[PATCH bpf-next v4 1/2] bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules

[Viktor Malik <vmalik@xxxxxxxxxx>]

When attaching fentry/fexit/fmod_ret/lsm to a function located in a
module without specifying the target program, the verifier tries to find
the address to attach to in kallsyms. This is always done by searching
the entire kallsyms, not respecting the module in which the function is
located.

This approach causes an incorrect attachment address to be computed if
the function to attach to is shadowed by a function of the same name
located earlier in kallsyms.

Since the attachment must contain the BTF of the program to attach to,
we may extract the module from it and search for the function address in
the module.

Signed-off-by: Viktor Malik <vmalik@xxxxxxxxxx>
---
 kernel/bpf/verifier.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a5255a0dcbb6..d646c5263bc5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -24,6 +24,7 @@
 #include <linux/bpf_lsm.h>
 #include <linux/btf_ids.h>
 #include <linux/poison.h>
+#include "../module/internal.h"
 
 #include "disasm.h"
 
@@ -16478,6 +16479,7 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
 	const char *tname;
 	struct btf *btf;
 	long addr = 0;
+	struct module *mod;
 
 	if (!btf_id) {
 		bpf_log(log, "Tracing programs must provide btf_id\n");
@@ -16645,7 +16647,19 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
 			else
 				addr = (long) tgt_prog->aux->func[subprog]->bpf_func;
 		} else {
-			addr = kallsyms_lookup_name(tname);
+			if (btf_is_module(btf)) {
+				preempt_disable();
+				mod = btf_try_get_module(btf);
+				if (mod) {
+					addr = find_kallsyms_symbol_value(mod, tname);
+					module_put(mod);
+				} else {
+					addr = 0;
+				}
+				preempt_enable();
+			} else {
+				addr = kallsyms_lookup_name(tname);
+			}
 			if (!addr) {
 				bpf_log(log,
 					"The address of function %s cannot be found\n",
-- 
2.38.1