From: Thiébaud Weksteen Date: Thu, 18 Sep 2025 02:04:34 +0000 (+1000) Subject: memfd,selinux: call security_inode_init_security_anon() X-Git-Tag: v6.19-rc1~190^2~3 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=094e94d13b606b820e3d1383e3a361f680ff023a;p=thirdparty%2Fkernel%2Flinux.git memfd,selinux: call security_inode_init_security_anon() Prior to this change, no security hooks were called at the creation of a memfd file. It means that, for SELinux as an example, it will receive the default type of the filesystem that backs the in-memory inode. In most cases, that would be tmpfs, but if MFD_HUGETLB is passed, it will be hugetlbfs. Both can be considered implementation details of memfd. It also means that it is not possible to differentiate between a file coming from memfd_create and a file coming from a standard tmpfs mount point. Additionally, no permission is validated at creation, which differs from the similar memfd_secret syscall. Call security_inode_init_security_anon during creation. This ensures that the file is setup similarly to other anonymous inodes. On SELinux, it means that the file will receive the security context of its task. The ability to limit fexecve on memfd has been of interest to avoid potential pitfalls where /proc/self/exe or similar would be executed [1][2]. Reuse the "execute_no_trans" and "entrypoint" access vectors, similarly to the file class. These access vectors may not make sense for the existing "anon_inode" class. Therefore, define and assign a new class "memfd_file" to support such access vectors. Guard these changes behind a new policy capability named "memfd_class". [1] https://crbug.com/1305267 [2] https://lore.kernel.org/lkml/20221215001205.51969-1-jeffxu@google.com/ Signed-off-by: Thiébaud Weksteen Reviewed-by: Stephen Smalley Tested-by: Stephen Smalley Acked-by: Hugh Dickins [PM: subj tweak] Signed-off-by: Paul Moore --- diff --git a/include/linux/memfd.h b/include/linux/memfd.h index 6f606d9573c38..cc74de3dbcfe9 100644 --- a/include/linux/memfd.h +++ b/include/linux/memfd.h @@ -4,6 +4,8 @@ #include +#define MEMFD_ANON_NAME "[memfd]" + #ifdef CONFIG_MEMFD_CREATE extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg); struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx); diff --git a/mm/memfd.c b/mm/memfd.c index 1d109c1acf211..a61acbe5ded3b 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -433,6 +433,8 @@ static struct file *alloc_file(const char *name, unsigned int flags) { unsigned int *file_seals; struct file *file; + struct inode *inode; + int err = 0; if (flags & MFD_HUGETLB) { file = hugetlb_file_setup(name, 0, VM_NORESERVE, @@ -444,12 +446,20 @@ static struct file *alloc_file(const char *name, unsigned int flags) } if (IS_ERR(file)) return file; + + inode = file_inode(file); + err = security_inode_init_security_anon(inode, + &QSTR(MEMFD_ANON_NAME), NULL); + if (err) { + fput(file); + file = ERR_PTR(err); + return file; + } + file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE; file->f_flags |= O_LARGEFILE; if (flags & MFD_NOEXEC_SEAL) { - struct inode *inode = file_inode(file); - inode->i_mode &= ~0111; file_seals = memfd_file_seals_ptr(file); if (file_seals) { diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index dfc22da42f307..a22b1920242f2 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -93,6 +93,7 @@ #include #include #include +#include #include "avc.h" #include "objsec.h" @@ -2319,6 +2320,10 @@ static int selinux_bprm_creds_for_exec(struct linux_binprm *bprm) new_tsec = selinux_cred(bprm->cred); isec = inode_security(inode); + if (WARN_ON(isec->sclass != SECCLASS_FILE && + isec->sclass != SECCLASS_MEMFD_FILE)) + return -EACCES; + /* Default to the current task SID. */ new_tsec->sid = old_tsec->sid; new_tsec->osid = old_tsec->sid; @@ -2371,8 +2376,8 @@ static int selinux_bprm_creds_for_exec(struct linux_binprm *bprm) ad.u.file = bprm->file; if (new_tsec->sid == old_tsec->sid) { - rc = avc_has_perm(old_tsec->sid, isec->sid, - SECCLASS_FILE, FILE__EXECUTE_NO_TRANS, &ad); + rc = avc_has_perm(old_tsec->sid, isec->sid, isec->sclass, + FILE__EXECUTE_NO_TRANS, &ad); if (rc) return rc; } else { @@ -2382,8 +2387,8 @@ static int selinux_bprm_creds_for_exec(struct linux_binprm *bprm) if (rc) return rc; - rc = avc_has_perm(new_tsec->sid, isec->sid, - SECCLASS_FILE, FILE__ENTRYPOINT, &ad); + rc = avc_has_perm(new_tsec->sid, isec->sid, isec->sclass, + FILE__ENTRYPOINT, &ad); if (rc) return rc; @@ -2978,10 +2983,18 @@ static int selinux_inode_init_security_anon(struct inode *inode, struct common_audit_data ad; struct inode_security_struct *isec; int rc; + bool is_memfd = false; if (unlikely(!selinux_initialized())) return 0; + if (name != NULL && name->name != NULL && + !strcmp(name->name, MEMFD_ANON_NAME)) { + if (!selinux_policycap_memfd_class()) + return 0; + is_memfd = true; + } + isec = selinux_inode(inode); /* @@ -3001,7 +3014,10 @@ static int selinux_inode_init_security_anon(struct inode *inode, isec->sclass = context_isec->sclass; isec->sid = context_isec->sid; } else { - isec->sclass = SECCLASS_ANON_INODE; + if (is_memfd) + isec->sclass = SECCLASS_MEMFD_FILE; + else + isec->sclass = SECCLASS_ANON_INODE; rc = security_transition_sid( sid, sid, isec->sclass, name, &isec->sid); diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h index 5665aa5e7853e..3ec85142771fc 100644 --- a/security/selinux/include/classmap.h +++ b/security/selinux/include/classmap.h @@ -179,6 +179,8 @@ const struct security_class_mapping secclass_map[] = { { "anon_inode", { COMMON_FILE_PERMS, NULL } }, { "io_uring", { "override_creds", "sqpoll", "cmd", "allowed", NULL } }, { "user_namespace", { "create", NULL } }, + { "memfd_file", + { COMMON_FILE_PERMS, "execute_no_trans", "entrypoint", NULL } }, /* last one */ { NULL, {} } }; diff --git a/security/selinux/include/policycap.h b/security/selinux/include/policycap.h index 135a969f873ca..231d02227e593 100644 --- a/security/selinux/include/policycap.h +++ b/security/selinux/include/policycap.h @@ -18,6 +18,7 @@ enum { POLICYDB_CAP_NETIF_WILDCARD, POLICYDB_CAP_GENFS_SECLABEL_WILDCARD, POLICYDB_CAP_FUNCTIONFS_SECLABEL, + POLICYDB_CAP_MEMFD_CLASS, __POLICYDB_CAP_MAX }; #define POLICYDB_CAP_MAX (__POLICYDB_CAP_MAX - 1) diff --git a/security/selinux/include/policycap_names.h b/security/selinux/include/policycap_names.h index ff88828876517..454dab37bda3f 100644 --- a/security/selinux/include/policycap_names.h +++ b/security/selinux/include/policycap_names.h @@ -21,6 +21,7 @@ const char *const selinux_policycap_names[__POLICYDB_CAP_MAX] = { "netif_wildcard", "genfs_seclabel_wildcard", "functionfs_seclabel", + "memfd_class", }; /* clang-format on */ diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h index 0f954a40d3fc7..5d1dad8058b14 100644 --- a/security/selinux/include/security.h +++ b/security/selinux/include/security.h @@ -209,6 +209,11 @@ static inline bool selinux_policycap_functionfs_seclabel(void) selinux_state.policycap[POLICYDB_CAP_FUNCTIONFS_SECLABEL]); } +static inline bool selinux_policycap_memfd_class(void) +{ + return READ_ONCE(selinux_state.policycap[POLICYDB_CAP_MEMFD_CLASS]); +} + struct selinux_policy_convert_data; struct selinux_load_state {