[PATCH AUTOSEL 4.20 15/81] bpftool: Fix prog dump by tag

From: Sasha Levin
Date: Thu Feb 28 2019 - 10:08:45 EST

From: Jiri Olsa <jolsa@xxxxxxxxxx>

[ Upstream commit 752bcf80f5549c9901b2e8bc77b2138de55b1026 ]

Lance reported an issue with bpftool not being able to
dump program if there are more programs loaded and you
want to dump any but the first program, like:

# bpftool prog
28: kprobe name trace_req_start tag 1dfc28ba8b3dd597 gpl
loaded_at 2019-01-18T17:02:40+1100 uid 0
xlated 112B jited 109B memlock 4096B map_ids 13
29: kprobe name trace_req_compl tag 5b6a5ecc6030a683 gpl
loaded_at 2019-01-18T17:02:40+1100 uid 0
xlated 928B jited 575B memlock 4096B map_ids 13,14
# bpftool prog dum jited tag 1dfc28ba8b3dd597
0: push %rbp
1: mov %rsp,%rbp

# bpftool prog dum jited tag 5b6a5ecc6030a683
Error: can't get prog info (29): Bad address

The problem is in the prog_fd_by_tag function not cleaning
the struct bpf_prog_info before another request, so the
previous program length is still in there and kernel assumes
it needs to dump the program, which fails because there's no
user pointer set.

Moving the struct bpf_prog_info declaration into the loop,
so it gets cleaned before each query.

Fixes: 71bb428fe2c1 ("tools: bpf: add bpftool")
Reported-by: Lance Digby <ldigby@xxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Reviewed-by: Quentin Monnet <quentin.monnet@xxxxxxxxxxxxx>
Acked-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
tools/bpf/bpftool/prog.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index 69b01a6158bdd..91b9de5f4e17e 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -130,13 +130,14 @@ static void print_boot_time(__u64 nsecs, char *buf, unsigned int size)

static int prog_fd_by_tag(unsigned char *tag)
- struct bpf_prog_info info = {};
- __u32 len = sizeof(info);
unsigned int id = 0;
int err;
int fd;

while (true) {
+ struct bpf_prog_info info = {};
+ __u32 len = sizeof(info);
err = bpf_prog_get_next_id(id, &id);
if (err) {
p_err("%s", strerror(errno));