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https://github.com/Divested-Mobile/DivestOS-Build.git
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117 lines
3.2 KiB
Diff
117 lines
3.2 KiB
Diff
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From 470e517be17dd6ef8670bec7bd7831ea0d3ad8a6 Mon Sep 17 00:00:00 2001
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From: Jann Horn <jann@thejh.net>
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Date: Sun, 19 Apr 2015 02:48:39 +0200
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Subject: fs: take i_mutex during prepare_binprm for set[ug]id executables
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commit 8b01fc86b9f425899f8a3a8fc1c47d73c2c20543 upstream.
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This prevents a race between chown() and execve(), where chowning a
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setuid-user binary to root would momentarily make the binary setuid
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root.
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This patch was mostly written by Linus Torvalds.
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Signed-off-by: Jann Horn <jann@thejh.net>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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[bwh: Backported to 3.2:
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- Drop the task_no_new_privs() and user namespace checks
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- Open-code file_inode()
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- s/READ_ONCE/ACCESS_ONCE/
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- Adjust context]
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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---
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fs/exec.c | 65 +++++++++++++++++++++++++++++++++++++++------------------------
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1 file changed, 40 insertions(+), 25 deletions(-)
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diff --git a/fs/exec.c b/fs/exec.c
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index 78199eb..7adb43f 100644
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--- a/fs/exec.c
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+++ b/fs/exec.c
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@@ -1282,6 +1282,45 @@ int check_unsafe_exec(struct linux_binprm *bprm)
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return res;
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}
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+static void bprm_fill_uid(struct linux_binprm *bprm)
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+{
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+ struct inode *inode;
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+ unsigned int mode;
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+ uid_t uid;
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+ gid_t gid;
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+
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+ /* clear any previous set[ug]id data from a previous binary */
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+ bprm->cred->euid = current_euid();
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+ bprm->cred->egid = current_egid();
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+
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+ if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
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+ return;
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+
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+ inode = bprm->file->f_path.dentry->d_inode;
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+ mode = ACCESS_ONCE(inode->i_mode);
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+ if (!(mode & (S_ISUID|S_ISGID)))
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+ return;
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+
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+ /* Be careful if suid/sgid is set */
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+ mutex_lock(&inode->i_mutex);
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+
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+ /* reload atomically mode/uid/gid now that lock held */
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+ mode = inode->i_mode;
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+ uid = inode->i_uid;
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+ gid = inode->i_gid;
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+ mutex_unlock(&inode->i_mutex);
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+
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+ if (mode & S_ISUID) {
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+ bprm->per_clear |= PER_CLEAR_ON_SETID;
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+ bprm->cred->euid = uid;
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+ }
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+
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+ if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
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+ bprm->per_clear |= PER_CLEAR_ON_SETID;
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+ bprm->cred->egid = gid;
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+ }
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+}
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+
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/*
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* Fill the binprm structure from the inode.
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* Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes
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@@ -1290,36 +1329,12 @@ int check_unsafe_exec(struct linux_binprm *bprm)
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*/
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int prepare_binprm(struct linux_binprm *bprm)
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{
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- umode_t mode;
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- struct inode * inode = bprm->file->f_path.dentry->d_inode;
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int retval;
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- mode = inode->i_mode;
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if (bprm->file->f_op == NULL)
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return -EACCES;
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- /* clear any previous set[ug]id data from a previous binary */
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- bprm->cred->euid = current_euid();
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- bprm->cred->egid = current_egid();
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-
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- if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)) {
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- /* Set-uid? */
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- if (mode & S_ISUID) {
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- bprm->per_clear |= PER_CLEAR_ON_SETID;
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- bprm->cred->euid = inode->i_uid;
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- }
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-
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- /* Set-gid? */
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- /*
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- * If setgid is set but no group execute bit then this
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- * is a candidate for mandatory locking, not a setgid
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- * executable.
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- */
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- if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
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- bprm->per_clear |= PER_CLEAR_ON_SETID;
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- bprm->cred->egid = inode->i_gid;
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- }
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- }
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+ bprm_fill_uid(bprm);
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/* fill in binprm security blob */
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retval = security_bprm_set_creds(bprm);
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--
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cgit v1.1
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