[PATCH] ide-cd: prevent null pointer deref via cdrom_newpc_intr

From: Rainer Weikusat
Date: Thu Jun 18 2009 - 09:56:40 EST

From: Rainer Weikusat <rweikusat@xxxxxxxxxxx>

With 2.6.30, the error handling code in cdrom_newpc_intr was changed
to deal with partial request failures by normally completing the 'good'
parts of a request and only 'error' the last (and presumably,
incompletely transferred) bio associated with a particular
request. This doesn't work for requests which don't have bios
associated with them ('GPCMD_READ_DISC_INFO'), because the first call
to ide_end_rq, done via ide_complete_rq in order to do the
partial completion part, returns with a code of zero for all non-bio
requests, causing the drive->hwif->rq pointer to be set to NULL. Upon
calling ide_complete_rq a second time, it is attempted to de-reference
this null pointer, resulting in a kernel crash.

Signed-Off-By: Rainer Weikusat <rweikusat@xxxxxxxxxxx>


This is fixed in the linux-ide tree since at about 2009/06/10 [Bug
13399, also happens w/ TSSTcorpDVD-ROM SH-D162C], but a patch
against 2.6.30 AFAIK doesn't exist (and I didn't find the
corresponding thread before digging through all of this ...).

--- drivers/ide/ide-cd.c.orig 2009-06-18 15:10:24.000000000 +0200
+++ drivers/ide/ide-cd.c 2009-06-18 14:10:16.000000000 +0200
@@ -758,7 +758,7 @@ out_end:
rq->errors = -EIO;

- if (uptodate == 0)
+ if (uptodate == 0 && rq->bio)
ide_cd_error_cmd(drive, cmd);

/* make sure it's fully ended */
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