1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
|
Date: Sun, 19 Apr 2015 02:48:39 +0200
Subject: fs: take i_mutex during prepare_binprm for set[ug]id executables
[ Upstream commit 8b01fc86b9f425899f8a3a8fc1c47d73c2c20543 ]
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.
Fixes CVE-2015-3339.
Upstream-Status: Backport
Signed-off-by: Jann Horn <jann@thejh.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Sona Sarmadi <sona.sarmadi@enea.com>
---
fs/exec.c | 76 ++++++++++++++++++++++++++++++++++++++++-----------------------
1 file changed, 48 insertions(+), 28 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 7302b75..2e83209 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1250,6 +1250,53 @@ 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
@@ -1258,36 +1305,9 @@ 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);
--
cgit v0.11.2
|
