2.6.32-longterm review patch. If anyone has any objections, please let me know.
------------------
From: Jann Horn <j...@thejh.net>
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 <j...@thejh.net>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
[bwh: Backported to 3.2:
- Drop the task_no_new_privs() and user namespace checks
- Open-code file_inode()
- s/READ_ONCE/ACCESS_ONCE/
- Adjust context]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
(cherry picked from commit 470e517be17dd6ef8670bec7bd7831ea0d3ad8a6)
Signed-off-by: Willy Tarreau <w...@1wt.eu>
---
fs/exec.c | 65 +++++++++++++++++++++++++++++++++++++++------------------------
1 file changed, 40 insertions(+), 25 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index c32ae34..8dc1270 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1181,6 +1181,45 @@ int check_unsafe_exec(struct linux_binprm *bprm)
return res;
}
+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;
+ }
+}
+
/*
* Fill the binprm structure from the inode.
* Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes
@@ -1189,36 +1228,12 @@ 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);
--
1.7.12.2.21.g234cd45.dirty
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