linux-kernel - Re: [PATCH] jfs: fix slab-out-of-bounds read in ea

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Message-ID: <2025021350-geometry-appear-9d84@gregkh>
Date: Thu, 13 Feb 2025 11:07:07 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Qasim Ijaz <qasdev00@...il.com>
Cc: shaggy@...nel.org, zhaomengmeng@...inos.cn, llfamsec@...il.com,
	ancowi69@...il.com, jfs-discussion@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	syzbot <syzbot+4e6e7e4279d046613bc5@...kaller.appspotmail.com>
Subject: Re: [PATCH] jfs: fix slab-out-of-bounds read in ea_get()

On Thu, Feb 13, 2025 at 12:20:25AM +0000, Qasim Ijaz wrote:
> During the "size_check" label in ea_get(), the code checks if the extended 
> attribute list (xattr) size matches ea_size. If not, it logs 
> "ea_get: invalid extended attribute" and calls print_hex_dump().
> 
> Here, EALIST_SIZE(ea_buf->xattr) returns 4110417968, which exceeds 
> INT_MAX (2,147,483,647). Then ea_size is clamped:
> 
> 	int size = clamp_t(int, ea_size, 0, EALIST_SIZE(ea_buf->xattr));
> 
> Although clamp_t aims to bound ea_size between 0 and 4110417968, the upper 
> limit is treated as an int, causing an overflow above 2^31 - 1. This leads 
> "size" to wrap around and become negative (-184549328).
> 
> The "size" is then passed to print_hex_dump() (called "len" in 
> print_hex_dump()), it is passed as type size_t (an unsigned 
> type), this is then stored inside a variable called 
> "int remaining", which is then assigned to "int linelen" which 
> is then passed to hex_dump_to_buffer(). In print_hex_dump() 
> the for loop, iterates through 0 to len-1, where len is 
> 18446744073525002176, calling hex_dump_to_buffer() 
> on each iteration:
> 
> 	for (i = 0; i < len; i += rowsize) {
> 		linelen = min(remaining, rowsize);
> 		remaining -= rowsize;
> 
> 		hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize,
> 				   linebuf, sizeof(linebuf), ascii);
> 	
> 		...
> 	}
> 	
> The expected stopping condition (i < len) is effectively broken 
> since len is corrupted and very large. This eventually leads to 
> the "ptr+i" being passed to hex_dump_to_buffer() to get closer 
> to the end of the actual bounds of "ptr", eventually an out of 
> bounds access is done in hex_dump_to_buffer() in the following 
> for loop:
> 
> 	for (j = 0; j < len; j++) {
> 			if (linebuflen < lx + 2)
> 				goto overflow2;
> 			ch = ptr[j];
> 		...
> 	}
> 
> To fix this we should validate "EALIST_SIZE(ea_buf->xattr)" 
> before it is utilised.
> 
> Reported-by: syzbot <syzbot+4e6e7e4279d046613bc5@...kaller.appspotmail.com>
> Tested-by: syzbot <syzbot+4e6e7e4279d046613bc5@...kaller.appspotmail.com>
> Closes: https://syzkaller.appspot.com/bug?extid=4e6e7e4279d046613bc5
> Fixes: d9f9d96136cb ("jfs: xattr: check invalid xattr size more strictly")
> Signed-off-by: Qasim Ijaz <qasdev00@...il.com>
> ---
>  fs/jfs/xattr.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/jfs/xattr.c b/fs/jfs/xattr.c
> index 24afbae87225..7575c51cce9b 100644
> --- a/fs/jfs/xattr.c
> +++ b/fs/jfs/xattr.c
> @@ -559,11 +555,16 @@ static int ea_get(struct inode *inode, struct ea_buffer *ea_buf, int min_size)
>  
>        size_check:
>  	if (EALIST_SIZE(ea_buf->xattr) != ea_size) {
> -		int size = clamp_t(int, ea_size, 0, EALIST_SIZE(ea_buf->xattr));
> -
> -		printk(KERN_ERR "ea_get: invalid extended attribute\n");
> -		print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1,
> -				     ea_buf->xattr, size, 1);
> +		if (unlikely(EALIST_SIZE(ea_buf->xattr) > INT_MAX)) {
> +			printk(KERN_ERR "ea_get: extended attribute size too large: %u > INT_MAX\n",
> +			       EALIST_SIZE(ea_buf->xattr));
> +		} else {
> +			int size = clamp_t(int, ea_size, 0, EALIST_SIZE(ea_buf->xattr));
> +
> +			printk(KERN_ERR "ea_get: invalid extended attribute\n");
> +			print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1,
> +				       ea_buf->xattr, size, 1);
> +		}
>  		ea_release(inode, ea_buf);
>  		rc = -EIO;
>  		goto clean_up;
> -- 
> 2.39.5
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- You have marked a patch with a "Fixes:" tag for a commit that is in an
  older released kernel, yet you do not have a cc: stable line in the
  signed-off-by area at all, which means that the patch will not be
  applied to any older kernel releases.  To properly fix this, please
  follow the documented rules in the
  Documentation/process/stable-kernel-rules.rst file for how to resolve
  this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot