File handle-incomplete-last-track of Package grub

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File handle-incomplete-last-track of Package grub

From: Alexander Graf <agraf@suse.de>
Subject: [PATCH] Fix grub access to incomplete tracks
Date: Wed, 14 Dec 2011 18:23:00 +0100

When we have a disk in our system that has an LBA count that exceeds the track
boundary limits, grub still tries to read all of the track into its buffer.

This fails for obvious reasons, but can be easily circumvented: Just cap the
amount of sectors we want to read to a sensible amount. That way we don't read
beyond the end of the disk and the buffer is filled with sensible data up to
the point where the higher layers should care about the data.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Balazs Kutil <bkutil@suse.cz>
Acked-by: Torsten Duwe <duwe@suse.de>

diff --git a/stage2/bios.c b/stage2/bios.c
index 2d85e40..e3ad774 100644
--- a/stage2/bios.c
+++ b/stage2/bios.c
@@ -66,5 +66,11 @@ biosdisk (int read, int drive, struct geometry *geometry,
 #endif /* NO_BUGGY_BIOS_IN_THE_WORLD */
 
+      /* For incomplete last tracks, just read as much as we can */
+      if ((sector < geometry->total_sectors) &&
+          (sector + nsec) > geometry->total_sectors) {
+          nsec = geometry->total_sectors - sector;
+      }
+
       /* FIXME: sizeof (DAP) must be 0x10. Should assert that the compiler
 	 can't add any padding.  */
       dap.length = sizeof (dap);

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