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jdarith.c: Require cinfo->Se == DCTSIZE2 - 1

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This fixes an oversight from the integration of the arithmetic entropy
codec from libjpeg (66f97e6820).  I chose
to integrate the latest implementation available at the time, which was
from jpeg-8b.  However, I naively replaced cinfo->lim_Se with
DCTSIZE2 - 1, not realizing that-- because of SmartScale-- jpeg-8b
contains additional code
(https://github.com/libjpeg-turbo/libjpeg-turbo/blob/jpeg-8b/jdinput.c#L249-L334)
that guards against illegal values of cinfo->Se >= DCTSIZE2.  Thus,
libjpeg-turbo's implementation of arithmetic decoding has never guarded
against such illegal values.  This commit restores the relevant check
from the original jpeg-6b arithmetic entropy codec patch ("jpeg-ari",
1e247ac854).

Fixes #564
This commit is contained in:
DRC
2021-11-23 09:54:23 -06:00
parent 9a2a42d8ee
commit d5554604cb
1 changed files with 2 additions and 2 deletions
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jdarith.c
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@@ -679,8 +679,8 @@ start_pass (j_decompress_ptr cinfo)
/* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
* This ought to be an error condition, but we make it a warning.
*/
if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
(cinfo->Se < DCTSIZE2 && cinfo->Se != DCTSIZE2 - 1))
if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
cinfo->Ah != 0 || cinfo->Al != 0)
WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
/* Select MCU decoding routine */
entropy->pub.decode_mcu = decode_mcu;