[PATCH] checkpatch: Only encode UTF-8 quoted printable mail headers

[Geert Uytterhoeven <geert+renesas@glider.be>]

As PERL uses its own internal character encoding, always calling
encode("utf8", ...) on the author name may cause corruption, leading to
an author signoff mismatch.

This happens in the following cases:
  - If a patch is in ISO-8859, and contains a non-ASCII author name in
    the From: line, it is converted to UTF-8, while the Signed-off-by
    line will still be in ISO-8859.
  - If a patch is in UTF-8, and contains a non-ASCII author name in the
    body (not header) From: line, it is assumed to be encoded in PERL's
    internal character encoding, and converted to UTF-8 incorrectly,
    while the Signed-off-by line will be in real UTF-8.

Fix this by only doing the encode step if the From: line used UTF-8
quoted printable encoding.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Fixes: bc76e3a125b44379 ("checkpatch: warn if missing author Signed-off-by")
in -next

To be folded into "checkpatch: Warn if missing author Signed-off-by" in
Andrew's tree.
---
 scripts/checkpatch.pl | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 3d01fee203c4775d..e847377779e7804f 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2523,7 +2523,8 @@ sub process {
 
 # Check the patch for a From:
 		if (decode("MIME-Header", $line) =~ /^From:\s*(.*)/) {
-			$author = encode("utf8", $1);
+			$author = $1;
+			$author = encode("utf8", $author) if $line =~ /=\?utf-8\?/i;
 			$author =~ s/"//g;
 		}
 
-- 
2.17.1