Patchwork scm: fix scm_fp_list->list initialization made in wrong place

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Submitter Pavel Emelyanov
Date Nov. 14, 2008, 2:32 p.m.
Message ID <491D8C1A.5060003@openvz.org>
Download mbox | patch
Permalink /patch/8766/
State Accepted
Delegated to: David Miller
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Comments

Pavel Emelyanov - Nov. 14, 2008, 2:32 p.m.
This is the next page of the scm recursion story (the commit 
f8d570a4 net: Fix recursive descent in __scm_destroy()).

In function scm_fp_dup(), the INIT_LIST_HEAD(&fpl->list) of newly
created fpl is done *before* the subsequent memcpy from the old 
structure and thus the freshly initialized list is overwritten.

But that's OK, since this initialization is not required at all,
since the fpl->list is list_add-ed at the destruction time in any
case (and is unused in other code), so I propose to drop both
initializations, rather than moving it after the memcpy.

Please, correct me if I miss something significant.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

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David Miller - Nov. 14, 2008, 10:52 p.m.
From: Pavel Emelyanov <xemul@openvz.org>
Date: Fri, 14 Nov 2008 17:32:58 +0300

> This is the next page of the scm recursion story (the commit 
> f8d570a4 net: Fix recursive descent in __scm_destroy()).
> 
> In function scm_fp_dup(), the INIT_LIST_HEAD(&fpl->list) of newly
> created fpl is done *before* the subsequent memcpy from the old 
> structure and thus the freshly initialized list is overwritten.
> 
> But that's OK, since this initialization is not required at all,
> since the fpl->list is list_add-ed at the destruction time in any
> case (and is unused in other code), so I propose to drop both
> initializations, rather than moving it after the memcpy.
> 
> Please, correct me if I miss something significant.
> 
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

Yep, this is totally correct.

Linus even noticed this in my original patch but kept them there
because they seemed harmless to him.

Patch applied to net-2.6, thanks!
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Patch

diff --git a/net/core/scm.c b/net/core/scm.c
index ab242cc..b12303d 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -75,7 +75,6 @@  static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
 		if (!fpl)
 			return -ENOMEM;
 		*fplp = fpl;
-		INIT_LIST_HEAD(&fpl->list);
 		fpl->count = 0;
 	}
 	fpp = &fpl->fp[fpl->count];
@@ -301,7 +300,6 @@  struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 
 	new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
 	if (new_fpl) {
-		INIT_LIST_HEAD(&new_fpl->list);
 		for (i=fpl->count-1; i>=0; i--)
 			get_file(fpl->fp[i]);
 		memcpy(new_fpl, fpl, sizeof(*fpl));