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Re: [PATCH v2] xfsprogs: fix potential memory leak in verify_set_primary

To: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH v2] xfsprogs: fix potential memory leak in verify_set_primary_sb()
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Wed, 25 Sep 2013 09:28:43 -0500
Cc: Mark Tinguely <tinguely@xxxxxxx>, Chandra Seetharaman <sekharan@xxxxxxxxxx>, xfsprogs <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1380094327.2526.5.camel@ThinkPad-T5421>
References: <1379829679.4089.2.camel@ThinkPad-T5421> <5241E125.7010902@xxxxxxx> <1380094327.2526.5.camel@ThinkPad-T5421>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130801 Thunderbird/17.0.8
On 9/25/13 2:32 AM, Li Zhong wrote:
> This patch tries to fix CID 997012, 997013 and 997014 reported by Coverity 
> scan,
> as suggested by sekharan.
> 
> v2: as Mark pointed out, out in the for loop before also needs list to
> be freed. Also remove out lable as it is not referenced any more.

Fix itself looks good, thanks!  Love to see the scan numbers change
for the better.  ;)

Nitpicks, though: Patch changelogs usually goes below the "---" so
the history of trial and error isn't in the commit log.  Not that big
a deal, it's just convention as mentioned in the kernel SubmittingPatches
doc:

> The "---" marker line serves the essential purpose of marking for patch
> handling tools where the changelog message ends.
> 
> One good use for the additional comments after the "---" marker is for
> a diffstat, to show what files have changed, and the number of
> inserted and deleted lines per file.  A diffstat is especially useful
> on bigger patches.  Other comments relevant only to the moment or the
> maintainer, not suitable for the permanent changelog, should also go
> here.  A good example of such comments might be "patch changelogs"
> which describe what has changed between the v1 and v2 version of the
> patch.


And since we're on the topic of commit messages lately, this one could
be improved too I think.

"CID 997012" won't mean anything to a reader in the future.  It'd be
better to describe what you're fixing on its own terms.  Something like:

===
If verify_set_primary_sb() completes the secondary sb scanning loop with
too few valid secondaries found (num_ok < num_sbs / 2), it will immediately
return without freeing any of the previously allocated memory (variables 
sb, checked, and any items on the geo list).  This was reported by
the Coverity scanner as CID 997012, 997013 and 997014.

Fix this by using the out_free_list: goto target for this error case.

Earlier, if get_sb() fails in the secondary scan loop, it goes to
the out: target which does not free any items on the geo list.   Fix
this by using the out_free_list: target as well, and remove the now-unused
out: target.
===

On the one hand, the fix isn't that complicated so it probably speaks for
itself.  But it was complicated enough to warrant discussion & V2 on the list,
so probably worth including that detail in the final changelog.


Also, in looking at this, I wonder if there's another minor buglet.

in phase1.c, we turn the return value from verify_set_primary_sb() into
an error string via err_string(rval).  This handles the various
error returns such as XR_INSUFF_SEC_SB, XR_EOF, etc.  But in the 2nd
case above (get_sb failure), it simply returns "1" which will be interpreted
as XR_BAD_MAGIC ("bad magic number").

get_sb() actually returns several XR_* values, so we should probably capture
it and use that return value?  That'd be a different patch though.

I guess the comment for verify_set_primary_sb() would be changed
then too, now it says:

 * returns 1 if bad, 0 if ok

but today we actually return 0, 1, or XR_INSUFF_SEC_SB.

Not that big a deal, but it seems like the error returns, their handling,
and associated comments aren't quite consistent.

Thanks,
-Eric


> Signed-off-by: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
> ---
>  repair/sb.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/repair/sb.c b/repair/sb.c
> index aa550e3..d34d7a2 100644
> --- a/repair/sb.c
> +++ b/repair/sb.c
> @@ -733,7 +733,7 @@ verify_set_primary_sb(xfs_sb_t            *rsb,
>  
>                       if (get_sb(sb, off, size, agno) == XR_EOF)  {
>                               retval = 1;
> -                             goto out;
> +                             goto out_free_list;
>                       }
>  
>                       if (verify_sb(sb, 0) == XR_OK)  {
> @@ -756,8 +756,10 @@ verify_set_primary_sb(xfs_sb_t           *rsb,
>       /*
>        * see if we have enough superblocks to bother with
>        */
> -     if (num_ok < num_sbs / 2)
> -             return(XR_INSUFF_SEC_SB);
> +     if (num_ok < num_sbs / 2) {
> +             retval = XR_INSUFF_SEC_SB;
> +             goto out_free_list;
> +     }
>  
>       current = get_best_geo(list);
>  
> @@ -841,7 +843,6 @@ verify_set_primary_sb(xfs_sb_t            *rsb,
>  
>  out_free_list:
>       free_geo(list);
> -out:
>       free(sb);
>       free(checked);
>       return(retval);
> 

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