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


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