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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: "Jesper Dangaard Brouer" <brouer@redhat.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Andrii Nakryiko" <andriin@fb.com>,
	"Sasha Levin" <sashal@kernel.org>,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	clang-built-linux@googlegroups.com
Subject: [PATCH AUTOSEL 5.4 191/205] samples/bpf: Fix broken xdp_rxq_info due to map order assumptions
Date: Thu, 16 Jan 2020 11:42:46 -0500
Message-ID: <20200116164300.6705-191-sashal@kernel.org> (raw)
In-Reply-To: <20200116164300.6705-1-sashal@kernel.org>

From: Jesper Dangaard Brouer <brouer@redhat.com>

[ Upstream commit edbca120a8cdfa5a5793707e33497aa5185875ca ]

In the days of using bpf_load.c the order in which the 'maps' sections
were defines in BPF side (*_kern.c) file, were used by userspace side
to identify the map via using the map order as an index. In effect the
order-index is created based on the order the maps sections are stored
in the ELF-object file, by the LLVM compiler.

This have also carried over in libbpf via API bpf_map__next(NULL, obj)
to extract maps in the order libbpf parsed the ELF-object file.

When BTF based maps were introduced a new section type ".maps" were
created. I found that the LLVM compiler doesn't create the ".maps"
sections in the order they are defined in the C-file. The order in the
ELF file is based on the order the map pointer is referenced in the code.

This combination of changes lead to xdp_rxq_info mixing up the map
file-descriptors in userspace, resulting in very broken behaviour, but
without warning the user.

This patch fix issue by instead using bpf_object__find_map_by_name()
to find maps via their names. (Note, this is the ELF name, which can
be longer than the name the kernel retains).

Fixes: be5bca44aa6b ("samples: bpf: convert some XDP samples from bpf_load to libbpf")
Fixes: 451d1dc886b5 ("samples: bpf: update map definition to new syntax BTF-defined map")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/157529025128.29832.5953245340679936909.stgit@firesoul
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 samples/bpf/xdp_rxq_info_user.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/samples/bpf/xdp_rxq_info_user.c b/samples/bpf/xdp_rxq_info_user.c
index c7e4e45d824a..b88df17853b8 100644
--- a/samples/bpf/xdp_rxq_info_user.c
+++ b/samples/bpf/xdp_rxq_info_user.c
@@ -489,9 +489,9 @@ int main(int argc, char **argv)
 	if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))
 		return EXIT_FAIL;
 
-	map = bpf_map__next(NULL, obj);
-	stats_global_map = bpf_map__next(map, obj);
-	rx_queue_index_map = bpf_map__next(stats_global_map, obj);
+	map =  bpf_object__find_map_by_name(obj, "config_map");
+	stats_global_map = bpf_object__find_map_by_name(obj, "stats_global_map");
+	rx_queue_index_map = bpf_object__find_map_by_name(obj, "rx_queue_index_map");
 	if (!map || !stats_global_map || !rx_queue_index_map) {
 		printf("finding a map in obj file failed\n");
 		return EXIT_FAIL;
-- 
2.20.1


      parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200116164300.6705-1-sashal@kernel.org>
2020-01-16 16:40 ` [PATCH AUTOSEL 5.4 049/205] net: netsec: Correct dma sync for XDP_TX frames Sasha Levin
2020-01-16 16:40 ` [PATCH AUTOSEL 5.4 077/205] libbpf: Fix compatibility for kernels without need_wakeup Sasha Levin
2020-01-16 16:40 ` [PATCH AUTOSEL 5.4 080/205] libbpf: Don't use kernel-side u32 type in xsk.c Sasha Levin
2020-01-16 16:41 ` [PATCH AUTOSEL 5.4 111/205] libbpf: Fix memory leak/double free issue Sasha Levin
2020-01-16 16:41 ` [PATCH AUTOSEL 5.4 112/205] libbpf: Fix potential overflow issue Sasha Levin
2020-01-16 16:41 ` [PATCH AUTOSEL 5.4 113/205] libbpf: Fix another potential overflow issue in bpf_prog_linfo Sasha Levin
2020-01-16 16:41 ` [PATCH AUTOSEL 5.4 114/205] libbpf: Make btf__resolve_size logic always check size error condition Sasha Levin
2020-01-16 16:42 ` [PATCH AUTOSEL 5.4 155/205] libbpf: Fix call relocation offset calculation bug Sasha Levin
2020-01-16 16:42 ` [PATCH AUTOSEL 5.4 164/205] bpf: skmsg, fix potential psock NULL pointer dereference Sasha Levin
2020-01-16 16:42 ` [PATCH AUTOSEL 5.4 172/205] xdp: Fix cleanup on map free for devmap_hash map type Sasha Levin
2020-01-16 16:42 ` [PATCH AUTOSEL 5.4 179/205] bpf: Support pre-2.25-binutils objcopy for vmlinux BTF Sasha Levin
2020-01-16 16:42 ` [PATCH AUTOSEL 5.4 180/205] libbpf: Fix Makefile' libbpf symbol mismatch diagnostic Sasha Levin
2020-01-16 16:42 ` [PATCH AUTOSEL 5.4 186/205] bpf: Force .BTF section start to zero when dumping from vmlinux Sasha Levin
2020-01-16 16:42 ` Sasha Levin [this message]

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