[PATCH bpf-next] selftests/bpf: trace_helpers.c: Fix segfault

Rong Tao
2023-04-09T08:21:36Z

From: Rong Tao <rongtao@cestc.cn>

When the number of symbols is greater than MAX_SYMS (300000), the access
array struct ksym syms[MAX_SYMS] goes out of bounds, which will result in
a segfault.

Resolve this issue by judging the maximum number and exiting the loop, and
increasing the default size appropriately. (6.2.9 = 329839 below)

$ cat /proc/kallsyms | wc -l
329839

GDB debugging:
$ cd linux/samples/bpf
$ sudo gdb ./sampleip
...
(gdb) r
...
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7e2debf in malloc () from /lib64/libc.so.6
Missing separate debuginfos, use: dnf debuginfo-install
elfutils-libelf-0.189-1.fc37.x86_64 glibc-2.36-9.fc37.x86_64
libzstd-1.5.4-1.fc37.x86_64 zlib-1.2.12-5.fc37.x86_64
(gdb) bt
#0 0x00007ffff7e2debf in malloc () from /lib64/libc.so.6
#1 0x00007ffff7e33f8e in strdup () from /lib64/libc.so.6
#2 0x0000000000403fb0 in load_kallsyms_refresh() from trace_helpers.c
#3 0x00000000004038b2 in main ()

Signed-off-by: Rong Tao <rongtao@cestc.cn>
---
tools/testing/selftests/bpf/trace_helpers.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
index 09a16a77bae4..a9d589c560d2 100644
--- a/tools/testing/selftests/bpf/trace_helpers.c
+++ b/tools/testing/selftests/bpf/trace_helpers.c
@@ -14,7 +14,7 @@

#define DEBUGFS "/sys/kernel/debug/tracing/"

-#define MAX_SYMS 300000
+#define MAX_SYMS 400000
static struct ksym syms[MAX_SYMS];
static int sym_cnt;

@@ -44,7 +44,8 @@ int load_kallsyms_refresh(void)
continue;
syms[i].addr = (long) addr;
syms[i].name = strdup(func);
- i++;
+ if (++i >= MAX_SYMS)
+ break;
}
fclose(f);
sym_cnt = i;
--
2.39.2