+ nilfs2-fix-null-ptr-deref-in-block_touch_buffer-tracepoint.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: nilfs2: fix null-ptr-deref in block_touch_buffer tracepoint
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     nilfs2-fix-null-ptr-deref-in-block_touch_buffer-tracepoint.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/nilfs2-fix-null-ptr-deref-in-block_touch_buffer-tracepoint.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Subject: nilfs2: fix null-ptr-deref in block_touch_buffer tracepoint
Date: Thu, 7 Nov 2024 01:07:32 +0900

Patch series "nilfs2: fix null-ptr-deref bugs on block tracepoints".

This series fixes null pointer dereference bugs that occur when using
nilfs2 and two block-related tracepoints.


This patch (of 2):

It has been reported that when using "block:block_touch_buffer"
tracepoint, touch_buffer() called from __nilfs_get_folio_block() causes a
NULL pointer dereference, or a general protection fault when KASAN is
enabled.

This happens because since the tracepoint was added in touch_buffer(), it
references the dev_t member bh->b_bdev->bd_dev regardless of whether the
buffer head has a pointer to a block_device structure.  In the current
implementation, the block_device structure is set after the function
returns to the caller.

Here, touch_buffer() is used to mark the folio/page that owns the buffer
head as accessed, but the common search helper for folio/page used by the
caller function was optimized to mark the folio/page as accessed when it
was reimplemented a long time ago, eliminating the need to call
touch_buffer() here in the first place.

So this solves the issue by eliminating the touch_buffer() call itself.

Link: https://lkml.kernel.org/r/20241106160811.3316-1-konishi.ryusuke@gmail.com
Link: https://lkml.kernel.org/r/20241106160811.3316-2-konishi.ryusuke@gmail.com
Fixes: 5305cb830834 ("block: add block_{touch|dirty}_buffer tracepoint")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: Ubisectech Sirius <bugreport@valiantsec.com>
Closes: https://lkml.kernel.org/r/86bd3013-887e-4e38-960f-ca45c657f032.bugreport@valiantsec.com
Reported-by: syzbot+9982fb8d18eba905abe2@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9982fb8d18eba905abe2
Tested-by: syzbot+9982fb8d18eba905abe2@syzkaller.appspotmail.com
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>


Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/nilfs2/page.c |    1 -
 1 file changed, 1 deletion(-)

--- a/fs/nilfs2/page.c~nilfs2-fix-null-ptr-deref-in-block_touch_buffer-tracepoint
+++ a/fs/nilfs2/page.c
@@ -39,7 +39,6 @@ static struct buffer_head *__nilfs_get_f
 	first_block = (unsigned long)index << (PAGE_SHIFT - blkbits);
 	bh = get_nth_bh(bh, block - first_block);
 
-	touch_buffer(bh);
 	wait_on_buffer(bh);
 	return bh;
 }
_

Patches currently in -mm which might be from konishi.ryusuke@gmail.com are

nilfs2-fix-null-ptr-deref-in-block_touch_buffer-tracepoint.patch
nilfs2-fix-null-ptr-deref-in-block_dirty_buffer-tracepoint.patch