linux/kernel
Jann Horn 6994eefb00 ptrace: Fix ->ptracer_cred handling for PTRACE_TRACEME
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: 64b875f7ac ("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>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-07-05 02:00:41 +09:00
..
bpf SPDX update for 5.2-rc6 2019-06-21 09:58:42 -07:00
cgroup treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 451 2019-06-19 17:09:08 +02:00
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livepatch This includes the following fixes: 2019-06-15 07:24:11 -10:00
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trace This includes three fixes: 2019-07-04 10:26:17 +09:00
.gitignore Provide in-kernel headers to make extending kernel easier 2019-04-29 16:48:03 +02:00
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ptrace.c ptrace: Fix ->ptracer_cred handling for PTRACE_TRACEME 2019-07-05 02:00:41 +09:00
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