On Tue, 2023-04-11 at 03:22 -0400, Mimi Zohar wrote: > Hi Roberto, > > Sorry for the delay in responding... Hi Mimi no worries! > The patch description reads as though support for per LSM multiple > xattrs is being added in this patch, though lsm_get_xattr_slot() only > ever is incremented once for each LSM. To simplify review, it would be > nice to mention that lsm_get_xattr_slot() would be called multiple > times per LSM xattr. Ok, I will mention it. > On Fri, 2023-03-31 at 14:32 +0200, Roberto Sassu wrote: > > From: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > > > Currently, security_inode_init_security() supports only one LSM providing > > an xattr and EVM calculating the HMAC on that xattr, plus other inode > > metadata. > > > > Allow all LSMs to provide one or multiple xattrs, by extending the security > > blob reservation mechanism. Introduce the new lbs_xattr_count field of the > > lsm_blob_sizes structure, so that each LSM can specify how many xattrs it > > needs, and the LSM infrastructure knows how many xattr slots it should > > allocate. > > > > Dynamically allocate the new_xattrs array to be populated by LSMs with the > > inode_init_security hook, and pass it to the latter instead of the > > name/value/len triple. Unify the !initxattrs and initxattrs case, simply > > don't allocate the new_xattrs array in the former. > > > > Also, pass to the hook the number of xattrs filled by each LSM, so that > > there are no gaps when the next LSM fills the array. Gaps might occur > > because an LSM can legitimately request xattrs to the LSM infrastructure, > > but not fill the reserved slots, if it was not initialized. > > The number of security xattrs permitted per LSM was discussed in the > second paragraph. The first line of this paragraph needs to be updated > to reflect the current number of security xattrs used, though that is > more related to the new lsm_get_xattr_slot(). Or perhaps the entire > paragraph is unnecessary, a remnant from > security_check_compact_filled_xattrs(), and should be removed. I would probably say in that paragraph that the number specified for the lbs_xattr_count field determines how many times an LSM can call lsm_get_xattr_slot(). > > Update the documentation of security_inode_init_security() to reflect the > > changes, and fix the description of the xattr name, as it is not allocated > > anymore. > > > > Finally, adapt both SELinux and Smack to use the new definition of the > > inode_init_security hook, and to fill the reserved slots in the xattr > > array. Introduce the lsm_get_xattr_slot() helper to retrieve an available > > slot to fill, and to increment the number of filled slots. > > > > Move the xattr->name assignment after the xattr->value one, so that it is > > done only in case of successful memory allocation. For Smack, also reserve > > space for the other defined xattrs although they are not set yet in > > smack_inode_init_security(). > > This Smack comment should be moved to the previous paragraph and even > expanded explaining that lsm_get_xattr_slot() will be called for each > additional security xattr. >From previous Paul's and Casey's comments, Smack will have just two xattrs, assuming that security.SMACK_TRASMUTE64 can be set in smack_inode_init_security(). I will change this part accordingly once Casey can have a look at the function. > > Reported-by: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx> (EVM crash) > > Link: https://lore.kernel.org/linux-integrity/Y1FTSIo+1x+4X0LS@archlinux/ > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > --- > > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h > > index c2be66c669a..9eb9b686493 100644 > > --- a/include/linux/lsm_hooks.h > > +++ b/include/linux/lsm_hooks.h > > @@ -28,6 +28,7 @@ > > #include <linux/security.h> > > #include <linux/init.h> > > #include <linux/rculist.h> > > +#include <linux/xattr.h> > > > > union security_list_options { > > #define LSM_HOOK(RET, DEFAULT, NAME, ...) RET (*NAME)(__VA_ARGS__); > > @@ -63,8 +64,27 @@ struct lsm_blob_sizes { > > int lbs_ipc; > > int lbs_msg_msg; > > int lbs_task; > > + int lbs_xattr_count; /* number of xattr slots in new_xattrs array */ > > }; > > > > +/** > > + * lsm_get_xattr_slot - Return the next available slot and increment the index > > + * @xattrs: array storing LSM-provided xattrs > > + * @xattr_count: number of already stored xattrs (updated) > > + * > > + * Retrieve the first available slot in the @xattrs array to fill with an xattr, > > + * and increment @xattr_count. > > + * > > + * Return: The slot to fill in @xattrs if non-NULL, NULL otherwise. > > + */ > > +static inline struct xattr *lsm_get_xattr_slot(struct xattr *xattrs, > > + int *xattr_count) > > +{ > > + if (unlikely(!xattrs)) > > + return NULL; > > + return xattrs + (*xattr_count)++; > > At some point, since lsm_get_xattr_slot() could be called multiple > times from the same LSM, shouldn't there be some sort of bounds > checking? >From previous Paul's comments, I understood that he prefers to avoid extra checks. It will be up to LSM developers to ensure that the API is used correctly. Thanks Roberto
