libbpf: fix using uninitialized ioctl results

'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 <[email protected]>
Fixes: 1cad07884239 ("libbpf: add support for using AF_XDP sockets")
Signed-off-by: Ilya Maximets <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 5007b5d4fd2c51186a554fb03893dcabd7bef381..e02025bbe36ddb69621461e4e0cfaa8ed1f66a14 100644 (file)
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -317,15 +317,14 @@ 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';
@@ -335,7 +334,7 @@ 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.
                 */