Fix CSN1 decoding: CSN_LEFT_ALIGNED_VAR_BMP bounds

Fix attempted read past vector boundaries in case of a starting bit offset !=
0, so that the last amount of bits read should be < 8. In the case of
CSN_LEFT_ALIGNED_VAR_BMP, the mod-8 calculation was flawed, and in the final
step, 8 bits were read instead of the remainder < 8. This lead to -EINVAL being
returned by bitvec_get_bit_pos() and bogus resulting data.

Instead, read 8 bits only as long as at least 8 bits remain, and read any
remaining bits < 8 in a final step. Drop unneeded nB1 variable and an obvious
comment.

Adjust the unit test assertion in testCsnLeftAlignedVarBmpBounds() in
RLCMACTest.cpp.

Based on a fix by Aravind Sirsikar <Arvind.Sirsikar@radisys.com>, but
implemented differently.

Related: OS#1805
Change-Id: I490498c8da6b531f54acb673379379f7b10907c0

1 files changed, 5 insertions, 6 deletions

diff --git a/src/csn1.cpp b/src/csn1.cpp
index d51fe83e..a1698a58 100644
--- a/src/csn1.cpp
+++ b/src/csn1.cpp
@@ -1110,22 +1110,21 @@ csnStreamDecoder(csnStream_t* ar, const CSN_DESCR* pDescr, bitvec *vector, unsig
 
           { /* extract bits */
             guint8* pui8 = pui8DATA(data, pDescr->offset);
-            gint16 nB1  = no_of_bits & 0x07;/* no_of_bits Mod 8 */
 
-            while (no_of_bits > 0)
+            while (no_of_bits >= 8)
             {
               *pui8 = bitvec_read_field(vector, readIndex, 8);
               LOGPC(DCSN1, LOGL_NOTICE, "%s = %u | ", pDescr->sz , (unsigned)*pui8);
               pui8++;
               no_of_bits -= 8;
             }
-            if (nB1 > 0)
+            if (no_of_bits > 0)
             { 
-              *pui8 = bitvec_read_field(vector, readIndex, nB1);
+              *pui8 = bitvec_read_field(vector, readIndex, no_of_bits);
               LOGPC(DCSN1, LOGL_NOTICE, "%s = %u | ", pDescr->sz , (unsigned)*pui8);
               pui8++;
-              no_of_bits  -= nB1;
-              bit_offset += nB1; /* (nB1 is no_of_bits Mod 8) */
+              bit_offset += no_of_bits;
+              no_of_bits = 0;
             }
           }
         }