[PATCH] setuid core dump
Add a new `suid_dumpable' sysctl:
This value can be used to query and set the core dump mode for setuid
or otherwise protected/tainted binaries. The modes are
0 - (default) - traditional behaviour. Any process which has changed
privilege levels or is execute only will not be dumped
1 - (debug) - all processes dump core when possible. The core dump is
owned by the current user and no security is applied. This is intended
for system debugging situations only. Ptrace is unchecked.
2 - (suidsafe) - any binary which normally would not be dumped is dumped
readable by root only. This allows the end user to remove such a dump but
not access it directly. For security reasons core dumps in this mode will
not overwrite one another or other files. This mode is appropriate when
adminstrators are attempting to debug problems in a normal environment.
(akpm:
> > +EXPORT_SYMBOL(suid_dumpable);
>
> EXPORT_SYMBOL_GPL?
No problem to me.
> > if (current->euid == current->uid && current->egid == current->gid)
> > current->mm->dumpable = 1;
>
> Should this be SUID_DUMP_USER?
Actually the feedback I had from last time was that the SUID_ defines
should go because its clearer to follow the numbers. They can go
everywhere (and there are lots of places where dumpable is tested/used
as a bool in untouched code)
> Maybe this should be renamed to `dump_policy' or something. Doing that
> would help us catch any code which isn't using the #defines, too.
Fair comment. The patch was designed to be easy to maintain for Red Hat
rather than for merging. Changing that field would create a gigantic
diff because it is used all over the place.
)
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 3515917..9f11d36 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -49,6 +49,7 @@
- shmmax [ sysv ipc ]
- shmmni
- stop-a [ SPARC only ]
+- suid_dumpable
- sysrq ==> Documentation/sysrq.txt
- tainted
- threads-max
@@ -300,6 +301,25 @@
==============================================================
+suid_dumpable:
+
+This value can be used to query and set the core dump mode for setuid
+or otherwise protected/tainted binaries. The modes are
+
+0 - (default) - traditional behaviour. Any process which has changed
+ privilege levels or is execute only will not be dumped
+1 - (debug) - all processes dump core when possible. The core dump is
+ owned by the current user and no security is applied. This is
+ intended for system debugging situations only. Ptrace is unchecked.
+2 - (suidsafe) - any binary which normally would not be dumped is dumped
+ readable by root only. This allows the end user to remove
+ such a dump but not access it directly. For security reasons
+ core dumps in this mode will not overwrite one another or
+ other files. This mode is appropriate when adminstrators are
+ attempting to debug problems in a normal environment.
+
+==============================================================
+
tainted:
Non-zero if the kernel has been tainted. Numeric values, which
diff --git a/fs/exec.c b/fs/exec.c
index 3a4b35a..4887191 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -58,6 +58,9 @@
int core_uses_pid;
char core_pattern[65] = "core";
+int suid_dumpable = 0;
+
+EXPORT_SYMBOL(suid_dumpable);
/* The maximal length of core_pattern is also specified in sysctl.c */
static struct linux_binfmt *formats;
@@ -864,6 +867,9 @@
if (current->euid == current->uid && current->egid == current->gid)
current->mm->dumpable = 1;
+ else
+ current->mm->dumpable = suid_dumpable;
+
name = bprm->filename;
/* Copies the binary name from after last slash */
@@ -884,7 +890,7 @@
permission(bprm->file->f_dentry->d_inode,MAY_READ, NULL) ||
(bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)) {
suid_keys(current);
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
}
/* An exec changes our domain. We are no longer part of the thread
@@ -1432,6 +1438,8 @@
struct inode * inode;
struct file * file;
int retval = 0;
+ int fsuid = current->fsuid;
+ int flag = 0;
binfmt = current->binfmt;
if (!binfmt || !binfmt->core_dump)
@@ -1441,6 +1449,16 @@
up_write(&mm->mmap_sem);
goto fail;
}
+
+ /*
+ * We cannot trust fsuid as being the "true" uid of the
+ * process nor do we know its entire history. We only know it
+ * was tainted so we dump it as root in mode 2.
