[PATCH] makedumpfile: Fix the variable pfn_needed leaking

[Minfei Huang]

On 11/13/14 at 08:59am, "Zhou, Wenjian/周文剑" wrote:
> On 11/12/2014 08:05 PM, Minfei Huang wrote:
> >On 11/11/14 at 04:54pm, Minfei Huang wrote:
> >>If the page pfn calculated by read_from_splitblock_table is bigger than
> >>pfn_needed, the variable pfn_needed will leak.
> >>
> >>makedumpfile cannot assign the pfn averagely bacause of condition
> >>pfn_needed invalid.
> >>
> >>Signed-off-by: Minfei Huang<mhuang at redhat.com>
> >>---
> >>  makedumpfile.c | 5 +++--
> >>  1 file changed, 3 insertions(+), 2 deletions(-)
> >>
> >>diff --git a/makedumpfile.c b/makedumpfile.c
> >>index 59c4952..8807a90 100644
> >>--- a/makedumpfile.c
> >>+++ b/makedumpfile.c
> >>@@ -8415,7 +8415,7 @@ calculate_end_pfn_by_splitblock(mdf_pfn_t start_pfn,
> >>  		return info->max_mapnr;
> >>
> >>  	mdf_pfn_t end_pfn;
> >>-	long long pfn_needed, offset;
> >>+	long long pfn_needed, offset, per_splitblock_pfn;
> >>  	char *splitblock_value_offset;
> >>
> >>  	pfn_needed = info->num_dumpable / info->num_dumpfile;
> >>@@ -8424,7 +8424,8 @@ calculate_end_pfn_by_splitblock(mdf_pfn_t start_pfn,
> >>  	end_pfn = start_pfn;
> >>
> >>  	while (*cur_splitblock_num<  splitblock->num&&  pfn_needed>  0) {
> >>-		pfn_needed -= read_from_splitblock_table(splitblock_value_offset);
> >>+		per_splitblock_pfn = read_from_splitblock_table(splitblock_value_offset);
> >>+		pfn_needed = pfn_needed<  per_splitblock_pfn ? 0 : pfn_needed - per_splitblock_pfn;
> >Hi, Wenjiang!
> >
> >Sorry, my emall client didnot receive the mail by you, so I reply it
> >here.
> >
> >The split->table is an array to record the pfn count which we need dump.
> >And the memory is divided by the size of info->splitblock_size, the pfn
> >count in each entry will be stored in the entry of split->table.
> >
> >For the purpose, we want to average allocation to the pfns.
> >
> >Here is a case:
> >There are 5 entries in the split->table, and the value is 4, 6, 4, 5, 5.
> >We want to split four pieces to write to four files, and every file will
> >be write 6 pfns.
> >Using the function calculate_end_pfn_by_splitblock, the first file will
> >be assigned all of the pfns(24 pfns).
> >
> >pfn_needed is 6((4+6+4+5+5) / 4) when entry the function.
> >By the end of first loop, the variable pfn_needed = 2(6 - 4).
> >Then move on, the variable will leak to become huge number by the end of
> >second loop, because the return value of function read_from_splitblock_table
> >is 6. The variable pfn_needed is ~4(2 - 6), it is huge.
> >And the loop will break util *cur_splitblock_num == splitblock->num.
> 
> pfn_needed is (long long). If it is -4, won't the loop break?

Oops!

Sorry, I got a mistake. You are right.

> 
> >
> >For above case, it is no sense to use split function, so we should add
> >the condition whether pfn_needed is bigger than the value of
> >read_from_splitblock_table.
> >
> >Thanks
> >Minfei
> >>  		splitblock_value_offset += splitblock->entry_size;
> >>  		++*cur_splitblock_num;
> >>  	}
> >>--
> >>1.8.3.1
> >>
> 
> 
> -- 
> Thanks
> Zhou Wenjian
> 
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