1335075 - RTCCertificate.cpp: output truncated before the last format character

Status: RESOLVED FIXED

(Core :: WebRTC, defect, P3)

Description

[Sylvestre Ledru [:Sylvestre]]

0:25.93 /root/firefox-gcc-last/dom/media/webrtc/RTCCertificate.cpp: In member function 'nsresult mozilla::dom::GenerateRTCCertificateTask::GenerateCertificate()':
 0:25.93 /root/firefox-gcc-last/dom/media/webrtc/RTCCertificate.cpp:85:12: error: output truncated before the last format character [-Werror=format-truncation=]
 0:25.93    nsresult GenerateCertificate()
 0:25.93             ^~~~~~~~~~~~~~~~~~~
 0:25.93 /root/firefox-gcc-last/dom/media/webrtc/RTCCertificate.cpp:78:15: note: format output 3 bytes into a destination of size 2
 0:25.93        snprintf(&buf[i * 2 + 3], 2, "%.2x", randomName[i]);
 0:25.93        ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Should be 3:
uint8 to hexa is 2 bytes + terminating nul

Comment 1

[Sylvestre Ledru [:Sylvestre]]

Attachment: Bug 1335075 - RTCCertificate.cpp: output truncated before the last format character

Review commit: https://reviewboard.mozilla.org/r/108284/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/108284/

Comment 2

[Randell Jesup [:jesup] (needinfo me)]

Comment on attachment 8831730 [details]
Bug 1335075 - RTCCertificate.cpp: output truncated before the last format character

https://reviewboard.mozilla.org/r/108284/#review109440

This will result in a bunch of unneeded nul-byte writes... IIRC snprintf truncates the output (thus the warning), but the code follows the loop with adding a trailing nul.  I'd prefer to change it to something else that also avoids the writes, or suppress the warning.  The code is correct as-is. Can we leave it, or suppress?
In practice, the writes will tend to get whomped in the cache before hitting memory, but still...

Comment 3

[Sylvestre Ledru [:Sylvestre]]

Randell, what about?

-      snprintf(&buf[i * 2 + 3], 2, "%.2x", randomName[i]);
+      sprintf(&buf[i * 2 + 3], "%.2x", randomName[i]);

Comment 4

[Randell Jesup [:jesup] (needinfo me)]

(In reply to Sylvestre Ledru [:sylvestre] from comment #3)
> Randell, what about?
> 
> -      snprintf(&buf[i * 2 + 3], 2, "%.2x", randomName[i]);
> +      sprintf(&buf[i * 2 + 3], "%.2x", randomName[i]);

If you did that, you could remove the extra nul write at the end... but it basically has the same problem, writing many nuls and then overwriting them.  land the patch you originally gave; snprintf to make hex values isn't efficient in the first place, so it's not a big deal.

Comment 5

[Sylvestre Ledru [:Sylvestre]]

thanks!

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/369da2e22d43
RTCCertificate.cpp: output truncated before the last format character r=jesup

Comment 8

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/369da2e22d43