linux-kernel - NULL pointer dereference in print_daily_error

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Message-ID: <20100914125102.GA5318@swordfish.minsk.epam.com>
Date:	Tue, 14 Sep 2010 15:51:02 +0300
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Andreas Dilger <adilger.kernel@...ger.ca>, Jan Kara <jack@...e.cz>,
	Eric Sandeen <sandeen@...hat.com>,
	Christoph Hellwig <hch@....de>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: NULL pointer dereference in print_daily_error_info

Hello,

This patch fixes NULL pointer dereference in print_daily_error_info, when   
called
on unmounted fs (EXT4_SB(sb) returns NULL). Deleting error reporting timer  
in
ext4_put_super fixes oops.

IRQ:
run_timer_softirq
?run_timer_softirq
print_daily_error_info
?__do_softirq
__do_softirq
call_softirq
do_softirq
irq_exit
smp_apic_timer_interrupt
apic_timer_interrupt
EOI
intel_idle
intel_idle
...

By the way, isn't print_daily_error_info racy? Is it safe to call           
print_daily_error_info
(by timer event (softirq)) when we'are remounting fs, etc.?

Please kindly review.

---

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2614774..751997d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -719,6 +719,7 @@ static void ext4_put_super(struct super_block *sb)
 			ext4_abort(sb, "Couldn't clean up the journal");
 	}

+	del_timer(&sbi->s_err_report);
 	ext4_release_system_zone(sb);
 	ext4_mb_release(sb);
 	ext4_ext_release(sb);

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