linux-kernel - Re: [PATCH] jfs: Use unsigned variable for length calculations

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Message-ID: <Y96/SUlPUl7xH1NO@gallifrey>
Date:   Sat, 4 Feb 2023 20:25:45 +0000
From:   "Dr. David Alan Gilbert" <linux@...blig.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Dave Kleikamp <shaggy@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Dave Chinner <dchinner@...hat.com>,
        jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] jfs: Use unsigned variable for length calculations

* Kees Cook (keescook@...omium.org) wrote:
> To avoid confusing the compiler about possible negative sizes, switch
> "ssize" which can never be negative from int to u32.  Seen with GCC 13:
> 
> ../fs/jfs/namei.c: In function 'jfs_symlink': ../include/linux/fortify-string.h:57:33: warning: '__builtin_memcpy' pointer overflow between offset 0 and size [-2147483648, -1]
> [-Warray-bounds=]
>    57 | #define __underlying_memcpy     __builtin_memcpy
>       |                                 ^
> ...
> ../fs/jfs/namei.c:950:17: note: in expansion of macro 'memcpy'
>   950 |                 memcpy(ip->i_link, name, ssize);
>       |                 ^~~~~~
> 
> Cc: Dave Kleikamp <shaggy@...nel.org>
> Cc: Christian Brauner <brauner@...nel.org>
> Cc: Dave Chinner <dchinner@...hat.com>
> Cc: jfs-discussion@...ts.sourceforge.net
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  fs/jfs/namei.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/jfs/namei.c b/fs/jfs/namei.c
> index b29d68b5eec5..494b9f4043cf 100644
> --- a/fs/jfs/namei.c
> +++ b/fs/jfs/namei.c
> @@ -876,7 +876,7 @@ static int jfs_symlink(struct mnt_idmap *idmap, struct inode *dip,
>  	tid_t tid;
>  	ino_t ino = 0;
>  	struct component_name dname;
> -	int ssize;		/* source pathname size */
> +	u32 ssize;		/* source pathname size */

Had you considered using size_t - this is set from a strlen and used by a memcpy
that both talk size_t.

Dave

>  	struct btstack btstack;
>  	struct inode *ip = d_inode(dentry);
>  	s64 xlen = 0;
> @@ -957,7 +957,7 @@ static int jfs_symlink(struct mnt_idmap *idmap, struct inode *dip,
>  		if (ssize > sizeof (JFS_IP(ip)->i_inline))
>  			JFS_IP(ip)->mode2 &= ~INLINEEA;
>  
> -		jfs_info("jfs_symlink: fast symlink added  ssize:%d name:%s ",
> +		jfs_info("jfs_symlink: fast symlink added  ssize:%u name:%s ",
>  			 ssize, name);
>  	}
>  	/*
> @@ -987,7 +987,7 @@ static int jfs_symlink(struct mnt_idmap *idmap, struct inode *dip,
>  		ip->i_size = ssize - 1;
>  		while (ssize) {
>  			/* This is kind of silly since PATH_MAX == 4K */
> -			int copy_size = min(ssize, PSIZE);
> +			u32 copy_size = min_t(u32, ssize, PSIZE);
>  
>  			mp = get_metapage(ip, xaddr, PSIZE, 1);
>  
> -- 
> 2.34.1
> 
-- 
 -----Open up your eyes, open up your mind, open up your code -------   
/ Dr. David Alan Gilbert    |       Running GNU/Linux       | Happy  \ 
\        dave @ treblig.org |                               | In Hex /
 \ _________________________|_____ http://www.treblig.org   |_______/