> From: Casey Schaufler [mailto:casey@xxxxxxxxxxxxxxxx] > Sent: Thursday, April 22, 2021 5:46 PM > On 4/22/2021 6:46 AM, Roberto Sassu wrote: > >> From: Casey Schaufler [mailto:casey@xxxxxxxxxxxxxxxx] > >> Sent: Thursday, April 22, 2021 12:44 AM > >> On 4/21/2021 9:19 AM, Roberto Sassu wrote: > >>> In preparation for moving EVM to the LSM infrastructure, this patch > >>> replaces the name, value, len triple with the xattr array pointer provided > >>> by security_inode_init_security(). LSMs are expected to call the new > >>> function lsm_find_xattr_slot() to find the first unused slot of the array > >>> where the xattr should be written. > >>> > >>> This patch modifies also SELinux and Smack to search for an unused slot, to > >>> have a consistent behavior across LSMs (the unmodified version would > >>> overwrite the xattr set by the first LSM in the chain). It is also > >>> desirable to have the modification in those LSMs, as they are likely used > >>> as a reference for the development of new LSMs. > >> This looks better than V1. One safety comment below. > >> > >>> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > >>> --- > >>> include/linux/lsm_hook_defs.h | 4 ++-- > >>> include/linux/lsm_hooks.h | 18 +++++++++++++++--- > >>> security/security.c | 13 +++++++------ > >>> security/selinux/hooks.c | 13 ++++++------- > >>> security/smack/smack_lsm.c | 20 +++++++++----------- > >>> 5 files changed, 39 insertions(+), 29 deletions(-) > >>> > >>> diff --git a/include/linux/lsm_hook_defs.h > b/include/linux/lsm_hook_defs.h > >>> index 477a597db013..afb9dd122f60 100644 > >>> --- a/include/linux/lsm_hook_defs.h > >>> +++ b/include/linux/lsm_hook_defs.h > >>> @@ -111,8 +111,8 @@ LSM_HOOK(int, 0, path_notify, const struct path > >> *path, u64 mask, > >>> LSM_HOOK(int, 0, inode_alloc_security, struct inode *inode) > >>> LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode > *inode) > >>> LSM_HOOK(int, 0, inode_init_security, struct inode *inode, > >>> - struct inode *dir, const struct qstr *qstr, const char **name, > >>> - void **value, size_t *len) > >>> + struct inode *dir, const struct qstr *qstr, struct xattr *xattrs, > >>> + void *fs_data) > >>> LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode, > >>> const struct qstr *name, const struct inode *context_inode) > >>> LSM_HOOK(int, 0, inode_create, struct inode *dir, struct dentry *dentry, > >>> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h > >>> index c5498f5174ce..e8c9bac29b9d 100644 > >>> --- a/include/linux/lsm_hooks.h > >>> +++ b/include/linux/lsm_hooks.h > >>> @@ -27,6 +27,7 @@ > >>> > >>> #include <linux/security.h> > >>> #include <linux/init.h> > >>> +#include <linux/xattr.h> > >>> #include <linux/rculist.h> > >>> > >>> /** > >>> @@ -227,9 +228,11 @@ > >>> * @inode contains the inode structure of the newly created inode. > >>> * @dir contains the inode structure of the parent directory. > >>> * @qstr contains the last path component of the new object > >>> - * @name will be set to the allocated name suffix (e.g. selinux). > >>> - * @value will be set to the allocated attribute value. > >>> - * @len will be set to the length of the value. > >>> + * @xattrs contains the full array of xattrs allocated by LSMs where > >>> + * ->name will be set to the allocated name suffix (e.g. selinux). > >>> + * ->value will be set to the allocated attribute value. > >>> + * ->len will be set to the length of the value. > >>> + * @fs_data contains filesystem-specific data. > >>> * Returns 0 if @name and @value have been successfully set, > >>> * -EOPNOTSUPP if no security attribute is needed, or > >>> * -ENOMEM on memory allocation failure. > >>> @@ -1661,4 +1664,13 @@ static inline void security_delete_hooks(struct > >> security_hook_list *hooks, > >>> extern int lsm_inode_alloc(struct inode *inode); > >>> > >> Some "security researcher" with a fuzz tester is going to manage to dump > junk > >> into the slots and ruin your week. I suggest a simple change to make bounds > >> checking > >> possible. It should never happen, but if that was sufficient people would > >> love C > >> string processing better. > >> > >>> +static inline struct xattr *lsm_find_xattr_slot(struct xattr *xattrs) > >> +static inline struct xattr *lsm_find_xattr_slot(struct xattr *xattrs, > int available) > > Ok. I looked at how I should do that. Initially, I thought that I could > > use a global variable storing the number of inode_init_security > > implementations, determined at LSM registration time. Then, > > I realized that this would not work, as the number of array elements > > when security_old_inode_init_security() is called is 1. > > You can address that by expanding the call_int_hook MACRO in > security_old_inode_init_security() in place and change it to stop > after the first call. The two callers of security_old_inode_init_security() > are going to need to be converted to security_inode_init_security() > when the "complete" stacking (i.e. SELinux + Smack) anyway, so I don't > see that as an issue. The current version already does it. I was more concerned about LSMs requesting more than one slot. In this case, lsm_find_xattr_slot() could return a slot outside the array, unless we pass the correct size. If we convert ocfs2 and reiserfs to use security_inode_init_security(), we could use the global variable set at LSM registration time, and we don't need to add a new parameter. Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > Is anyone concerned that ocfs2 and reiserfs aren't EVM capable? > > > > > I modified the patch set to pass also the number of array elements. > > > > Roberto > > > > HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 > > Managing Director: Li Peng, Li Jian, Shi Yanli > > > >>> +{ > >>> + struct xattr *slot; > >>> + > >>> + for (slot = xattrs; slot && slot->name != NULL; slot++) > >> + for (slot = xattrs; slot && slot->name != NULL; slot++) > >> if (WARN_ON(slot > xattrs[available])) > >> return NULL; > >> > >>> + ; > >>> + > >>> + return slot; > >>> +} > >>> #endif /* ! __LINUX_LSM_HOOKS_H */ > >>> diff --git a/security/security.c b/security/security.c > >>> index 7f14e59c4f8e..2c1fe1496069 100644 > >>> --- a/security/security.c > >>> +++ b/security/security.c > >>> @@ -1037,18 +1037,16 @@ int security_inode_init_security(struct inode > >> *inode, struct inode *dir, > >>> if (!initxattrs) > >>> return call_int_hook(inode_init_security, -EOPNOTSUPP, > >> inode, > >>> - dir, qstr, NULL, NULL, NULL); > >>> + dir, qstr, NULL, fs_data); > >>> memset(new_xattrs, 0, sizeof(new_xattrs)); > >>> lsm_xattr = new_xattrs; > >>> ret = call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir, > qstr, > >>> - &lsm_xattr->name, > >>> - &lsm_xattr->value, > >>> - &lsm_xattr->value_len); > >>> + lsm_xattr, fs_data); > >>> if (ret) > >>> goto out; > >>> > >>> evm_xattr = lsm_xattr + 1; > >>> - ret = evm_inode_init_security(inode, lsm_xattr, evm_xattr); > >>> + ret = evm_inode_init_security(inode, new_xattrs, evm_xattr); > >>> if (ret) > >>> goto out; > >>> ret = initxattrs(inode, new_xattrs, fs_data); > >>> @@ -1071,10 +1069,13 @@ int security_old_inode_init_security(struct > inode > >> *inode, struct inode *dir, > >>> const struct qstr *qstr, const char **name, > >>> void **value, size_t *len) > >>> { > >>> + struct xattr xattr = { .name = NULL, .value = NULL, .value_len = 0 }; > >>> + struct xattr *lsm_xattr = (name && value && len) ? &xattr : NULL; > >>> + > >>> if (unlikely(IS_PRIVATE(inode))) > >>> return -EOPNOTSUPP; > >>> return call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir, > >>> - qstr, name, value, len); > >>> + qstr, lsm_xattr, NULL); > >>> } > >>> EXPORT_SYMBOL(security_old_inode_init_security); > >>> > >>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > >>> index ddd097790d47..806827eb132a 100644 > >>> --- a/security/selinux/hooks.c > >>> +++ b/security/selinux/hooks.c > >>> @@ -2916,11 +2916,11 @@ static int > selinux_dentry_create_files_as(struct > >> dentry *dentry, int mode, > >>> static int selinux_inode_init_security(struct inode *inode, struct inode > *dir, > >>> const struct qstr *qstr, > >>> - const char **name, > >>> - void **value, size_t *len) > >>> + struct xattr *xattrs, void *fs_data) > >>> { > >>> const struct task_security_struct *tsec = selinux_cred(current_cred()); > >>> struct superblock_security_struct *sbsec; > >>> + struct xattr *xattr = lsm_find_xattr_slot(xattrs); > >>> u32 newsid, clen; > >>> int rc; > >>> char *context; > >>> @@ -2947,16 +2947,15 @@ static int selinux_inode_init_security(struct > >> inode *inode, struct inode *dir, > >>> !(sbsec->flags & SBLABEL_MNT)) > >>> return -EOPNOTSUPP; > >>> > >>> - if (name) > >>> - *name = XATTR_SELINUX_SUFFIX; > >>> + if (xattr) { > >>> + xattr->name = XATTR_SELINUX_SUFFIX; > >>> > >>> - if (value && len) { > >>> rc = security_sid_to_context_force(&selinux_state, newsid, > >>> &context, &clen); > >>> if (rc) > >>> return rc; > >>> - *value = context; > >>> - *len = clen; > >>> + xattr->value = context; > >>> + xattr->value_len = clen; > >>> } > >>> > >>> return 0; > >>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c > >>> index 12a45e61c1a5..af7eee0fee52 100644 > >>> --- a/security/smack/smack_lsm.c > >>> +++ b/security/smack/smack_lsm.c > >>> @@ -962,26 +962,24 @@ static int smack_inode_alloc_security(struct > inode > >> *inode) > >>> * @inode: the newly created inode > >>> * @dir: containing directory object > >>> * @qstr: unused > >>> - * @name: where to put the attribute name > >>> - * @value: where to put the attribute value > >>> - * @len: where to put the length of the attribute > >>> + * @xattrs: where to put the attribute > >>> * > >>> * Returns 0 if it all works out, -ENOMEM if there's no memory > >>> */ > >>> static int smack_inode_init_security(struct inode *inode, struct inode > >> *dir, > >>> - const struct qstr *qstr, const char **name, > >>> - void **value, size_t *len) > >>> + const struct qstr *qstr, > >>> + struct xattr *xattrs, void *fs_data) > >>> { > >>> struct inode_smack *issp = smack_inode(inode); > >>> struct smack_known *skp = smk_of_current(); > >>> struct smack_known *isp = smk_of_inode(inode); > >>> struct smack_known *dsp = smk_of_inode(dir); > >>> + struct xattr *xattr = lsm_find_xattr_slot(xattrs); > >>> int may; > >>> > >>> - if (name) > >>> - *name = XATTR_SMACK_SUFFIX; > >>> + if (xattr) { > >>> + xattr->name = XATTR_SMACK_SUFFIX; > >>> > >>> - if (value && len) { > >>> rcu_read_lock(); > >>> may = smk_access_entry(skp->smk_known, dsp->smk_known, > >>> &skp->smk_rules); > >>> @@ -999,11 +997,11 @@ static int smack_inode_init_security(struct inode > >> *inode, struct inode *dir, > >>> issp->smk_flags |= SMK_INODE_CHANGED; > >>> } > >>> > >>> - *value = kstrdup(isp->smk_known, GFP_NOFS); > >>> - if (*value == NULL) > >>> + xattr->value = kstrdup(isp->smk_known, GFP_NOFS); > >>> + if (xattr->value == NULL) > >>> return -ENOMEM; > >>> > >>> - *len = strlen(isp->smk_known); > >>> + xattr->value_len = strlen(isp->smk_known); > >>> } > >>> > >>> return 0;
