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common_prefix: simplify and fix scanning for prefixes 

common_prefix() scans backwards from the far end of each 'next'
pathspec, starting from 'len', shortening the 'prefix' using 'path' as
a reference.

However, there is a small opportunity for an out-of-bounds access
because len is unconditionally set to prefix-1 after a "direct match"
test failed.  This means that if 'next' is shorter than prefix+2, we
read past it.

Instead of a minimal fix, simplify the loop: scan *forward* over the
'next' entry, remembering the last '/' where it matched the prefix
known so far.  This is far easier to read and also has the advantage
that we only scan over each entry once.

Acked-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Junio C Hamano 2010-06-16 01:02:03 +02:00
parent e0a9110176
commit 42f9852f3c
1 changed files with 13 additions and 13 deletions
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26
dir.c
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@ -31,22 +31,22 @@ static int common_prefix(const char **pathspec)
if (!slash)
return 0;
/*
* The first 'prefix' characters of 'path' are common leading
* path components among the pathspecs we have seen so far,
* including the trailing slash.
*/
prefix = slash - path + 1;
while ((next = *++pathspec) != NULL) {
int len = strlen(next);
if (len >= prefix && !memcmp(path, next, prefix))
int len, last_matching_slash = -1;
for (len = 0; len < prefix && next[len] == path[len]; len++)
if (next[len] == '/')
last_matching_slash = len;
if (len == prefix)
continue;
len = prefix - 1;
for (;;) {
if (!len)
return 0;
if (next[--len] != '/')
continue;
if (memcmp(path, next, len+1))
continue;
prefix = len + 1;
break;
}
if (last_matching_slash < 0)
return 0;
prefix = last_matching_slash + 1;
}
return prefix;
}