diff options
author | Jann Horn <jann@thejh.net> | 2015-04-19 02:48:39 +0200 |
---|---|---|
committer | Zefan Li <lizefan@huawei.com> | 2015-06-19 11:40:33 +0800 |
commit | e661bb1c6d22a28c9038f4c2888e1e3b52f5b247 (patch) | |
tree | e797ebe2ad53fc979ec9c94eb628a222c42a102e | |
parent | fcafa22d451873a00bc97caa3abeeaa07b07685e (diff) |
fs: take i_mutex during prepare_binprm for set[ug]id executables
commit 8b01fc86b9f425899f8a3a8fc1c47d73c2c20543 upstream.
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>
[lizf: Backported to 3.4:
- adjust context
- remove task_no_new_priv and user namespace stuff
- open-code file_inode()
- s/READ_ONCE/ACCESS_ONCE]
Signed-off-by: Zefan Li <lizefan@huawei.com>
-rw-r--r-- | fs/exec.c | 65 |
1 files changed, 40 insertions, 25 deletions
diff --git a/fs/exec.c b/fs/exec.c index 5b9dfbe84b19..91d238fd1ea2 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1248,6 +1248,45 @@ void install_exec_creds(struct linux_binprm *bprm) } EXPORT_SYMBOL(install_exec_creds); +static void bprm_fill_uid(struct linux_binprm *bprm) +{ + struct inode *inode; + unsigned int mode; + uid_t uid; + gid_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; + + inode = bprm->file->f_path.dentry->d_inode; + mode = ACCESS_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); + + 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; + } +} + /* * determine how safe it is to execute the proposed program * - the caller must hold ->cred_guard_mutex to protect against @@ -1297,36 +1336,12 @@ static int check_unsafe_exec(struct linux_binprm *bprm) */ int prepare_binprm(struct linux_binprm *bprm) { - umode_t mode; - struct inode * inode = bprm->file->f_path.dentry->d_inode; int retval; - mode = inode->i_mode; if (bprm->file->f_op == NULL) return -EACCES; - /* 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)) { - /* 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); |