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From: | Agustina Arzille |
Subject: | Re: Dangerous use of alloca |
Date: | Tue, 15 Mar 2016 14:57:19 -0300 |
Hello, Samuel. On 2016-03-15 13:31, Samuel Thibault wrote:
Justus Winter, on Tue 15 Mar 2016 14:39:00 +0100, wrote:Quoting Agustina Arzille (2016-03-15 14:11:27) > Hello, everyone. > > I was browsing some gnumach source files, and noticed some dangerous use > of the gcc builtin 'alloca'. In the file kern/bootstrap.c, lines 212 and > 228, we have the following statement: > > memcpy (alloca (len), ...) Good catch. However, alloca is dangerous even if used correctly, and is best be avoided.What do you mean by "dangerous"? I don't think we'll ever get a commandline that does not fit into the stack. Samuel
That's not what I meant. Stack overflow is clearly very unlikely, if notimpossible. What I meant about 'dangerous' is the fact that alloca is being
used inside the list of arguments of a function call, which can lead tosubtle bugs, because alloca modifies the SP register, which is also being
modified by the function arguments being pushed into the stack. See: http://man7.org/linux/man-pages/man3/alloca.3.html , specifically, the section 'BUGS'.
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