Bug 66332 - drmHandleEvent returns 0 on read() failure
Summary: drmHandleEvent returns 0 on read() failure
Status: RESOLVED MOVED
Alias: None
Product: DRI
Classification: Unclassified
Component: libdrm (show other bugs)
Version: XOrg git
Hardware: All All
: medium normal
Assignee: Default DRI bug account
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Reported: 2013-06-28 16:31 UTC by Michael Gold
Modified: 2019-09-24 17:08 UTC (History)
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Description Michael Gold 2013-06-28 16:31:42 UTC
drmHandleEvent contains this code:
        len = read(fd, buffer, sizeof buffer);
        if (len == 0)
                return 0;
        if (len < sizeof *e)
                return -1;
In the (len < sizeof *e) check, len gets promoted to size_t (which is unsigned); so when len is negative "return -1" won't be executed. Instead, the function continues to the end and returns 0. (The documentation states drmHandleEvent will return -1 if the read fails.)

If there's an error like EBADF, the caller won't detect it and might end up busy-waiting. Rewriting the condition as (len < (int)(sizeof *e)) will fix this.
Comment 1 GitLab Migration User 2019-09-24 17:08:45 UTC
-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been closed from further activity.

You can subscribe and participate further through the new bug through this link to our GitLab instance: https://gitlab.freedesktop.org/mesa/drm/issues/11.


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