRACEME
commit 6994eefb0053799d2e07cd140df6c2ea106c41ee upstream. Fix two issues: When called for PTRACE_TRACEME, ptrace_link() would obtain an RCU reference to the parent's objective credentials, then give that pointer to get_cred(). However, the object lifetime rules for things like struct cred do not permit unconditionally turning an RCU reference into a stable reference. PTRACE_TRACEME records the parent's credentials as if the parent was acting as the subject, but that's not the case. If a malicious unprivileged child uses PTRACE_TRACEME and the parent is privileged, and at a later point, the parent process becomes attacker-controlled (because it drops privileges and calls execve()), the attacker ends up with control over two processes with a privileged ptrace relationship, which can be abused to ptrace a suid binary and obtain root privileges. Fix both of these by always recording the credentials of the process that is requesting the creation of the ptrace relationship: current_cred() can't change under us, and current is the proper subject for access control. This change is theoretically userspace-visible, but I am not aware of any code that it will actually break. Fixes: 64b875f7ac8a ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP") Signed-off-by: Jann Horn <jannh@google.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
1 files changed, 1 insertions, 3 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 694e650e962d..22beef3e2160 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -80,9 +80,7 @@ void __ptrace_link(struct task_struct *child, struct task_struct *new_parent,
static void ptrace_link(struct task_struct *child, struct task_struct *new_parent)
- rcu_read_lock();
- __ptrace_link(child, new_parent, __task_cred(new_parent));
- rcu_read_unlock();
+ __ptrace_link(child, new_parent, current_cred());