drivers/vhost/net.c:1080 get_rx_bufs() error: uninitialized symbol 'len'.

From: kernel test robot
Date: Fri Aug 07 2020 - 16:41:46 EST

tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head: 5631c5e0eb9035d92ceb20fcd9cdb7779a3f5cc7
commit: 3f649ab728cda8038259d8f14492fe400fbab911 treewide: Remove uninitialized_var() usage
date: 3 weeks ago
config: x86_64-randconfig-m031-20200807 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>

smatch warnings:
drivers/vhost/net.c:1080 get_rx_bufs() error: uninitialized symbol 'len'.

vim +/len +1080 drivers/vhost/net.c

03088137246065 Jason Wang 2016-03-04 1018
8dd014adfea6f1 David Stevens 2010-07-27 1019 /* This is a multi-buffer version of vhost_get_desc, that works if
8dd014adfea6f1 David Stevens 2010-07-27 1020 * vq has read descriptors only.
8dd014adfea6f1 David Stevens 2010-07-27 1021 * @vq - the relevant virtqueue
8dd014adfea6f1 David Stevens 2010-07-27 1022 * @datalen - data length we'll be reading
8dd014adfea6f1 David Stevens 2010-07-27 1023 * @iovcount - returned count of io vectors we fill
8dd014adfea6f1 David Stevens 2010-07-27 1024 * @log - vhost log
8dd014adfea6f1 David Stevens 2010-07-27 1025 * @log_num - log offset
94249369e99302 Jason Wang 2011-01-17 1026 * @quota - headcount quota, 1 for big buffer
8dd014adfea6f1 David Stevens 2010-07-27 1027 * returns number of buffer heads allocated, negative on error
8dd014adfea6f1 David Stevens 2010-07-27 1028 */
8dd014adfea6f1 David Stevens 2010-07-27 1029 static int get_rx_bufs(struct vhost_virtqueue *vq,
8dd014adfea6f1 David Stevens 2010-07-27 1030 struct vring_used_elem *heads,
8dd014adfea6f1 David Stevens 2010-07-27 1031 int datalen,
8dd014adfea6f1 David Stevens 2010-07-27 1032 unsigned *iovcount,
8dd014adfea6f1 David Stevens 2010-07-27 1033 struct vhost_log *log,
94249369e99302 Jason Wang 2011-01-17 1034 unsigned *log_num,
94249369e99302 Jason Wang 2011-01-17 1035 unsigned int quota)
8dd014adfea6f1 David Stevens 2010-07-27 1036 {
8dd014adfea6f1 David Stevens 2010-07-27 1037 unsigned int out, in;
8dd014adfea6f1 David Stevens 2010-07-27 1038 int seg = 0;
8dd014adfea6f1 David Stevens 2010-07-27 1039 int headcount = 0;
8dd014adfea6f1 David Stevens 2010-07-27 1040 unsigned d;
8dd014adfea6f1 David Stevens 2010-07-27 1041 int r, nlogs = 0;
8b38694a2dc8b1 Michael S. Tsirkin 2014-10-24 1042 /* len is always initialized before use since we are always called with
8b38694a2dc8b1 Michael S. Tsirkin 2014-10-24 1043 * datalen > 0.
8b38694a2dc8b1 Michael S. Tsirkin 2014-10-24 1044 */
3f649ab728cda8 Kees Cook 2020-06-03 1045 u32 len;
8dd014adfea6f1 David Stevens 2010-07-27 1046
94249369e99302 Jason Wang 2011-01-17 1047 while (datalen > 0 && headcount < quota) {
e0e9b406470b8d Jason Wang 2010-09-14 1048 if (unlikely(seg >= UIO_MAXIOV)) {
8dd014adfea6f1 David Stevens 2010-07-27 1049 r = -ENOBUFS;
8dd014adfea6f1 David Stevens 2010-07-27 1050 goto err;
8dd014adfea6f1 David Stevens 2010-07-27 1051 }
47283bef7ed356 Michael S. Tsirkin 2014-06-05 1052 r = vhost_get_vq_desc(vq, vq->iov + seg,
