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fix "git apply --index ..." not to deref NULL

I noticed this when "git am CORRUPTED" unexpectedly failed with an
odd diagnostic, and even removed one of the files it was supposed
to have patched.

Reproduce with any valid old/new patch from which you have removed
the "+++ b/FILE" line.  You'll see a diagnostic like this

    fatal: unable to write file '(null)' mode 100644: Bad address

and you'll find that FILE has been removed.

The above is on glibc-based systems.  On other systems, rather than
getting "null", you may provoke a segfault as git tries to
dereference the NULL file name.

Signed-off-by: Jim Meyering <meyering@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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meyering authored and gitster committed Oct 12, 2011
1 parent 7ed863a commit 2c93286ab2ca5271e26779ffd1ecfd1c7a082a41
Showing with 46 additions and 0 deletions.
  1. +3 −0 builtin/apply.c
  2. +43 −0 t/t4254-am-corrupt.sh
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@@ -1405,6 +1405,9 @@ static int find_header(char *line, unsigned long size, int *hdrsize, struct patc
"%d leading pathname components (line %d)" , p_value, linenr);
patch->old_name = patch->new_name = patch->def_name;
}
+ if (!patch->is_delete && !patch->new_name)
+ die("git diff header lacks filename information "
+ "(line %d)", linenr);
patch->is_toplevel_relative = 1;
*hdrsize = git_hdr_len;
return offset;
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@@ -0,0 +1,43 @@
+#!/bin/sh
+
+test_description='git am with corrupt input'
+. ./test-lib.sh
+
+# Note the missing "+++" line:
+cat > bad-patch.diff <<'EOF'
+From: A U Thor <au.thor@example.com>
+diff --git a/f b/f
+index 7898192..6178079 100644
+--- a/f
+@@ -1 +1 @@
+-a
++b
+EOF
+
+test_expect_success setup '
+ test $? = 0 &&
+ echo a > f &&
+ git add f &&
+ test_tick &&
+ git commit -m initial
+'
+
+# This used to fail before, too, but with a different diagnostic.
+# fatal: unable to write file '(null)' mode 100644: Bad address
+# Also, it had the unwanted side-effect of deleting f.
+test_expect_success 'try to apply corrupted patch' '
+ git am bad-patch.diff 2> actual
+ test $? = 1
+'
+
+cat > expected <<EOF
+fatal: git diff header lacks filename information (line 4)
+EOF
+
+test_expect_success 'compare diagnostic; ensure file is still here' '
+ test $? = 0 &&
+ test -f f &&
+ test_cmp expected actual
+'
+
+test_done

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