ACK: [SRU][CVE-2019-14283][X/B/D][PATCH 1/1] floppy: fix out-of-bounds read in copy_buffer

[Tyler Hicks]

On 2019-08-01 10:45:17, Connor Kuehl wrote:
> From: Denis Efremov <efremov at ispras.ru>
> 
> CVE-2019-14283
> 
> This fixes a global out-of-bounds read access in the copy_buffer
> function of the floppy driver.
> 
> The FDDEFPRM ioctl allows one to set the geometry of a disk.  The sect
> and head fields (unsigned int) of the floppy_drive structure are used to
> compute the max_sector (int) in the make_raw_rw_request function.  It is
> possible to overflow the max_sector.  Next, max_sector is passed to the
> copy_buffer function and used in one of the memcpy calls.
> 
> An unprivileged user could trigger the bug if the device is accessible,
> but requires a floppy disk to be inserted.
> 
> The patch adds the check for the .sect * .head multiplication for not
> overflowing in the set_geometry function.
> 
> The bug was found by syzkaller.
> 
> Signed-off-by: Denis Efremov <efremov at ispras.ru>
> Tested-by: Willy Tarreau <w at 1wt.eu>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> (cherry picked from commit da99466ac243f15fbba65bd261bfc75ffa1532b6)
> Signed-off-by: Connor Kuehl <connor.kuehl at canonical.com>

Acked-by: Tyler Hicks <tyhicks at canonical.com>

Tyler

> ---
>  drivers/block/floppy.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
> index 42ae1d2d8243..7516fed84ae9 100644
> --- a/drivers/block/floppy.c
> +++ b/drivers/block/floppy.c
> @@ -3236,8 +3236,10 @@ static int set_geometry(unsigned int cmd, struct floppy_struct *g,
>  	int cnt;
>  
>  	/* sanity checking for parameters. */
> -	if (g->sect <= 0 ||
> -	    g->head <= 0 ||
> +	if ((int)g->sect <= 0 ||
> +	    (int)g->head <= 0 ||
> +	    /* check for overflow in max_sector */
> +	    (int)(g->sect * g->head) <= 0 ||
>  	    /* check for zero in F_SECT_PER_TRACK */
>  	    (unsigned char)((g->sect << 2) >> FD_SIZECODE(g)) == 0 ||
>  	    g->track <= 0 || g->track > UDP->tracks >> STRETCH(g) ||
> -- 
> 2.20.1
> 
> 
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