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difftool: fix use-after-free
The left and right base directories were pointed to the buf field of two strbufs, which were subject to change. A contrived test case shows the problem where a file with a long enough name to force the strbuf to grow is up-to-date (hence the code path is used where the work tree's version of the file is reused), and then a file that is not up-to-date needs to be written (hence the code path is used where checkout_entry() uses the previously recorded base_dir that is invalid by now). Let's just copy the base_dir strings for use with checkout_entry(), never touch them until the end, and release them then. This is an easily verifiable fix (as opposed to the next-obvious alternative: to re-set base_dir after every loop iteration). This fixes https://github.com/git-for-windows/git/issues/1124 Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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@ -318,6 +318,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
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struct strbuf rpath = STRBUF_INIT, buf = STRBUF_INIT;
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struct strbuf ldir = STRBUF_INIT, rdir = STRBUF_INIT;
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struct strbuf wtdir = STRBUF_INIT;
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char *lbase_dir, *rbase_dir;
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size_t ldir_len, rdir_len, wtdir_len;
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const char *workdir, *tmp;
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int ret = 0, i;
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@ -351,11 +352,11 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
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memset(&wtindex, 0, sizeof(wtindex));
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memset(&lstate, 0, sizeof(lstate));
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lstate.base_dir = ldir.buf;
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lstate.base_dir = lbase_dir = xstrdup(ldir.buf);
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lstate.base_dir_len = ldir.len;
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lstate.force = 1;
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memset(&rstate, 0, sizeof(rstate));
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rstate.base_dir = rdir.buf;
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rstate.base_dir = rbase_dir = xstrdup(rdir.buf);
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rstate.base_dir_len = rdir.len;
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rstate.force = 1;
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@ -625,6 +626,8 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
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exit_cleanup(tmpdir, rc);
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finish:
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free(lbase_dir);
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free(rbase_dir);
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strbuf_release(&ldir);
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strbuf_release(&rdir);
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strbuf_release(&wtdir);
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@ -393,6 +393,25 @@ test_expect_success 'setup change in subdirectory' '
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git commit -m "modified both"
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'
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test_expect_success 'difftool -d with growing paths' '
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a=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa &&
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git init growing &&
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(
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cd growing &&
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echo "test -f \"\$2/b\"" | write_script .git/test-for-b.sh &&
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one=$(printf 1 | git hash-object -w --stdin) &&
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two=$(printf 2 | git hash-object -w --stdin) &&
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git update-index --add \
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--cacheinfo 100644,$one,$a --cacheinfo 100644,$two,b &&
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tree1=$(git write-tree) &&
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git update-index --add \
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--cacheinfo 100644,$two,$a --cacheinfo 100644,$one,b &&
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tree2=$(git write-tree) &&
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git checkout -- $a &&
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git difftool -d --extcmd .git/test-for-b.sh $tree1 $tree2
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)
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'
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run_dir_diff_test () {
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test_expect_success "$1 --no-symlinks" "
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symlinks=--no-symlinks &&
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