[Devel] Re: [PATCH v6 03/10] ipc: segment key change helper introduced

[Serge Hallyn]

Quoting Stanislav Kinsbursky (skinsbursky at parallels.com):
> This patch introduces existent segment key changing infrastructure.
> New function ipc_update_key() can be used change segment key, cuid, cgid
> values. It checks for that new key is not used (except IPC_PRIVATE) prior to
> set it on existent.
> To make this possible, added copying of this fields from user-space in
> __get_compat_ipc_perm() and __get_compat_ipc64_perm() functions. Also segment
> search by key and lock were splitted into different functions, because
> ipc_update_key() doesn't need to lock the segment during check that new key is
> not used.
> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky at parallels.com>

Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>

> ---
>  ipc/compat.c |    6 ++++++
>  ipc/util.c   |   51 ++++++++++++++++++++++++++++++++++++++++++++++++---
>  ipc/util.h   |    2 ++
>  3 files changed, 56 insertions(+), 3 deletions(-)
> 
> diff --git a/ipc/compat.c b/ipc/compat.c
> index ad9518e..af30d13 100644
> --- a/ipc/compat.c
> +++ b/ipc/compat.c
> @@ -144,6 +144,9 @@ static inline int __get_compat_ipc64_perm(struct ipc64_perm *p64,
>  	err  = __get_user(p64->uid, &up64->uid);
>  	err |= __get_user(p64->gid, &up64->gid);
>  	err |= __get_user(p64->mode, &up64->mode);
> +	err |= __get_user(p64->cuid, &up64->cuid);
> +	err |= __get_user(p64->cgid, &up64->cgid);
> +	err |= __get_user(p64->key, &up64->key);
>  	return err;
>  }
>  
> @@ -155,6 +158,9 @@ static inline int __get_compat_ipc_perm(struct ipc64_perm *p,
>  	err  = __get_user(p->uid, &up->uid);
>  	err |= __get_user(p->gid, &up->gid);
>  	err |= __get_user(p->mode, &up->mode);
> +	err |= __get_user(p->cuid, &up->cuid);
> +	err |= __get_user(p->cgid, &up->cgid);
> +	err |= __get_user(p->key, &up->key);
>  	return err;
>  }
>  
> diff --git a/ipc/util.c b/ipc/util.c
> index 503946e..faae296 100644
> --- a/ipc/util.c
> +++ b/ipc/util.c
> @@ -173,7 +173,7 @@ void __init ipc_init_proc_interface(const char *path, const char *header,
>   *	@key: The key to find
>   *	
>   *	Requires ipc_ids.rw_mutex locked.
> - *	Returns the LOCKED pointer to the ipc structure if found or NULL
> + *	Returns the UNLOCKED pointer to the ipc structure if found or NULL
>   *	if not.
>   *	If key is found ipc points to the owning ipc structure
>   */
> @@ -195,7 +195,6 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
>  			continue;
>  		}
>  
> -		ipc_lock_by_ptr(ipc);
>  		return ipc;
>  	}
>  
> @@ -203,6 +202,27 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
>  }
>  
>  /**
> + *	ipc_findkey_locked	-	find and lock a key in an ipc identifier set
> + *	@ids: Identifier set
> + *	@key: The key to find
> + *
> + *	Requires ipc_ids.rw_mutex locked.
> + *	Returns the LOCKED pointer to the ipc structure if found or NULL
> + *	if not.
> + *	If key is found ipc points to the owning ipc structure
> + */
> +
> +static struct kern_ipc_perm *ipc_findkey_locked(struct ipc_ids *ids, key_t key)
> +{
> +	struct kern_ipc_perm *ipc;
> +
> +	ipc = ipc_findkey(ids, key);
> +	if (ipc)
> +		ipc_lock_by_ptr(ipc);
> +	return ipc;
> +}
> +
> +/**
>   *	ipc_get_maxid 	-	get the last assigned id
>   *	@ids: IPC identifier set
>   *
> @@ -388,7 +408,7 @@ retry:
>  	 * a new entry + read locks are not "upgradable"
>  	 */
>  	down_write(&ids->rw_mutex);
> -	ipcp = ipc_findkey(ids, params->key);
> +	ipcp = ipc_findkey_locked(ids, params->key);
>  	if (ipcp == NULL) {
>  		/* key not used */
>  		if (!(flg & IPC_CREAT))
> @@ -755,6 +775,31 @@ int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
>  }
>  
>  /**
> + * ipc_update_key - update the key of an IPC.
> + * @in:  the permission given as input.
> + * @out: the permission of the ipc to set.
> + *
> + * Common routine called by sys_shmctl(), sys_semctl(). sys_msgctl().
> + */
> +int ipc_update_key(struct ipc_ids *ids, struct ipc64_perm *in,
> +		    struct kern_ipc_perm *out)
> +{
> +
> +	if (in->key && out->key != in->key) {
> +		/*
> +		 * Check for existent segment with the same key.
> +		 * Note: ipc_ids.rw_mutex is taken for write already.
> +		 */
> +		if (ipc_findkey(ids, in->key))
> +			return -EEXIST;
> +	}
> +	out->cuid = in->cuid;
> +	out->cgid = in->cgid;
> +	out->key = in->key;
> +	return 0;
> +}
> +
> +/**
>   * ipc_update_perm - update the permissions of an IPC.
>   * @in:  the permission given as input.
>   * @out: the permission of the ipc to set.
> diff --git a/ipc/util.h b/ipc/util.h
> index 3a9e558..271bded 100644
> --- a/ipc/util.h
> +++ b/ipc/util.h
> @@ -126,6 +126,8 @@ struct kern_ipc_perm *ipc_lock(struct ipc_ids *, int);
>  
>  void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out);
>  void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out);
> +int ipc_update_key(struct ipc_ids *ids, struct ipc64_perm *in,
> +		   struct kern_ipc_perm *out);
>  int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out);
>  struct kern_ipc_perm *ipcctl_pre_down(struct ipc_namespace *ns,
>  				      struct ipc_ids *ids, int id, int cmd,
> 
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