From 112b7147592e8f46bd1da4f961773e6d974f38a8 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Thu, 14 May 2020 12:53:44 -0500 Subject: [PATCH] exec: Convert security_bprm_set_creds into security_bprm_repopulate_creds Rename bprm->cap_elevated to bprm->active_secureexec and initialize it in prepare_binprm instead of in cap_bprm_set_creds. Initializing bprm->active_secureexec in prepare_binprm allows multiple implementations of security_bprm_repopulate_creds to play nicely with each other. Rename security_bprm_set_creds to security_bprm_reopulate_creds to emphasize that this path recomputes part of bprm->cred. This recomputation avoids the time of check vs time of use problems that are inherent in unix #! interpreters. In short two renames and a move in the location of initializing bprm->active_secureexec. Link: https://lkml.kernel.org/r/87o8qkzrxp.fsf_-_@x220.int.ebiederm.org Acked-by: Linus Torvalds Reviewed-by: Kees Cook Signed-off-by: "Eric W. Biederman" --- fs/exec.c | 8 ++++---- include/linux/binfmts.h | 4 ++-- include/linux/lsm_hook_defs.h | 2 +- include/linux/lsm_hooks.h | 4 ++-- include/linux/security.h | 8 ++++---- security/commoncap.c | 9 ++++----- security/security.c | 4 ++-- 7 files changed, 19 insertions(+), 20 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 9e70da47f8d9..8e3b93d51d31 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1366,7 +1366,7 @@ int begin_new_exec(struct linux_binprm * bprm) * the final state of setuid/setgid/fscaps can be merged into the * secureexec flag. */ - bprm->secureexec |= bprm->cap_elevated; + bprm->secureexec |= bprm->active_secureexec; if (bprm->secureexec) { /* Make sure parent cannot signal privileged process. */ @@ -1634,10 +1634,10 @@ int prepare_binprm(struct linux_binprm *bprm) int retval; loff_t pos = 0; + /* Recompute parts of bprm->cred based on bprm->file */ + bprm->active_secureexec = 0; bprm_fill_uid(bprm); - - /* fill in binprm security blob */ - retval = security_bprm_set_creds(bprm); + retval = security_bprm_repopulate_creds(bprm); if (retval) return retval; diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index d1217fcdedea..8605ab4a0f89 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -27,10 +27,10 @@ struct linux_binprm { unsigned long argmin; /* rlimit marker for copy_strings() */ unsigned int /* - * True if most recent call to cap_bprm_set_creds + * True if most recent call to security_bprm_set_creds * resulted in elevated privileges. */ - cap_elevated:1, + active_secureexec:1, /* * Set by bprm_creds_for_exec hook to indicate a * privilege-gaining exec has happened. Used to set diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index aab0695f41df..1e295ba12c0d 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -50,7 +50,7 @@ LSM_HOOK(int, 0, settime, const struct timespec64 *ts, const struct timezone *tz) LSM_HOOK(int, 0, vm_enough_memory, struct mm_struct *mm, long pages) LSM_HOOK(int, 0, bprm_creds_for_exec, struct linux_binprm *bprm) -LSM_HOOK(int, 0, bprm_set_creds, struct linux_binprm *bprm) +LSM_HOOK(int, 0, bprm_repopulate_creds, struct linux_binprm *bprm) LSM_HOOK(int, 0, bprm_check_security, struct linux_binprm *bprm) LSM_HOOK(void, LSM_RET_VOID, bprm_committing_creds, struct linux_binprm *bprm) LSM_HOOK(void, LSM_RET_VOID, bprm_committed_creds, struct linux_binprm *bprm) diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index c719af37df20..d618ecc4d660 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -44,7 +44,7 @@ * request libc enable secure mode. * @bprm contains the linux_binprm structure. * Return 0 if the hook is successful and permission is granted. - * @bprm_set_creds: + * @bprm_repopulate_creds: * Assuming that the relevant bits of @bprm->cred->security have been * previously set, examine @bprm->file and regenerate them. This is * so that the credentials derived from the interpreter the code is @@ -53,7 +53,7 @@ * reopen script, and may end up opening something completely different. * This hook may also optionally check permissions (e.g. for * transitions between security domains). - * The hook must