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Date: Sun, 10 Oct 2021 17:36:21 +0900 From: asmadeus@...ewreck.org To: syzbot <syzbot+06472778c97ed94af66d@...kaller.appspotmail.com> Cc: davem@...emloft.net, ericvh@...il.com, glider@...gle.com, kuba@...nel.org, linux-kernel@...r.kernel.org, lucho@...kov.net, netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com, v9fs-developer@...ts.sourceforge.net Subject: Re: [syzbot] KMSAN: uninit-value in p9pdu_readf Question for people who know about KMSAN: which of the backtrace or the 'Local variable' message should I trust? syzbot wrote on Sat, Oct 09, 2021 at 10:48:17PM -0700: > ===================================================== > BUG: KMSAN: uninit-value in p9pdu_vreadf net/9p/protocol.c:147 [inline] > BUG: KMSAN: uninit-value in p9pdu_readf+0x46cf/0x4fc0 net/9p/protocol.c:526 > p9pdu_vreadf net/9p/protocol.c:147 [inline] > p9pdu_readf+0x46cf/0x4fc0 net/9p/protocol.c:526 > p9pdu_vreadf net/9p/protocol.c:198 [inline] > p9pdu_readf+0x2080/0x4fc0 net/9p/protocol.c:526 > p9_client_stat+0x2b3/0x710 net/9p/client.c:1724 > v9fs_mount+0xc14/0x12c0 fs/9p/vfs_super.c:170 would be 'len' in p9pdu_vreadf, which has to be set as far as I can understand: > uint16_t len; > > errcode = p9pdu_readf(pdu, proto_version, > "w", &len); > if (errcode) > break; > > *sptr = kmalloc(len + 1, GFP_NOFS); with relevant part of p9pdu_readf being: > case 'w':{ > int16_t *val = va_arg(ap, int16_t *); > __le16 le_val; > if (pdu_read(pdu, &le_val, sizeof(le_val))) { > errcode = -EFAULT; > break; > } > *val = le16_to_cpu(le_val); > } > ... > return errcode; e.g. either len or errcode should be set... But: > Local variable ----ecode@...check_errors created at: > p9_check_errors+0x68/0xb90 net/9p/client.c:506 > p9_client_rpc+0xd90/0x1410 net/9p/client.c:801 is something totally different, p9_client_rpc happens before the p9pdu_readf call in p9_client_stat, and ecode is local to p9_check_errors, I don't see how it could get that far. Note that inspecting p9_check_errors manually, there is a case where ecode is returned (indirectly through err = -ecode) without being initialized, so I will send a patch for that at least, but I have no idea if that is what has been reported and it should be trivial to reproduce so I do not see why syzbot does not have a reproducer -- it retries running the last program that triggered the error before sending the report, right? -- Dominique Martinet | Asmadeus
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