Re: KMSAN: uninit-value in af_alg_free_areq_sgls

[Dmitry Vyukov <dvyukov@google.com>]

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On Fri, Jul 6, 2018 at 10:19 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Fri, Jul 6, 2018 at 10:09 AM, syzbot
> <syzbot+9c251bdd09f83b92ba95@syzkaller.appspotmail.com> wrote:
>> Hello,
>>
>> syzbot tried to test the proposed patch but build/boot failed:
>>
>> lost connection to test machine
>
> Looking into this.

Should be fixed now, let's try again:

#syz test: https://github.com/google/kmsan.git master


>> [....] Starting enhanced syslogd: rsyslogd [?25l [?1c 7 [1G[ [32m ok [39;49m
>> 8 [?25h [?0c.
>> [....] Starting periodic command scheduler: cron [?25l [?1c 7 [1G[ [32m ok
>> [39;49m 8 [?25h [?0c.
>> [....] Starting OpenBSD Secure Shell server: sshd[   21.709280] random:
>> sshd: uninitialized urandom read (32 bytes read)
>> [?25l [?1c 7 [1G[ [32m ok  [39;49m 8 [?25h [?0c.
>>
>> Debian GNU/Linux 7 syzkaller ttyS0
>>
>> syzkaller login: [   26.229113] random: sshd: uninitialized urandom read (32
>> bytes read)
>> [   26.532843] random: sshd: uninitialized urandom read (32 bytes read)
>> [   27.787277] random: sshd: uninitialized urandom read (32 bytes read)
>> Warning: Permanently added '10.128.0.2' (ECDSA) to the list of known hosts.
>> [   33.299368] random: sshd: uninitialized urandom read (32 bytes read)
>> flag provided but not defined: -os
>> Usage of ./syz-fuzzer:
>>   -abort_signal int
>>         initial signal to send to executor in error conditions; upgrades to
>> SIGKILL if executor does not exit
>>   -arch string
>>         target arch (default "amd64")
>>   -buffer_size uint
>>         internal buffer size (in bytes) for executor output
>>   -collide
>>         collide syscalls to provoke data races (default true)
>>   -cover
>>         collect feedback signals (coverage)
>>   -debug
>>         debug output from executor
>>   -executor string
>>         path to executor binary (default "./syz-executor")
>>   -ipc string
>>         ipc scheme (pipe/shmem)
>>   -leak
>>         detect memory leaks
>>   -manager string
>>         manager rpc address
>>   -name string
>>         unique name for manager (default "test")
>>   -output string
>>         write programs to none/stdout/dmesg/file (default "stdout")
>>   -pprof string
>>         address to serve pprof profiles
>>   -procs int
>>         number of parallel test processes (default 1)
>>   -sandbox string
>>         sandbox for fuzzing (none/setuid/namespace) (default "none")
>>   -test
>>         enable image testing mode
>>   -threaded
>>         use threaded mode in executor (default true)
>>   -timeout duration
>>         execution timeout
>>   -v int
>>         verbosity
>>
>>
>>
>> Tested on:
>>
>> commit:         9c9df9f275f0 kmsan: remove kmsan_threads_ready
>> git tree:       https://github.com/google/kmsan.git/master
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=b11f4cfb262ee607
>> compiler:       clang version 7.0.0 (trunk 334104)
>> patch:          https://syzkaller.appspot.com/x/patch.diff?x=16a5af84400000
>>
>> --
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>>
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--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -1148,8 +1148,10 @@ int af_alg_get_rsgl(struct sock *sk, struct msghdr *msg, int flags,
 
 		/* make one iovec available as scatterlist */
 		err = af_alg_make_sg(&rsgl->sgl, &msg->msg_iter, seglen);
-		if (err < 0)
+		if (err < 0) {
+			rsgl->sg_num_bytes = 0;
 			return err;
+		}
 
 		/* chain the new scatterlist with previous one */
 		if (areq->last_rsgl)