Re: [PATCH] fs/ntfs: Check at->attr_cur after calling next_attribute()

From: Andreas Klauer <andreas.klauer@metamorpher.de>
To: The development of GNU GRUB <grub-devel@gnu.org>
Cc: B Horn <b@horn.uk>, Andreas Klauer <andreas.klauer@metamorpher.de>
Subject: Re: [PATCH] fs/ntfs: Check at->attr_cur after calling next_attribute()
Date: Fri, 28 Feb 2025 21:58:33 +0100	[thread overview]
Message-ID: <Z8IjefifS-dpHr-4@memoxo.de> (raw)
In-Reply-To: <20250228130739.84606-2-b@horn.uk>

On Fri, Feb 28, 2025 at 01:07:06PM +0000, B Horn wrote:
> On some NTFS volumes GRUB would enter an infinite loop when
> next_attribute() returned NULL, which can happen in normal cases when
> the end of the attribute list is reached.
> This would trigger a NULL deref, but as the null page is mapped on the
> majority of firmware, an infinite loop would occur as the while loop
> didn't make any progress.
> 
> Fixing this by verifying the value of at->attr_cur on the next iteration
> of the loop, after it has been set to the result of next_attribute().
> Also removing the redundant check against mft_end as the
> next_attribute() should handle that now.
> A pointer to the end of the buffer is stored in at->end, which is
> initialized the same way as mft_end was.
> 
> Fixes: https://savannah.gnu.org/bugs/index.php?66855
> 
> Reported-by: Andreas Klauer <andreas.klauer@metamorpher.de>
> Signed-off-by: B Horn <b@horn.uk>

Thank you, it works fine here.

Regards
Andreas

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