[glibc/google/grte/v5-2.27/master] iconv: Accept redundant shift sequences in IBM1364 [BZ #26224]

[Fangrui Song <maskray@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=77d2c2fd0d8245ce729ae7d3ba97279a4afc845a

commit 77d2c2fd0d8245ce729ae7d3ba97279a4afc845a
Author: Arjun Shankar <arjun@redhat.com>
Date:   Wed Nov 4 12:19:38 2020 +0100

    iconv: Accept redundant shift sequences in IBM1364 [BZ #26224]
    
    The IBM1364, IBM1371, IBM1388, IBM1390 and IBM1399 character sets
    share converter logic (iconvdata/ibm1364.c) which would reject
    redundant shift sequences when processing input in these character
    sets.  This led to a hang in the iconv program (CVE-2020-27618).
    
    This commit adjusts the converter to ignore redundant shift sequences
    and adds test cases for iconv_prog hangs that would be triggered upon
    their rejection.  This brings the implementation in line with other
    converters that also ignore redundant shift sequences (e.g. IBM930
    etc., fixed in commit 692de4b3960d).
    
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Diff:
---
 iconvdata/ibm1364.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/iconvdata/ibm1364.c b/iconvdata/ibm1364.c
index b833273aa8..27900c4307 100644
--- a/iconvdata/ibm1364.c
+++ b/iconvdata/ibm1364.c
@@ -157,24 +157,14 @@ enum
 									      \
     if (__builtin_expect (ch, 0) == SO)					      \
       {									      \
-	/* Shift OUT, change to DBCS converter.  */			      \
-	if (curcs == db)						      \
-	  {								      \
-	    result = __GCONV_ILLEGAL_INPUT;				      \
-	    break;							      \
-	  }								      \
+	/* Shift OUT, change to DBCS converter (redundant escape okay).  */   \
 	curcs = db;							      \
 	++inptr;							      \
 	continue;							      \
       }									      \
     if (__builtin_expect (ch, 0) == SI)					      \
       {									      \
-	/* Shift IN, change to SBCS converter.  */			      \
-	if (curcs == sb)						      \
-	  {								      \
-	    result = __GCONV_ILLEGAL_INPUT;				      \
-	    break;							      \
-	  }								      \
+	/* Shift IN, change to SBCS converter (redundant escape okay).  */    \
 	curcs = sb;							      \
 	++inptr;							      \
 	continue;							      \