[PATCH 5.2 031/162] libbpf: fix using uninitialized ioctl results

Greg Kroah-Hartman
2019-08-27T08:11:48Z

[ Upstream commit decb705e01a5d325c9876b9674043cde4b54f0db ]

'channels.max_combined' initialized only on ioctl success and
errno is only valid on ioctl failure.

The code doesn't produce any runtime issues, but makes memory
sanitizers angry:

Conditional jump or move depends on uninitialised value(s)
at 0x55C056F: xsk_get_max_queues (xsk.c:336)
by 0x55C05B2: xsk_create_bpf_maps (xsk.c:354)
by 0x55C089F: xsk_setup_xdp_prog (xsk.c:447)
by 0x55C0E57: xsk_socket__create (xsk.c:601)
Uninitialised value was created by a stack allocation
at 0x55C04CD: xsk_get_max_queues (xsk.c:318)

Additionally fixed warning on uninitialized bytes in ioctl arguments:

Syscall param ioctl(SIOCETHTOOL) points to uninitialised byte(s)
at 0x648D45B: ioctl (in /usr/lib64/libc-2.28.so)
by 0x55C0546: xsk_get_max_queues (xsk.c:330)
by 0x55C05B2: xsk_create_bpf_maps (xsk.c:354)
by 0x55C089F: xsk_setup_xdp_prog (xsk.c:447)
by 0x55C0E57: xsk_socket__create (xsk.c:601)
Address 0x1ffefff378 is on thread 1's stack
in frame #1, created by xsk_get_max_queues (xsk.c:318)
Uninitialised value was created by a stack allocation
at 0x55C04CD: xsk_get_max_queues (xsk.c:318)

CC: Magnus Karlsson <magnus.karlsson@intel.com>
Fixes: 1cad07884239 ("libbpf: add support for using AF_XDP sockets")
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/xsk.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index ca272c5b67f47..8e03b65830da0 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -327,15 +327,14 @@ static int xsk_load_xdp_prog(struct xsk_socket *xsk)

static int xsk_get_max_queues(struct xsk_socket *xsk)
{
- struct ethtool_channels channels;
- struct ifreq ifr;
+ struct ethtool_channels channels = { .cmd = ETHTOOL_GCHANNELS };
+ struct ifreq ifr = {};
int fd, err, ret;

fd = socket(AF_INET, SOCK_DGRAM, 0);
if (fd < 0)
return -errno;

- channels.cmd = ETHTOOL_GCHANNELS;
ifr.ifr_data = (void *)&channels;
strncpy(ifr.ifr_name, xsk->ifname, IFNAMSIZ - 1);
ifr.ifr_name[IFNAMSIZ - 1] = '\0';
@@ -345,7 +344,7 @@ static int xsk_get_max_queues(struct xsk_socket *xsk)
goto out;
}

- if (channels.max_combined == 0 || errno == EOPNOTSUPP)
+ if (err || channels.max_combined == 0)
/* If the device says it has no channels, then all traffic
* is sent to a single stream, so max queues = 1.
*/
--
2.20.1