Author: delphij Date: Sat Jan 11 17:41:20 2020 New Revision: 356636 URL: https://svnweb.freebsd.org/changeset/base/356636
Log: Correct off-by-two issue when determining FAT type. In the code we used NumClusters as the upper (non-inclusive) boundary of valid cluster number, so the actual value was 2 (CLUST_FIRST) more than the real number of clusters. This causes a FAT16 media with 65524 clusters be treated as FAT32 and might affect FAT12 media with 4084 clusters as well. To fix this, we increment NumClusters by CLUST_FIRST after the type determination. PR: 243179 MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D23082 Modified: head/sbin/fsck_msdosfs/boot.c Modified: head/sbin/fsck_msdosfs/boot.c ============================================================================== --- head/sbin/fsck_msdosfs/boot.c Sat Jan 11 16:28:35 2020 (r356635) +++ head/sbin/fsck_msdosfs/boot.c Sat Jan 11 17:41:20 2020 (r356636) @@ -266,8 +266,11 @@ readboot(int dosfs, struct bootblock *boot) return FSFATAL; } - boot->NumClusters = (boot->NumSectors - boot->FirstCluster) / boot->bpbSecPerClust + - CLUST_FIRST; + /* + * The number of clusters is derived from available data sectors, divided + * by sectors per cluster. + */ + boot->NumClusters = (boot->NumSectors - boot->FirstCluster) / boot->bpbSecPerClust; if (boot->flags & FAT32) { if (boot->NumClusters > (CLUST_RSRVD & CLUST32_MASK)) { @@ -310,11 +313,19 @@ readboot(int dosfs, struct bootblock *boot) break; } - if (boot->NumFatEntries < boot->NumClusters - CLUST_FIRST) { + if (boot->NumFatEntries < boot->NumClusters) { pfatal("FAT size too small, %u entries won't fit into %u sectors\n", boot->NumClusters, boot->FATsecs); return FSFATAL; } + + /* + * There are two reserved clusters. To avoid adding CLUST_FIRST every time + * when we perform boundary checks, we increment the NumClusters by 2, + * which is CLUST_FIRST to denote the first out-of-range cluster number. + */ + boot->NumClusters += CLUST_FIRST; + boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust; boot->NumFiles = 1; _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
