@@ -52,10 +52,18 @@
#define SECBIT_NO_CAP_AMBIENT_RAISE_LOCKED \
(issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE_LOCKED))
+/* When set, execve does not reset fsuid/fsgid to euid/egid */
+#define SECURE_KEEP_FSUID 8
+#define SECURE_KEEP_FSUID_LOCKED 9 /* make bit-8 immutable */
+
+#define SECBIT_KEEP_FSUID (issecure_mask(SECURE_KEEP_FSUID))
+#define SECBIT_KEEP_FSUID_LOCKED (issecure_mask(SECURE_KEEP_FSUID_LOCKED))
+
#define SECURE_ALL_BITS (issecure_mask(SECURE_NOROOT) | \
issecure_mask(SECURE_NO_SETUID_FIXUP) | \
issecure_mask(SECURE_KEEP_CAPS) | \
- issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE))
+ issecure_mask(SECURE_NO_CAP_AMBIENT_RAISE) | \
+ issecure_mask(SECURE_KEEP_FSUID))
#define SECURE_ALL_LOCKS (SECURE_ALL_BITS << 1)
#endif /* _UAPI_LINUX_SECUREBITS_H */
@@ -852,8 +852,13 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
old->cap_permitted);
}
- new->suid = new->fsuid = new->euid;
- new->sgid = new->fsgid = new->egid;
+ new->suid = new->euid;
+ new->sgid = new->egid;
+
+ if (!issecure(SECURE_KEEP_FSUID)) {
+ new->fsuid = new->euid;
+ new->fsgid = new->egid;
+ }
/* File caps or setid cancels ambient. */
if (has_fcap || is_setid)
Many kernel interfaces require real and/or effective root uid instead of relying solely of capabilities. An executable that uses such interfaces has to be set-uid-root or be executed by a thread with effective root uid. Presently, fsuid and saved uid will reset to the effective uid during execve. As a result, it is not possible to execute a binary such that it has effective root uid but retains fsuid/fsgid of the actual user. Retaining fsuid/fsgid of the actual user could be required if the executable needs to access the filesystem. It may also be desired from the security perspective of delegating the minimal set of privileges. Setting SECURE_KEEP_FSUID bit ensures that the current fsuid/fsgiud is retained by execve. Signed-off-by: Igor Lubashev <ilubashe@akamai.com> --- include/uapi/linux/securebits.h | 10 +++++++++- security/commoncap.c | 9 +++++++-- 2 files changed, 16 insertions(+), 3 deletions(-)