linux-hardening - Re: [PATCH] qnx4: fix to avoid panic due to buffer overflow

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Date: Sun, 12 Nov 2023 17:16:32 +0100
From: Anders Larsen <al@...rsen.net>
To: Ronald Monthero <debug.penguin32@...il.com>
Cc: keescook@...omium.org, gustavoars@...nel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, Niek Nooijens <nieknooijens@...il.com>
Subject: Re: [PATCH] qnx4: fix to avoid panic due to buffer overflow

On 2023-11-12 10:53 Ronald Monthero wrote:
> qnx4 dir name length can vary to be of maximum size
> QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX depending on whether
> 'link info' entry is stored and the status byte is set.
> So to avoid buffer overflow check di_fname length
> fetched from (struct qnx4_inode_entry *)
> before use in strlen to avoid buffer overflow.

[snip]

> 
> Signed-off-by: Ronald Monthero <debug.penguin32@...il.com>
> ---
>  fs/qnx4/namei.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> index 8d72221735d7..825b891a52b3 100644
> --- a/fs/qnx4/namei.c
> +++ b/fs/qnx4/namei.c
> @@ -40,6 +40,13 @@ static int qnx4_match(int len, const char *name,
>  	} else {
>  		namelen = QNX4_SHORT_NAME_MAX;
>  	}
> +
> +	/** qnx4 dir name length can vary, check the di_fname
> +	 * fetched from (struct qnx4_inode_entry *) before use in
> +	 * strlen to avoid panic due to buffer overflow"
> +	 */
> +	if (strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
> +		return -ENAMETOOLONG;

sizeof(de->di_fname) equals QNX4_SHORT_NAME_MAX, so this test fails as soon as 
a filename is longer than that!

This quick fix (untested!) should do the trick (and avoids computing the length 
of the name twice):

diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
index 8d72221735d7..7694f86fbb2e 100644
--- a/fs/qnx4/namei.c
+++ b/fs/qnx4/namei.c
@@ -40,9 +40,7 @@ static int qnx4_match(int len, const char *name,
 	} else {
 		namelen = QNX4_SHORT_NAME_MAX;
 	}
-	thislen = strlen( de->di_fname );
-	if ( thislen > namelen )
-		thislen = namelen;
+	thislen = strnlen(de->di_fname, namelen);
 	if (len != thislen) {
 		return 0;
 	}

Cheers
Anders