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authorEric W. Biederman <ebiederm@xmission.com>2020-05-29 22:00:54 -0500
committerEric W. Biederman <ebiederm@xmission.com>2020-05-29 22:00:54 -0500
commit56305aa9b6fab91a5555a45796b79c1b0a6353d1 (patch)
tree378ea4452668d448b0834fd08008a5f81619f1fd /security
parenta7868323c2638a7c6c5b30b37831b73cbdf0dc15 (diff)
exec: Compute file based creds only once
Move the computation of creds from prepare_binfmt into begin_new_exec so that the creds need only be computed once. This is just code reorganization no semantic changes of any kind are made. Moving the computation is safe. I have looked through the kernel and verified none of the binfmts look at bprm->cred directly, and that there are no helpers that look at bprm->cred indirectly. Which means that it is not a problem to compute the bprm->cred later in the execution flow as it is not used until it becomes current->cred. A new function bprm_creds_from_file is added to contain the work that needs to be done. bprm_creds_from_file first computes which file bprm->executable or most likely bprm->file that the bprm->creds will be computed from. The funciton bprm_fill_uid is updated to receive the file instead of accessing bprm->file. The now unnecessary work needed to reset the bprm->cred->euid, and bprm->cred->egid is removed from brpm_fill_uid. A small comment to document that bprm_fill_uid now only deals with the work to handle suid and sgid files. The default case is already heandled by prepare_exec_creds. The function security_bprm_repopulate_creds is renamed security_bprm_creds_from_file and now is explicitly passed the file from which to compute the creds. The documentation of the bprm_creds_from_file security hook is updated to explain when the hook is called and what it needs to do. The file is passed from cap_bprm_creds_from_file into get_file_caps so that the caps are computed for the appropriate file. The now unnecessary work in cap_bprm_creds_from_file to reset the ambient capabilites has been removed. A small comment to document that the work of cap_bprm_creds_from_file is to read capabilities from the files secureity attribute and derive capabilities from the fact the user had uid 0 has been added. Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'security')
-rw-r--r--security/commoncap.c24
-rw-r--r--security/security.c4
2 files changed, 15 insertions, 13 deletions
diff --git a/security/commoncap.c b/security/commoncap.c
index 6de72d22dc6c..59bf3c1674c8 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -647,7 +647,8 @@ int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data
* its xattrs and, if present, apply them to the proposed credentials being
* constructed by execve().
*/
-static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_fcap)
+static int get_file_caps(struct linux_binprm *bprm, struct file *file,
+ bool *effective, bool *has_fcap)
{
int rc = 0;
struct cpu_vfs_cap_data vcaps;
@@ -657,7 +658,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_f
if (!file_caps_enabled)
return 0;
- if (!mnt_may_suid(bprm->file->f_path.mnt))
+ if (!mnt_may_suid(file->f_path.mnt))
return 0;
/*
@@ -665,10 +666,10 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_f
* explicit that capability bits are limited to s_user_ns and its
* descendants.
*/
- if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns))
+ if (!current_in_userns(file->f_path.mnt->mnt_sb->s_user_ns))
return 0;
- rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
+ rc = get_vfs_caps_from_disk(file->f_path.dentry, &vcaps);
if (rc < 0) {
if (rc == -EINVAL)
printk(KERN_NOTICE "Invalid argument reading file caps for %s\n",
@@ -797,26 +798,27 @@ static inline bool nonroot_raised_pE(struct cred *new, const struct cred *old,
}
/**
- * cap_bprm_repopulate_creds - Set up the proposed credentials for execve().
+ * cap_bprm_creds_from_file - Set up the proposed credentials for execve().
* @bprm: The execution parameters, including the proposed creds
+ * @file: The file to pull the credentials from
*
* 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_repopulate_creds(struct linux_binprm *bprm)
+int cap_bprm_creds_from_file(struct linux_binprm *bprm, struct file *file)
{
+ /* Process setpcap binaries and capabilities for uid 0 */
const struct cred *old = current_cred();
struct cred *new = bprm->cred;
bool effective = false, has_fcap = false, is_setid;
int ret;
kuid_t root_uid;
- new->cap_ambient = old->cap_ambient;
if (WARN_ON(!cap_ambient_invariant_ok(old)))
return -EPERM;
- ret = get_file_caps(bprm, &effective, &has_fcap);
+ ret = get_file_caps(bprm, file, &effective, &has_fcap);
if (ret < 0)
return ret;
@@ -826,7 +828,7 @@ int cap_bprm_repopulate_creds(struct linux_binprm *bprm)
/* if we have fs caps, clear dangerous personality flags */
if (__cap_gained(permitted, new, old))
- bprm->pf_per_clear |= PER_CLEAR_ON_SETID;
+ bprm->per_clear |= PER_CLEAR_ON_SETID;
/* Don't let someone trace a set[ug]id/setpcap binary with the revised
* credentials unless they have the appropriate permit.
@@ -889,7 +891,7 @@ int cap_bprm_repopulate_creds(struct linux_binprm *bprm)
(!__is_real(root_uid, new) &&
(effective ||
__cap_grew(permitted, ambient, new))))
- bprm->active_secureexec = 1;
+ bprm->secureexec = 1;
return 0;
}
@@ -1346,7 +1348,7 @@ 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_repopulate_creds, cap_bprm_repopulate_creds),
+ LSM_HOOK_INIT(bprm_creds_from_file, cap_bprm_creds_from_file),
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 b890b7e2a765..259b8e750aa2 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_repopulate_creds(struct linux_binprm *bprm)
+int security_bprm_creds_from_file(struct linux_binprm *bprm, struct file *file)
{
- return call_int_hook(bprm_repopulate_creds, 0, bprm);
+ return call_int_hook(bprm_creds_from_file, 0, bprm, file);
}
int security_bprm_check(struct linux_binprm *bprm)