linux-kernel - Re: [PATCH] ext4: Don't leak old mountpoint samples

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Message-ID: <1954206563.139982.1608239724384.JavaMail.zimbra@nod.at>
Date:   Thu, 17 Dec 2020 22:15:24 +0100 (CET)
From:   Richard Weinberger <richard@....at>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     tytso <tytso@....edu>, linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ext4: Don't leak old mountpoint samples

----- Ursprüngliche Mail -----
>>    Fix this by using strncpy() instead of strlcpy().  The superblock
>>    field is defined to be a fixed-size char array, and it is already
>>    marked using __nonstring in fs/ext4/ext4.h.  The consumer of the field
>>    in e2fsprogs already assumes that in the case of a 64+ byte mount
>>    path, that s_last_mounted will not be NUL terminated.
>> 
>>    Reported-by: Richard Weinberger <richard@....at>
>>    Signed-off-by: Theodore Ts'o <tytso@....edu>
> 
> Color me confused, but I don't see how this change makes any difference?
> If "cp" is only "/" then it will *still* not overwrite "edia/johnjdeveloper"
> at the end of the s_last_mounted array.  To my mind, the only difference
> between using strlcpy() and strncpy() would be whether the last byte in
> the array can be used or not, but doesn't affect the remaining bytes.

strncpy() zeros all remaining bytes.

Thanks,
//richard