set @bprm->cap_elevated to 1 if AT_SECURE should be set to + * The hook must set @bprm->active_secureexec to 1 if AT_SECURE should be set to * request libc enable secure mode. * @bprm contains the linux_binprm structure. * Return 0 if the hook is successful and permission is granted. diff --git a/include/linux/security.h b/include/linux/security.h index 1bd7a6582775..6dcec9375e8f 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -140,7 +140,7 @@ extern int cap_capset(struct cred *new, const struct cred *old, const kernel_cap_t *effective, const kernel_cap_t *inheritable, const kernel_cap_t *permitted); -extern int cap_bprm_set_creds(struct linux_binprm *bprm); +extern int cap_bprm_repopulate_creds(struct linux_binprm *bprm); extern int cap_inode_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags); extern int cap_inode_removexattr(struct dentry *dentry, const char *name); @@ -277,7 +277,7 @@ int security_syslog(int type); int security_settime64(const struct timespec64 *ts, const struct timezone *tz); int security_vm_enough_memory_mm(struct mm_struct *mm, long pages); int security_bprm_creds_for_exec(struct linux_binprm *bprm); -int security_bprm_set_creds(struct linux_binprm *bprm); +int security_bprm_repopulate_creds(struct linux_binprm *bprm); int security_bprm_check(struct linux_binprm *bprm); void security_bprm_committing_creds(struct linux_binprm *bprm); void security_bprm_committed_creds(struct linux_binprm *bprm); @@ -575,9 +575,9 @@ static inline int security_bprm_creds_for_exec(struct linux_binprm *bprm) return 0; } -static inline int security_bprm_set_creds(struct linux_binprm *bprm) +static inline int security_bprm_repopulate_creds(struct linux_binprm *bprm) { - return cap_bprm_set_creds(bprm); + return cap_bprm_repopulate_creds(bprm); } static inline int security_bprm_check(struct linux_binprm *bprm) diff --git a/security/commoncap.c b/security/commoncap.c index f4ee0ae106b2..045b5b80ea40 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -797,14 +797,14 @@ static inline bool nonroot_raised_pE(struct cred *new, const struct cred *old, } /** - * cap_bprm_set_creds - Set up the proposed credentials for execve(). + * cap_bprm_repopulate_creds - Set up the proposed credentials for execve(). * @bprm: The execution parameters, including the proposed creds * * Set up the proposed credentials for a new execution context being * constructed by execve(). The proposed creds in @bprm->cred is altered, * which won't take effect immediately. Returns 0 if successful, -ve on error. */ -int cap_bprm_set_creds(struct linux_binprm *bprm) +int cap_bprm_repopulate_creds(struct linux_binprm *bprm) { const struct cred *old = current_cred(); struct cred *new = bprm->cred; @@ -884,12 +884,11 @@ int cap_bprm_set_creds(struct linux_binprm *bprm) return -EPERM; /* Check for privilege-elevated exec. */ - bprm->cap_elevated = 0; if (is_setid || (!__is_real(root_uid, new) && (effective || __cap_grew(permitted, ambient, new)))) - bprm->cap_elevated = 1; + bprm->active_secureexec = 1; return 0; } @@ -1346,7 +1345,7 @@ static struct security_hook_list capability_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme), LSM_HOOK_INIT(capget, cap_capget), LSM_HOOK_INIT(capset, cap_capset), - LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds), + LSM_HOOK_INIT(bprm_repopulate_creds, cap_bprm_repopulate_creds), LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv), LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv), LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity), diff --git a/security/security.c b/security/security.c index 4ee76a729f73..b890b7e2a765 100644 --- a/security/security.c +++ b/security/security.c @@ -828,9 +828,9 @@ int security_bprm_creds_for_exec(struct linux_binprm *bprm) return call_int_hook(bprm_creds_for_exec, 0, bprm); } -int security_bprm_set_creds(struct linux_binprm *bprm) +int security_bprm_repopulate_creds(struct linux_binprm *bprm) { - return call_int_hook(bprm_set_creds, 0, bprm); + return call_int_hook(bprm_repopulate_creds, 0, bprm); } int security_bprm_check(struct linux_binprm *bprm)