1*4882a593SmuzhiyunFrom 34b85a6e07014383ddcad09f99ff239ad752dd1a Mon Sep 17 00:00:00 2001 2*4882a593SmuzhiyunFrom: Daniel Axtens <dja@axtens.net> 3*4882a593SmuzhiyunDate: Fri, 15 Jan 2021 13:29:53 +1100 4*4882a593SmuzhiyunSubject: [PATCH] video/readers/jpeg: Catch OOB reads/writes in 5*4882a593Smuzhiyun grub_jpeg_decode_du() 6*4882a593Smuzhiyun 7*4882a593SmuzhiyunThe key line is: 8*4882a593Smuzhiyun 9*4882a593Smuzhiyun du[jpeg_zigzag_order[pos]] = val * (int) data->quan_table[qt][pos]; 10*4882a593Smuzhiyun 11*4882a593Smuzhiyunjpeg_zigzag_order is grub_uint8_t[64]. 12*4882a593Smuzhiyun 13*4882a593SmuzhiyunI don't understand JPEG decoders quite well enough to explain what's 14*4882a593Smuzhiyungoing on here. However, I observe sometimes pos=64, which leads to an 15*4882a593SmuzhiyunOOB read of the jpeg_zigzag_order global then an OOB write to du. 16*4882a593SmuzhiyunThat leads to various unpleasant memory corruption conditions. 17*4882a593Smuzhiyun 18*4882a593SmuzhiyunCatch where pos >= ARRAY_SIZE(jpeg_zigzag_order) and bail. 19*4882a593Smuzhiyun 20*4882a593SmuzhiyunSigned-off-by: Daniel Axtens <dja@axtens.net> 21*4882a593SmuzhiyunReviewed-by: Daniel Kiper <daniel.kiper@oracle.com> 22*4882a593SmuzhiyunSigned-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com> 23*4882a593Smuzhiyun--- 24*4882a593Smuzhiyun grub-core/video/readers/jpeg.c | 8 ++++++++ 25*4882a593Smuzhiyun 1 file changed, 8 insertions(+) 26*4882a593Smuzhiyun 27*4882a593Smuzhiyundiff --git a/grub-core/video/readers/jpeg.c b/grub-core/video/readers/jpeg.c 28*4882a593Smuzhiyunindex 23f919a..e514812 100644 29*4882a593Smuzhiyun--- a/grub-core/video/readers/jpeg.c 30*4882a593Smuzhiyun+++ b/grub-core/video/readers/jpeg.c 31*4882a593Smuzhiyun@@ -526,6 +526,14 @@ grub_jpeg_decode_du (struct grub_jpeg_data *data, int id, jpeg_data_unit_t du) 32*4882a593Smuzhiyun val = grub_jpeg_get_number (data, num & 0xF); 33*4882a593Smuzhiyun num >>= 4; 34*4882a593Smuzhiyun pos += num; 35*4882a593Smuzhiyun+ 36*4882a593Smuzhiyun+ if (pos >= ARRAY_SIZE (jpeg_zigzag_order)) 37*4882a593Smuzhiyun+ { 38*4882a593Smuzhiyun+ grub_error (GRUB_ERR_BAD_FILE_TYPE, 39*4882a593Smuzhiyun+ "jpeg: invalid position in zigzag order!?"); 40*4882a593Smuzhiyun+ return; 41*4882a593Smuzhiyun+ } 42*4882a593Smuzhiyun+ 43*4882a593Smuzhiyun du[jpeg_zigzag_order[pos]] = val * (int) data->quan_table[qt][pos]; 44*4882a593Smuzhiyun pos++; 45*4882a593Smuzhiyun } 46*4882a593Smuzhiyun-- 47*4882a593Smuzhiyun2.14.2 48*4882a593Smuzhiyun 49