mm/madvise: replace ptrace attach requirement for process_madvise

stable inclusion
from stable-5.10.24
commit 518f98e390771c9f9bc578e0e6423b9708be2d9c
bugzilla: 51348

--------------------------------

commit 96cfe2c0 upstream.

process_madvise currently requires ptrace attach capability.
PTRACE_MODE_ATTACH gives one process complete control over another
process.  It effectively removes the security boundary between the two
processes (in one direction).  Granting ptrace attach capability even to a
system process is considered dangerous since it creates an attack surface.
This severely limits the usage of this API.

The operations process_madvise can perform do not affect the correctness
of the operation of the target process; they only affect where the data is
physically located (and therefore, how fast it can be accessed).  What we
want is the ability for one process to influence another process in order
to optimize performance across the entire system while leaving the
security boundary intact.

Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and
CAP_SYS_NICE.  PTRACE_MODE_READ to prevent leaking ASLR metadata and
CAP_SYS_NICE for influencing process performance.

Link: https://lkml.kernel.org/r/20210303185807.2160264-1-surenb@google.comSigned-off-by: NSuren Baghdasaryan <surenb@google.com>
Reviewed-by: NKees Cook <keescook@chromium.org>
Acked-by: NMinchan Kim <minchan@kernel.org>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jeff Vander Stoep <jeffv@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tim Murray <timmurray@google.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: <stable@vger.kernel.org>	[5.10+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: N  Weilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

mm/madvise.c

@@ -1202,12 +1202,22 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
 		goto release_task;
 	}
 
-	mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);
+	/* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */
+	mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
 	if (IS_ERR_OR_NULL(mm)) {
 		ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 		goto release_task;
 	}
 
+	/*
+	 * Require CAP_SYS_NICE for influencing process performance. Note that
+	 * only non-destructive hints are currently supported.
+	 */
+	if (!capable(CAP_SYS_NICE)) {
+		ret = -EPERM;
+		goto release_mm;
+	}
+
 	total_len = iov_iter_count(&iter);
 
 	while (iov_iter_count(&iter)) {
@@ -1222,6 +1232,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
 	if (ret == 0)
 		ret = total_len - iov_iter_count(&iter);
 
+release_mm:
 	mmput(mm);
 release_task:
 	put_task_struct(task);