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line-log.c: prevent crash during union of too many ranges

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The existing implementation of range_set_union does not correctly
reallocate memory, leading to a heap overflow when it attempts to union
more than 24 separate line ranges.

For struct range_set *out to grow correctly it must have out->nr set to
the current size of the buffer when it is passed to range_set_grow.
However, the existing implementation of range_set_union only updates
out->nr at the end of the function, meaning that it is always zero
before this. This results in range_set_grow never growing the buffer, as
well as some of the union logic itself being incorrect as !out->nr is
always true.

The reason why 24 is the limit is that the first allocation of size 1
ends up allocating a buffer of size 24 (due to the call to alloc_nr in
ALLOC_GROW). This goes some way to explain why this hasn't been
caught before.

Fix the problem by correctly updating out->nr after reallocating the
range_set. As this results in out->nr containing the same value as the
variable o, replace o with out->nr as well.

Finally, add a new test to help prevent the problem reoccurring in the
future. Thanks to Vegard Nossum for writing the test.

Signed-off-by: Allan Xavier <allan.x.xavier@oracle.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Allan Xavier 2017-03-02 17:29:02 +00:00 committed by Junio C Hamano
parent c3808ca698
commit aaae0bf787
2 changed files with 17 additions and 8 deletions
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15
line-log.c
View file

@ -144,7 +144,7 @@ void sort_and_merge_range_set(struct range_set *rs)
static void range_set_union(struct range_set *out,
struct range_set *a, struct range_set *b)
{
int i = 0, j = 0, o = 0;
int i = 0, j = 0;
struct range *ra = a->ranges;
struct range *rb = b->ranges;
/* cannot make an alias of out->ranges: it may change during grow */
@ -167,16 +167,15 @@ static void range_set_union(struct range_set *out,
new = &rb[j++];
if (new->start == new->end)
; /* empty range */
else if (!o || out->ranges[o-1].end < new->start) {
else if (!out->nr || out->ranges[out->nr-1].end < new->start) {
range_set_grow(out, 1);
out->ranges[o].start = new->start;
out->ranges[o].end = new->end;
o++;
} else if (out->ranges[o-1].end < new->end) {
out->ranges[o-1].end = new->end;
out->ranges[out->nr].start = new->start;
out->ranges[out->nr].end = new->end;
out->nr++;
} else if (out->ranges[out->nr-1].end < new->end) {
out->ranges[out->nr-1].end = new->end;
}
}
out->nr = o;
}
/*

10
t/t4211-line-log.sh
View file

@ -106,4 +106,14 @@ test_expect_success '-L with --output' '
test_line_count = 70 log
'
test_expect_success 'range_set_union' '
test_seq 500 > c.c &&
git add c.c &&
git commit -m "many lines" &&
test_seq 1000 > c.c &&
git add c.c &&
git commit -m "modify many lines" &&
git log $(for x in $(test_seq 200); do echo -L $((2*x)),+1:c.c; done)
'
test_done