[PATCH bpf v3 1/2] 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.  Add the same check
to kprobe_multi_resolve_syms in case it will be called from elsewhere
in the future.

Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
 kernel/trace/bpf_trace.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d8553f4..212faa4 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2352,13 +2352,15 @@ static int
 kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
 			  unsigned long *addrs)
 {
-	unsigned long addr, size;
+	unsigned long addr, sym_size;
+	u32 size;
 	const char __user **syms;
 	int err = -ENOMEM;
 	unsigned int i;
 	char *func;
 
-	size = cnt * sizeof(*syms);
+	if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size))
+		return -EOVERFLOW;
 	syms = kvzalloc(size, GFP_KERNEL);
 	if (!syms)
 		return -ENOMEM;
@@ -2382,9 +2384,9 @@ kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
 		addr = kallsyms_lookup_name(func);
 		if (!addr)
 			goto error;
-		if (!kallsyms_lookup_size_offset(addr, &size, NULL))
+		if (!kallsyms_lookup_size_offset(addr, &sym_size, NULL))
 			goto error;
-		addr = ftrace_location_range(addr, addr + size - 1);
+		addr = ftrace_location_range(addr, addr + sym_size - 1);
 		if (!addr)
 			goto error;
 		addrs[i] = addr;
@@ -2429,7 +2431,8 @@ 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