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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: Thi=C3=A9baud Weksteen Reviewed-by: Stephen Smalley Tested-by: Stephen Smalley --- Changes since v2: - Add WARN_ON when using unexpected class. Return -EACCES instead=20 of -EPERM - Remove extra new line - Rebase on selinux/dev Changes since v1: - Move test of class earlier in selinux_bprm_creds_for_exec - Remove duplicate call to security_transition_sid Changes since RFC: - Remove enum argument, simply compare the anon inode name - Introduce a policy capability for compatility - Add validation of class in selinux_bprm_creds_for_exec include/linux/memfd.h | 2 ++ mm/memfd.c | 14 ++++++++++-- security/selinux/hooks.c | 26 +++++++++++++++++----- security/selinux/include/classmap.h | 2 ++ security/selinux/include/policycap.h | 1 + security/selinux/include/policycap_names.h | 1 + security/selinux/include/security.h | 5 +++++ 7 files changed, 44 insertions(+), 7 deletions(-) diff --git a/include/linux/memfd.h b/include/linux/memfd.h index 6f606d9573c3..cc74de3dbcfe 100644 --- a/include/linux/memfd.h +++ b/include/linux/memfd.h @@ -4,6 +4,8 @@ =20 #include =20 +#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 bbe679895ef6..63b439eb402a 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -433,6 +433,8 @@ static struct file *alloc_file(const char *name, unsign= ed int flags) { unsigned int *file_seals; struct file *file; + struct inode *inode; + int err =3D 0; =20 if (flags & MFD_HUGETLB) { file =3D hugetlb_file_setup(name, 0, VM_NORESERVE, @@ -444,12 +446,20 @@ static struct file *alloc_file(const char *name, unsi= gned int flags) } if (IS_ERR(file)) return file; + + inode =3D file_inode(file); + err =3D security_inode_init_security_anon(inode, + &QSTR(MEMFD_ANON_NAME), NULL); + if (err) { + fput(file); + file =3D ERR_PTR(err); + return file; + } + file->f_mode |=3D FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE; file->f_flags |=3D O_LARGEFILE; =20 if (flags & MFD_NOEXEC_SEAL) { - struct inode *inode =3D file_inode(file); - inode->i_mode &=3D ~0111; file_seals =3D memfd_file_seals_ptr(file); if (file_seals) { diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 0e47b4bb8d40..2b685f9dd61d 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -93,6 +93,7 @@ #include #include #include +#include =20 #include "avc.h" #include "objsec.h" @@ -2319,6 +2320,10 @@ static int selinux_bprm_creds_for_exec(struct linux_= binprm *bprm) new_tsec =3D selinux_cred(bprm->cred); isec =3D inode_security(inode); =20 + if (WARN_ON(isec->sclass !=3D SECCLASS_FILE && + isec->sclass !=3D SECCLASS_MEMFD_FILE)) + return -EACCES; + /* Default to the current task SID. */ new_tsec->sid =3D old_tsec->sid; new_tsec->osid =3D old_tsec->sid; @@ -2371,8 +2376,8 @@ static int selinux_bprm_creds_for_exec(struct linux_b= inprm *bprm) ad.u.file =3D bprm->file; =20 if (new_tsec->sid =3D=3D old_tsec->sid) { - rc =3D avc_has_perm(old_tsec->sid, isec->sid, - SECCLASS_FILE, FILE__EXECUTE_NO_TRANS, &ad); + rc =3D 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_b= inprm *bprm) if (rc) return rc; =20 - rc =3D avc_has_perm(new_tsec->sid, isec->sid, - SECCLASS_FILE, FILE__ENTRYPOINT, &ad); + rc =3D avc_has_perm(new_tsec->sid, isec->sid, isec->sclass, + FILE__ENTRYPOINT, &ad); if (rc) return rc; =20 @@ -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 =3D false; =20 if (unlikely(!selinux_initialized())) return 0; =20 + if (name !=3D NULL && name->name !=3D NULL && + !strcmp(name->name, MEMFD_ANON_NAME)) { + if (!selinux_policycap_memfd_class()) + return 0; + is_memfd =3D true; + } + isec =3D selinux_inode(inode); =20 /* @@ -3001,7 +3014,10 @@ static int selinux_inode_init_security_anon(struct i= node *inode, isec->sclass =3D context_isec->sclass; isec->sid =3D context_isec->sid; } else { - isec->sclass =3D SECCLASS_ANON_INODE; + if (is_memfd) + isec->sclass =3D SECCLASS_MEMFD_FILE; + else + isec->sclass =3D SECCLASS_ANON_INODE; rc =3D 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 5665aa5e7853..3ec85142771f 100644 --- a/security/selinux/include/classmap.h +++ b/security/selinux/include/classmap.h @@ -179,6 +179,8 @@ const struct security_class_mapping secclass_map[] =3D { { "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, {} } }; =20 diff --git a/security/selinux/include/policycap.h b/security/selinux/includ= e/policycap.h index 135a969f873c..231d02227e59 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 ff8882887651..454dab37bda3 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] =3D { "netif_wildcard", "genfs_seclabel_wildcard", "functionfs_seclabel", + "memfd_class", }; /* clang-format on */ =20 diff --git a/security/selinux/include/security.h b/security/selinux/include= /security.h index 0f954a40d3fc..5d1dad8058b1 100644 --- a/security/selinux/include/security.h +++ b/security/selinux/include/security.h @@ -209,6 +209,11 @@ static inline bool selinux_policycap_functionfs_seclab= el(void) selinux_state.policycap[POLICYDB_CAP_FUNCTIONFS_SECLABEL]); } =20 +static inline bool selinux_policycap_memfd_class(void) +{ + return READ_ONCE(selinux_state.policycap[POLICYDB_CAP_MEMFD_CLASS]); +} + struct selinux_policy_convert_data; =20 struct selinux_load_state { --=20 2.51.0.384.g4c02a37b29-goog