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Date: Tue, 16 Jun 2015 16:36:52 +0800
From: lizf@...nel.org
To: stable@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Jann Horn <jann@...jh.net>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 158/172] fs: take i_mutex during prepare_binprm for set[ug]id executables
From: Jann Horn <jann@...jh.net>
3.4.108-rc1 review patch. If anyone has any objections, please let me know.
------------------
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@...jh.net>
Signed-off-by: Linus Torvalds <torvalds@...ux-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@...wei.com>
---
fs/exec.c | 65 +++++++++++++++++++++++++++++++++++++++------------------------
1 file changed, 40 insertions(+), 25 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 5b9dfbe..91d238f 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);
--
1.9.1
--
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