The patch titled Subject: kernel/sys.c: fix and improve control flow in __sys_setres[ug]id() has been added to the -mm mm-nonmm-unstable branch. Its filename is kernel-sysc-fix-and-improve-control-flow-in-__sys_setresid.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-nonmm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Ondrej Mosnacek omosnace@redhat.com Subject: kernel/sys.c: fix and improve control flow in __sys_setres[ug]id() Date: Fri, 17 Feb 2023 17:21:54 +0100
Linux Security Modules (LSMs) that implement the "capable" hook will usually emit an access denial message to the audit log whenever they "block" the current task from using the given capability based on their security policy.
The occurrence of a denial is used as an indication that the given task has attempted an operation that requires the given access permission, so the callers of functions that perform LSM permission checks must take care to avoid calling them too early (before it is decided if the permission is actually needed to perform the requested operation).
The __sys_setres[ug]id() functions violate this convention by first calling ns_capable_setid() and only then checking if the operation requires the capability or not. It means that any caller that has the capability granted by DAC (task's capability set) but not by MAC (LSMs) will generate a "denied" audit record, even if is doing an operation for which the capability is not required.
Fix this by reordering the checks such that ns_capable_setid() is checked last and -EPERM is returned immediately if it returns false.
While there, also do two small optimizations: * move the capability check before prepare_creds() and * bail out early in case of a no-op.
Link: https://lkml.kernel.org/r/20230217162154.837549-1-omosnace@redhat.com Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Ondrej Mosnacek omosnace@redhat.com Cc: Eric W. Biederman ebiederm@xmission.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
--- a/kernel/sys.c~kernel-sysc-fix-and-improve-control-flow-in-__sys_setresid +++ a/kernel/sys.c @@ -665,6 +665,7 @@ long __sys_setresuid(uid_t ruid, uid_t e struct cred *new; int retval; kuid_t kruid, keuid, ksuid; + bool ruid_new, euid_new, suid_new;
kruid = make_kuid(ns, ruid); keuid = make_kuid(ns, euid); @@ -679,25 +680,29 @@ long __sys_setresuid(uid_t ruid, uid_t e if ((suid != (uid_t) -1) && !uid_valid(ksuid)) return -EINVAL;
+ old = current_cred(); + + /* check for no-op */ + if ((ruid == (uid_t) -1 || uid_eq(kruid, old->uid)) && + (euid == (uid_t) -1 || (uid_eq(keuid, old->euid) && + uid_eq(keuid, old->fsuid))) && + (suid == (uid_t) -1 || uid_eq(ksuid, old->suid))) + return 0; + + ruid_new = ruid != (uid_t) -1 && !uid_eq(kruid, old->uid) && + !uid_eq(kruid, old->euid) && !uid_eq(kruid, old->suid); + euid_new = euid != (uid_t) -1 && !uid_eq(keuid, old->uid) && + !uid_eq(keuid, old->euid) && !uid_eq(keuid, old->suid); + suid_new = suid != (uid_t) -1 && !uid_eq(ksuid, old->uid) && + !uid_eq(ksuid, old->euid) && !uid_eq(ksuid, old->suid); + if ((ruid_new || euid_new || suid_new) && + !ns_capable_setid(old->user_ns, CAP_SETUID)) + return -EPERM; + new = prepare_creds(); if (!new) return -ENOMEM;
- old = current_cred(); - - retval = -EPERM; - if (!ns_capable_setid(old->user_ns, CAP_SETUID)) { - if (ruid != (uid_t) -1 && !uid_eq(kruid, old->uid) && - !uid_eq(kruid, old->euid) && !uid_eq(kruid, old->suid)) - goto error; - if (euid != (uid_t) -1 && !uid_eq(keuid, old->uid) && - !uid_eq(keuid, old->euid) && !uid_eq(keuid, old->suid)) - goto error; - if (suid != (uid_t) -1 && !uid_eq(ksuid, old->uid) && - !uid_eq(ksuid, old->euid) && !uid_eq(ksuid, old->suid)) - goto error; - } - if (ruid != (uid_t) -1) { new->uid = kruid; if (!uid_eq(kruid, old->uid)) { @@ -762,6 +767,7 @@ long __sys_setresgid(gid_t rgid, gid_t e struct cred *new; int retval; kgid_t krgid, kegid, ksgid; + bool rgid_new, egid_new, sgid_new;
krgid = make_kgid(ns, rgid); kegid = make_kgid(ns, egid); @@ -774,23 +780,28 @@ long __sys_setresgid(gid_t rgid, gid_t e if ((sgid != (gid_t) -1) && !gid_valid(ksgid)) return -EINVAL;
+ old = current_cred(); + + /* check for no-op */ + if ((rgid == (gid_t) -1 || gid_eq(krgid, old->gid)) && + (egid == (gid_t) -1 || (gid_eq(kegid, old->egid) && + gid_eq(kegid, old->fsgid))) && + (sgid == (gid_t) -1 || gid_eq(ksgid, old->sgid))) + return 0; + + rgid_new = rgid != (gid_t) -1 && !gid_eq(krgid, old->gid) && + !gid_eq(krgid, old->egid) && !gid_eq(krgid, old->sgid); + egid_new = egid != (gid_t) -1 && !gid_eq(kegid, old->gid) && + !gid_eq(kegid, old->egid) && !gid_eq(kegid, old->sgid); + sgid_new = sgid != (gid_t) -1 && !gid_eq(ksgid, old->gid) && + !gid_eq(ksgid, old->egid) && !gid_eq(ksgid, old->sgid); + if ((rgid_new || egid_new || sgid_new) && + !ns_capable_setid(old->user_ns, CAP_SETGID)) + return -EPERM; + new = prepare_creds(); if (!new) return -ENOMEM; - old = current_cred(); - - retval = -EPERM; - if (!ns_capable_setid(old->user_ns, CAP_SETGID)) { - if (rgid != (gid_t) -1 && !gid_eq(krgid, old->gid) && - !gid_eq(krgid, old->egid) && !gid_eq(krgid, old->sgid)) - goto error; - if (egid != (gid_t) -1 && !gid_eq(kegid, old->gid) && - !gid_eq(kegid, old->egid) && !gid_eq(kegid, old->sgid)) - goto error; - if (sgid != (gid_t) -1 && !gid_eq(ksgid, old->gid) && - !gid_eq(ksgid, old->egid) && !gid_eq(ksgid, old->sgid)) - goto error; - }
if (rgid != (gid_t) -1) new->gid = krgid; _
Patches currently in -mm which might be from omosnace@redhat.com are
kernel-sysc-fix-and-improve-control-flow-in-__sys_setresid.patch