linux-kernel - [PATCH bpf-next v3 3/4] bpf_trace: handle compat in copy_user

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Date:   Tue, 17 May 2022 09:36:36 +0200
From:   Eugene Syromiatnikov <esyr@...hat.com>
To:     Jiri Olsa <jolsa@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next v3 3/4] bpf_trace: handle compat in copy_user_syms

For compat processes, userspace size for syms pointers is different.
Provide compat handling for copying array elements from the user space.

Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
---
 kernel/trace/bpf_trace.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a93a54f..9d3028a 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2253,6 +2253,24 @@ struct user_syms {
 	char *buf;
 };
 
+static inline int get_arr_ptr(unsigned long *p,
+			      unsigned long __user *uaddr, u32 idx)
+{
+	if (unlikely(in_compat_syscall())) {
+		compat_uptr_t __user *compat_uaddr = (compat_uptr_t __user *)uaddr;
+		compat_uptr_t val;
+		int err;
+
+		err = __get_user(val, compat_uaddr + idx);
+		if (!err)
+			*p = val;
+
+		return err;
+	} else {
+		return __get_user(*p, uaddr + idx);
+	}
+}
+
 static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32 cnt)
 {
 	unsigned long __user usymbol;
@@ -2270,7 +2288,7 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
 		goto error;
 
 	for (p = buf, i = 0; i < cnt; i++) {
-		if (__get_user(usymbol, usyms + i)) {
+		if (get_arr_ptr(&usymbol, usyms, i)) {
 			err = -EFAULT;
 			goto error;
 		}
-- 
2.1.4