svn commit: r335655 - head/sbin/fsck_msdosfs
Xin LI
delphij at FreeBSD.org
Tue Jun 26 06:19:00 UTC 2018
Author: delphij
Date: Tue Jun 26 06:18:59 2018
New Revision: 335655
URL: https://svnweb.freebsd.org/changeset/base/335655
Log:
Fix division by zero when reading boot block by postponing division
until it is necessary and after we validated bytes per sector is non-
zero.
Obtained from: Android https://android-review.googlesource.com/c/platform/external/fsck_msdos/+/36362
MFC after: 2 weeks
Modified:
head/sbin/fsck_msdosfs/boot.c
Modified: head/sbin/fsck_msdosfs/boot.c
==============================================================================
--- head/sbin/fsck_msdosfs/boot.c Tue Jun 26 04:06:49 2018 (r335654)
+++ head/sbin/fsck_msdosfs/boot.c Tue Jun 26 06:18:59 2018 (r335655)
@@ -178,12 +178,8 @@ readboot(int dosfs, struct bootblock *boot)
/* Check backup bpbFSInfo? XXX */
}
- boot->ClusterOffset = (boot->bpbRootDirEnts * 32 +
- boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
- boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
- CLUST_FIRST * boot->bpbSecPerClust;
-
- if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE_REAL != 0) {
+ if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE_REAL != 0 ||
+ boot->bpbBytesPerSec == 0) {
pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
return FSFATAL;
}
@@ -196,6 +192,10 @@ readboot(int dosfs, struct bootblock *boot)
boot->NumSectors = boot->bpbSectors;
} else
boot->NumSectors = boot->bpbHugeSectors;
+ boot->ClusterOffset = (boot->bpbRootDirEnts * 32 +
+ boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
+ boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
+ CLUST_FIRST * boot->bpbSecPerClust;
boot->NumClusters = (boot->NumSectors - boot->ClusterOffset) /
boot->bpbSecPerClust;
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