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List: freedesktop-xorg-devel
Subject: Re: [PATCH-V4] xserver: Optional backtrace handler
From: Barry Scott <barry.scott () onelan ! co ! uk>
Date: 2011-10-13 13:28:05
Message-ID: 201110131428.05523.barry.scott () onelan ! co ! uk
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On Wednesday 12 October 2011 18:50:32 Keith Packard wrote:
> On Thu, 6 Oct 2011 13:19:35 +0100, Barry Scott <barry.scott@onelan.co.uk> wrote:
>
> > Is there anything else I need to do to make this patch acceptable
> > for inclusion in Xorg?
>
> Two things:
>
> 1. This option needs to be restricted to root, much like many other
> options in the server (-modulepath, etc). There's a patch in the
> queue which regularizes this, but the xf86 DDX uses:
>
> if ( (geteuid() == 0) && (getuid() != 0) ) {
> FatalError("The '%s' option can only be used by root.\n", argv[i]);
> }
understood, if Xorg is SUID then this is a problem. I can fix that.
>
> 2. I'd love to figure out how to fork at the time of the error; this
> would encourage people to actually use this option regularly.
>
> posix threads makes the usual libc fork() function take the malloc
> mutex across its operations, but I wonder if syscall(SYS_fork) is
> portable enough to be used instead?
Pre forking means that the handler is not dependent on sanity of libc.
The last serious Xorg bug we where trying to fix was a malloc heap corruption
that prevented the "fork on demand" patch from working at all.
Would a fix for the SUID security issue bring this patch up to a suitable
level of usefulness to include in Xorg? Leaving improvements like
fork on demand to a later patch?
Barry
[Attachment #5 (text/html)]
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</style></head><body style=" font-family:'Monospace'; font-size:10pt; \
font-weight:400; font-style:normal;"> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">On Wednesday 12 October 2011 18:50:32 Keith Packard wrote:</p> <p \
style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> On Thu, 6 Oct 2011 \
13:19:35 +0100, Barry Scott <barry.scott@onelan.co.uk> wrote:</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> </p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> > Is there anything \
else I need to do to make this patch acceptable</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">> > for inclusion in Xorg?</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> </p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> Two things:</p> <p \
style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> </p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> 1. This option needs to \
be restricted to root, much like many other</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">> options in the server (-modulepath, \
etc). There's a patch in the</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">> queue which regularizes this, but the xf86 DDX uses:</p> \
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> </p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> if ( (geteuid() == \
0) && (getuid() != 0) ) {</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">> FatalError("The '%s' option can only be used by \
root.\n", argv[i]);</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">> }</p> <p style="-qt-paragraph-type:empty; margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;"><br /></p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">understood, if Xorg is SUID then this is a \
problem. I can fix that.</p> <p style="-qt-paragraph-type:empty; margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;"><br /></p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">> </p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">> 2. I'd love to figure out how to fork at \
the time of the error; this</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">> would encourage people to actually use this option \
regularly.</p> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; \
margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> </p> \
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> posix threads makes \
the usual libc fork() function take the malloc</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">> mutex across its operations, but I \
wonder if syscall(SYS_fork) is</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">> portable enough to be used instead?</p> <p \
style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; \
margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"><br /></p> \
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Pre forking means that the \
handler is not dependent on sanity of libc.</p> <p style=" margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;">The last serious Xorg bug we where trying to fix \
was a malloc heap corruption</p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">that prevented the "fork on demand" patch from working \
at all.</p> <p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;"><br /></p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">Would a fix for the SUID security issue bring this patch up to a \
suitable</p> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; \
margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">level of \
usefulness to include in Xorg? Leaving improvements like</p> <p style=" \
margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; \
-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">fork on demand to a later \
patch?</p> <p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;"><br /></p> <p style=" margin-top:0px; margin-bottom:0px; \
margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; \
-qt-user-state:0;">Barry</p> <p style="-qt-paragraph-type:empty; margin-top:0px; \
margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; \
text-indent:0px; -qt-user-state:0;"><br /></p></body></html>
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