| Message ID | 1430133127-13796-5-git-send-email-luis.henriques@canonical.com |
|---|---|
| State | New |
| Headers | show |
On 04/27/2015 04:12 AM, Luis Henriques wrote: > From: Jann Horn <jann@thejh.net> > > This prevents a race between chown() and execve(), where chowning a > setuid-user binary to root would momentarily make the binary setuid > root. > > This patch was mostly written by Linus Torvalds. > > Signed-off-by: Jann Horn <jann@thejh.net> > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> > (cherry picked from commit 8b01fc86b9f425899f8a3a8fc1c47d73c2c20543) > CVE-2015-3339 > BugLink: https://bugs.launchpad.net/bugs/1447373 > Signed-off-by: Luis Henriques <luis.henriques@canonical.com> Acked-by: John Johansen <john.johansen@canonical.com> > --- > fs/exec.c | 76 ++++++++++++++++++++++++++++++++++++++++----------------------- > 1 file changed, 48 insertions(+), 28 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index f3f4a4e3b4fc..123d0bf19c17 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1263,6 +1263,53 @@ static void check_unsafe_exec(struct linux_binprm *bprm) > spin_unlock(&p->fs->lock); > } > > +static void bprm_fill_uid(struct linux_binprm *bprm) > +{ > + struct inode *inode; > + unsigned int mode; > + kuid_t uid; > + kgid_t gid; > + > + /* clear any previous set[ug]id data from a previous binary */ > + bprm->cred->euid = current_euid(); > + bprm->cred->egid = current_egid(); > + > + if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) > + return; > + > + if (task_no_new_privs(current)) > + return; > + > + inode = file_inode(bprm->file); > + mode = READ_ONCE(inode->i_mode); > + if (!(mode & (S_ISUID|S_ISGID))) > + return; > + > + /* Be careful if suid/sgid is set */ > + mutex_lock(&inode->i_mutex); > + > + /* reload atomically mode/uid/gid now that lock held */ > + mode = inode->i_mode; > + uid = inode->i_uid; > + gid = inode->i_gid; > + mutex_unlock(&inode->i_mutex); > + > + /* We ignore suid/sgid if there are no mappings for them in the ns */ > + if (!kuid_has_mapping(bprm->cred->user_ns, uid) || > + !kgid_has_mapping(bprm->cred->user_ns, gid)) > + return; > + > + if (mode & S_ISUID) { > + bprm->per_clear |= PER_CLEAR_ON_SETID; > + bprm->cred->euid = uid; > + } > + > + if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { > + bprm->per_clear |= PER_CLEAR_ON_SETID; > + bprm->cred->egid = gid; > + } > +} > + > /* > * Fill the binprm structure from the inode. > * Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes > @@ -1271,36 +1318,9 @@ static void check_unsafe_exec(struct linux_binprm *bprm) > */ > int prepare_binprm(struct linux_binprm *bprm) > { > - struct inode *inode = file_inode(bprm->file); > - umode_t mode = inode->i_mode; > int retval; > > - > - /* clear any previous set[ug]id data from a previous binary */ > - bprm->cred->euid = current_euid(); > - bprm->cred->egid = current_egid(); > - > - if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) && > - !task_no_new_privs(current) && > - kuid_has_mapping(bprm->cred->user_ns, inode->i_uid) && > - kgid_has_mapping(bprm->cred->user_ns, inode->i_gid)) { > - /* Set-uid? */ > - if (mode & S_ISUID) { > - bprm->per_clear |= PER_CLEAR_ON_SETID; > - bprm->cred->euid = inode->i_uid; > - } > - > - /* Set-gid? */ > - /* > - * If setgid is set but no group execute bit then this > - * is a candidate for mandatory locking, not a setgid > - * executable. > - */ > - if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { > - bprm->per_clear |= PER_CLEAR_ON_SETID; > - bprm->cred->egid = inode->i_gid; > - } > - } > + bprm_fill_uid(bprm); > > /* fill in binprm security blob */ > retval = security_bprm_set_creds(bprm); >
diff --git a/fs/exec.c b/fs/exec.c index f3f4a4e3b4fc..123d0bf19c17 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1263,6 +1263,53 @@ static void check_unsafe_exec(struct linux_binprm *bprm) spin_unlock(&p->fs->lock); } +static void bprm_fill_uid(struct linux_binprm *bprm) +{ + struct inode *inode; + unsigned int mode; + kuid_t uid; + kgid_t gid; + + /* clear any previous set[ug]id data from a previous binary */ + bprm->cred->euid = current_euid(); + bprm->cred->egid = current_egid(); + + if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) + return; + + if (task_no_new_privs(current)) + return; + + inode = file_inode(bprm->file); + mode = READ_ONCE(inode->i_mode); + if (!(mode & (S_ISUID|S_ISGID))) + return; + + /* Be careful if suid/sgid is set */ + mutex_lock(&inode->i_mutex); + + /* reload atomically mode/uid/gid now that lock held */ + mode = inode->i_mode; + uid = inode->i_uid; + gid = inode->i_gid; + mutex_unlock(&inode->i_mutex); + + /* We ignore suid/sgid if there are no mappings for them in the ns */ + if (!kuid_has_mapping(bprm->cred->user_ns, uid) || + !kgid_has_mapping(bprm->cred->user_ns, gid)) + return; + + if (mode & S_ISUID) { + bprm->per_clear |= PER_CLEAR_ON_SETID; + bprm->cred->euid = uid; + } + + if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { + bprm->per_clear |= PER_CLEAR_ON_SETID; + bprm->cred->egid = gid; + } +} + /* * Fill the binprm structure from the inode. * Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes @@ -1271,36 +1318,9 @@ static void check_unsafe_exec(struct linux_binprm *bprm) */ int prepare_binprm(struct linux_binprm *bprm) { - struct inode *inode = file_inode(bprm->file); - umode_t mode = inode->i_mode; int retval; - - /* clear any previous set[ug]id data from a previous binary */ - bprm->cred->euid = current_euid(); - bprm->cred->egid = current_egid(); - - if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) && - !task_no_new_privs(current) && - kuid_has_mapping(bprm->cred->user_ns, inode->i_uid) && - kgid_has_mapping(bprm->cred->user_ns, inode->i_gid)) { - /* Set-uid? */ - if (mode & S_ISUID) { - bprm->per_clear |= PER_CLEAR_ON_SETID; - bprm->cred->euid = inode->i_uid; - } - - /* Set-gid? */ - /* - * If setgid is set but no group execute bit then this - * is a candidate for mandatory locking, not a setgid - * executable. - */ - if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { - bprm->per_clear |= PER_CLEAR_ON_SETID; - bprm->cred->egid = inode->i_gid; - } - } + bprm_fill_uid(bprm); /* fill in binprm security blob */ retval = security_bprm_set_creds(bprm);