On Tue, 2023-04-11 at 09:42 -0700, Casey Schaufler wrote: > On 4/11/2023 12:53 AM, Roberto Sassu wrote: > > 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. > > To be clear, Smack may use two xattrs from smack_inode_init_security(), > SMACK64 and SMACK64_TRANSMUTE. SMACK64_TRANSMUTE is only set on directories. > SMACK64_MMAP and SMACK64_EXEC can be set on files, but they have to be > set explicitly. A file may have three xattrs, but only one from > smack_inode_init_security(). > > I'm looking at the existing Smack function, and it includes checking for > the transmute attribute. Your patch seems to have dropped this important > behavior. That needs to be restored in any case. You can tell that you need > to include the SMACK64_TRANSMUTE xattr if setting it is detected. Uhm, I think it is simply omitted in the patch, not deleted. I just sent a draft of the modifications required to set SMACK64_TRANSMUTE in smack_inode_init_security(). Roberto > > > > 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 > >
