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Fix a use after free bug in kernel->userspace relay file support
Coverity spotted what looks like a real possible case of using a variable after it has been freed. The problem is in kernel/relay.c::relay_open_buf() If the code hits "goto free_buf;" it ends up in this code : free_buf: relay_destroy_buf(buf); <--- calls kfree() on 'buf'. free_name: kfree(tmpname); end: return buf; <-- use after free of 'buf'. I read through the callers and they all handle a NULL return from this function as an error (and hitting the 'free_buf' label only happens on failure to chan->cb->create_buf_file(), so that looks like a clear error to me). The patch simply sets 'buf' to NULL after the call to relay_destroy_buf(buf); - as far as I can see that should take care of the problem. The patch also corrects a reference to a documentation file while I was at it. Note from Mathieu: the documentation reference change should have been done in a separate patch, but I guess no one will really care. Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com> Acked-by: "David J. Wilder" <wilder@us.ibm.com> Tested-by: "David J. Wilder" <wilder@us.ibm.com> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Cc: Tom Zanussi <zanussi@us.ibm.com> Cc: Karim Yaghmour <karim@opersys.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -1,7 +1,7 @@
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/*
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* Public API and common code for kernel->userspace relay file support.
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*
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* See Documentation/filesystems/relayfs.txt for an overview of relayfs.
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* See Documentation/filesystems/relay.txt for an overview.
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*
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* Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
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* Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com)
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@ -426,6 +426,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
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free_buf:
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relay_destroy_buf(buf);
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buf = NULL;
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free_name:
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kfree(tmpname);
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end:
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