8dd014adfea6f1 David Stevens 2010-07-27 1053 ARRAY_SIZE(vq->iov) - seg, &out,
8dd014adfea6f1 David Stevens 2010-07-27 1054 &in, log, log_num);
a39ee449f96a2c Michael S. Tsirkin 2014-03-27 1055 if (unlikely(r < 0))
a39ee449f96a2c Michael S. Tsirkin 2014-03-27 1056 goto err;
a39ee449f96a2c Michael S. Tsirkin 2014-03-27 1057
a39ee449f96a2c Michael S. Tsirkin 2014-03-27 1058 d = r;
8dd014adfea6f1 David Stevens 2010-07-27 1059 if (d == vq->num) {
8dd014adfea6f1 David Stevens 2010-07-27 1060 r = 0;
8dd014adfea6f1 David Stevens 2010-07-27 1061 goto err;
8dd014adfea6f1 David Stevens 2010-07-27 1062 }
8dd014adfea6f1 David Stevens 2010-07-27 1063 if (unlikely(out || in <= 0)) {
8dd014adfea6f1 David Stevens 2010-07-27 1064 vq_err(vq, "unexpected descriptor format for RX: "
8dd014adfea6f1 David Stevens 2010-07-27 1065 "out %d, in %d\n", out, in);
8dd014adfea6f1 David Stevens 2010-07-27 1066 r = -EINVAL;
8dd014adfea6f1 David Stevens 2010-07-27 1067 goto err;
8dd014adfea6f1 David Stevens 2010-07-27 1068 }
8dd014adfea6f1 David Stevens 2010-07-27 1069 if (unlikely(log)) {
8dd014adfea6f1 David Stevens 2010-07-27 1070 nlogs += *log_num;
8dd014adfea6f1 David Stevens 2010-07-27 1071 log += *log_num;
8dd014adfea6f1 David Stevens 2010-07-27 1072 }
8b38694a2dc8b1 Michael S. Tsirkin 2014-10-24 1073 heads[headcount].id = cpu_to_vhost32(vq, d);
8b38694a2dc8b1 Michael S. Tsirkin 2014-10-24 1074 len = iov_length(vq->iov + seg, in);
8b38694a2dc8b1 Michael S. Tsirkin 2014-10-24 1075 heads[headcount].len = cpu_to_vhost32(vq, len);
8b38694a2dc8b1 Michael S. Tsirkin 2014-10-24 1076 datalen -= len;
8dd014adfea6f1 David Stevens 2010-07-27 1077 ++headcount;
8dd014adfea6f1 David Stevens 2010-07-27 1078 seg += in;
8dd014adfea6f1 David Stevens 2010-07-27 1079 }
99975cc6ada0d5 Michael S. Tsirkin 2015-01-07 @1080 heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
8dd014adfea6f1 David Stevens 2010-07-27 1081 *iovcount = seg;
8dd014adfea6f1 David Stevens 2010-07-27 1082 if (unlikely(log))
8dd014adfea6f1 David Stevens 2010-07-27 1083 *log_num = nlogs;
d8316f3991d207 Michael S. Tsirkin 2014-03-27 1084
d8316f3991d207 Michael S. Tsirkin 2014-03-27 1085 /* Detect overrun */
d8316f3991d207 Michael S. Tsirkin 2014-03-27 1086 if (unlikely(datalen > 0)) {
d8316f3991d207 Michael S. Tsirkin 2014-03-27 1087 r = UIO_MAXIOV + 1;
d8316f3991d207 Michael S. Tsirkin 2014-03-27 1088 goto err;
d8316f3991d207 Michael S. Tsirkin 2014-03-27 1089 }
8dd014adfea6f1 David Stevens 2010-07-27 1090 return headcount;
8dd014adfea6f1 David Stevens 2010-07-27 1091 err:
8dd014adfea6f1 David Stevens 2010-07-27 1092 vhost_discard_vq_desc(vq, headcount);
8dd014adfea6f1 David Stevens 2010-07-27 1093 return r;
8dd014adfea6f1 David Stevens 2010-07-27 1094 }
8dd014adfea6f1 David Stevens 2010-07-27 1095

:::::: The code at line 1080 was first introduced by commit
:::::: 99975cc6ada0d5f2675e83abecae05aba5f437d2 vhost/net: length miscalculation

:::::: TO: Michael S. Tsirkin <mst@xxxxxxxxxx>
:::::: CC: Michael S. Tsirkin <mst@xxxxxxxxxx>

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