Re: [PATCH] liveupdate: check for duplicate session before growing block set

[Pasha Tatashin]

On 11-03 12:39, Christian Aurich Zanettini Martins wrote:
> luo_session_insert() grows the outgoing block set before checking for a
> duplicate session name. On -EEXIST the new block stays in the set.
> 
> If the session count is an exact multiple of the per-block capacity (51
> with 4K pages), that block stays empty. It is serialized with count 0,
> which kho_block_set_restore() rejects in the next kernel:
> 
>   luo: Block contains invalid entry count: 0
>   Kernel panic - not syncing: The incoming tree failed to initialize properly [-EINVAL], disabling live update
> 
> Check for the duplicate before growing the block set, as
> luo_preserve_file() does with the token.
> 
> Fixes: 2a441a14c2c0 ("liveupdate: Remove limit on the number of sessions")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Christian Aurich Zanettini Martins <christian.aurichzm@xxxxxxxxx>
> ---
> 
> Notes:
>     Tested in QEMU: create N sessions, retry "sess-0" to get -EEXIST, then
>     kexec and retrieve them. Unpatched, the second kernel panics for N=51
>     and N=102; patched, N=1, 51, 52, 102 and 153 all come back.
> 
>     Based on v7.4-rc1.
> 
>  kernel/liveupdate/luo_session.c | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
> index f48e9a4185f9..74bc66929f4b 100644
> --- a/kernel/liveupdate/luo_session.c
> +++ b/kernel/liveupdate/luo_session.c
> @@ -176,16 +176,6 @@ static int luo_session_insert(struct luo_session_header *sh,
>  
>  	guard(rwsem_write)(&sh->rwsem);
>  
> -	/*
> -	 * For outgoing we should make sure there is room in serialization array
> -	 * for new session.
> -	 */
> -	if (sh == &luo_session_global.outgoing) {
> -		err = kho_block_set_grow(&sh->block_set, sh->count + 1);
> -		if (err)
> -			return err;
> -	}
> -
>  	/*
>  	 * For small number of sessions this loop won't hurt performance
>  	 * but if we ever start using a lot of sessions, this might
> @@ -196,6 +186,17 @@ static int luo_session_insert(struct luo_session_header *sh,
>  		if (!strncmp(it->name, session->name, sizeof(it->name)))
>  			return -EEXIST;
>  	}
> +
> +	/*
> +	 * For outgoing we should make sure there is room in serialization array
> +	 * for new session.
> +	 */
> +	if (sh == &luo_session_global.outgoing) {
> +		err = kho_block_set_grow(&sh->block_set, sh->count + 1);
> +		if (err)
> +			return err;
> +	}
> +

Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>