diff options
| -rw-r--r-- | fs/open.c | 38 |
1 files changed, 37 insertions, 1 deletions
diff --git a/fs/open.c b/fs/open.c index 8038cf652583..4401a73d4032 100644 --- a/fs/open.c +++ b/fs/open.c @@ -368,7 +368,37 @@ COMPAT_SYSCALL_DEFINE6(fallocate, int, fd, int, mode, compat_arg_u64_dual(offset * access() needs to use the real uid/gid, not the effective uid/gid. * We do this by temporarily clearing all FS-related capabilities and * switching the fsuid/fsgid around to the real ones. + * + * Creating new credentials is expensive, so we try to skip doing it, + * which we can if the result would match what we already got. */ +static bool access_need_override_creds(int flags) +{ + const struct cred *cred; + + if (flags & AT_EACCESS) + return false; + + cred = current_cred(); + if (!uid_eq(cred->fsuid, cred->uid) || + !gid_eq(cred->fsgid, cred->gid)) + return true; + + if (!issecure(SECURE_NO_SETUID_FIXUP)) { + kuid_t root_uid = make_kuid(cred->user_ns, 0); + if (!uid_eq(cred->uid, root_uid)) { + if (!cap_isclear(cred->cap_effective)) + return true; + } else { + if (!cap_isidentical(cred->cap_effective, + cred->cap_permitted)) + return true; + } + } + + return false; +} + static const struct cred *access_override_creds(void) { const struct cred *old_cred; @@ -378,6 +408,12 @@ static const struct cred *access_override_creds(void) if (!override_cred) return NULL; + /* + * XXX access_need_override_creds performs checks in hopes of skipping + * this work. Make sure it stays in sync if making any changes in this + * routine. + */ + override_cred->fsuid = override_cred->uid; override_cred->fsgid = override_cred->gid; @@ -437,7 +473,7 @@ static long do_faccessat(int dfd, const char __user *filename, int mode, int fla if (flags & AT_EMPTY_PATH) lookup_flags |= LOOKUP_EMPTY; - if (!(flags & AT_EACCESS)) { + if (access_need_override_creds(flags)) { old_cred = access_override_creds(); if (!old_cred) return -ENOMEM; |