[PATCH bpf-next v3 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

[Eugene Syromiatnikov <esyr@redhat.com>]

Check that size would not overflow before calculation (and return
-EOVERFLOW if it will), to prevent potential out-of-bounds write
with the following copy_from_user.  Use kvmalloc_array
in copy_user_syms to prevent out-of-bounds write into syms
(and especially buf) as well.

Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
Cc: <stable@vger.kernel.org> # 5.18
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
 kernel/trace/bpf_trace.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 7141ca8..9c041be 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2261,11 +2261,11 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
 	int err = -ENOMEM;
 	unsigned int i;
 
-	syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
+	syms = kvmalloc_array(cnt, sizeof(*syms), GFP_KERNEL);
 	if (!syms)
 		goto error;
 
-	buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
+	buf = kvmalloc_array(cnt, KSYM_NAME_LEN, GFP_KERNEL);
 	if (!buf)
 		goto error;
 
@@ -2461,7 +2461,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	if (!cnt)
 		return -EINVAL;
 
-	size = cnt * sizeof(*addrs);
+	if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
+		return -EOVERFLOW;
 	addrs = kvmalloc(size, GFP_KERNEL);
 	if (!addrs)
 		return -ENOMEM;
-- 
2.1.4