+ */
+ if (mm->dumpable == 2) { /* Setuid core dump mode */
+ flag = O_EXCL; /* Stop rewrite attacks */
+ current->fsuid = 0; /* Dump root private */
+ }
mm->dumpable = 0;
init_completion(&mm->core_done);
spin_lock_irq(¤t->sighand->siglock);
@@ -1466,7 +1484,7 @@
lock_kernel();
format_corename(corename, core_pattern, signr);
unlock_kernel();
- file = filp_open(corename, O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE, 0600);
+ file = filp_open(corename, O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag, 0600);
if (IS_ERR(file))
goto fail_unlock;
inode = file->f_dentry->d_inode;
@@ -1491,6 +1509,7 @@
close_fail:
filp_close(file, NULL);
fail_unlock:
+ current->fsuid = fsuid;
complete_all(&mm->core_done);
fail:
return retval;
diff --git a/fs/proc/base.c b/fs/proc/base.c
index e31903a..ace151f 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -314,7 +314,7 @@
(current->gid != task->gid)) && !capable(CAP_SYS_PTRACE))
goto out;
rmb();
- if (!task->mm->dumpable && !capable(CAP_SYS_PTRACE))
+ if (task->mm->dumpable != 1 && !capable(CAP_SYS_PTRACE))
goto out;
if (security_ptrace(current, task))
goto out;
@@ -1113,7 +1113,9 @@
if (mm)
dumpable = mm->dumpable;
task_unlock(task);
- return dumpable;
+ if(dumpable == 1)
+ return 1;
+ return 0;
}
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 7e736e2..c1e82c5 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -69,6 +69,11 @@
extern int search_binary_handler(struct linux_binprm *,struct pt_regs *);
extern int flush_old_exec(struct linux_binprm * bprm);
+extern int suid_dumpable;
+#define SUID_DUMP_DISABLE 0 /* No setuid dumping */
+#define SUID_DUMP_USER 1 /* Dump as user of process */
+#define SUID_DUMP_ROOT 2 /* Dump as root */
+
/* Stack area protections */
#define EXSTACK_DEFAULT 0 /* Whatever the arch defaults to */
#define EXSTACK_DISABLE_X 1 /* Disable executable stacks */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b58afd9..901742f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -246,7 +246,7 @@
unsigned long saved_auxv[42]; /* for /proc/PID/auxv */
- unsigned dumpable:1;
+ unsigned dumpable:2;
cpumask_t cpu_vm_mask;
/* Architecture-specific MM context */
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index a17745c..614e939 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -136,6 +136,7 @@
KERN_UNKNOWN_NMI_PANIC=66, /* int: unknown nmi panic flag */
KERN_BOOTLOADER_TYPE=67, /* int: boot loader type */
KERN_RANDOMIZE=68, /* int: randomize virtual address space */
+ KERN_SETUID_DUMPABLE=69, /* int: behaviour of dumps for setuid core */
};
diff --git a/kernel/sys.c b/kernel/sys.c
index f006632..0a2c8cd 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -525,7 +525,7 @@
}
if (new_egid != old_egid)
{
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
if (rgid != (gid_t) -1 ||
@@ -556,7 +556,7 @@
{
if(old_egid != gid)
{
- current->mm->dumpable=0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
current->gid = current->egid = current->sgid = current->fsgid = gid;
@@ -565,7 +565,7 @@
{
if(old_egid != gid)
{
- current->mm->dumpable=0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
current->egid = current->fsgid = gid;
@@ -596,7 +596,7 @@
if(dumpclear)
{
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
current->uid = new_ruid;
@@ -653,7 +653,7 @@
if (new_euid != old_euid)
{
- current->mm->dumpable=0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
current->fsuid = current->euid = new_euid;
@@ -703,7 +703,7 @@
if (old_euid != uid)
{
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
current->fsuid = current->euid = uid;
@@ -748,7 +748,7 @@
if (euid != (uid_t) -1) {
if (euid != current->euid)
{
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
current->euid = euid;
@@ -798,7 +798,7 @@
if (egid != (gid_t) -1) {
if (egid != current->egid)
{
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
current->egid = egid;
@@ -845,7 +845,7 @@
{
if (uid != old_fsuid)
{
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
current->fsuid = uid;
@@ -875,7 +875,7 @@
{
if (gid != old_fsgid)
{
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
smp_wmb();
}
current->fsgid = gid;
@@ -1652,7 +1652,7 @@
error = 1;
break;
case PR_SET_DUMPABLE:
- if (arg2 != 0 && arg2 != 1) {
+ if (arg2 < 0 || arg2 > 2) {
error = -EINVAL;
break;
}
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 701d12c..24a4d12 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -58,6 +58,7 @@
extern int max_threads;
extern int sysrq_enabled;
extern int core_uses_pid;
+extern int suid_dumpable;
extern char core_pattern[];
extern int cad_pid;
extern int pid_max;
@@ -950,6 +951,14 @@
.proc_handler = &proc_dointvec,
},
#endif
+ {
+ .ctl_name = KERN_SETUID_DUMPABLE,
+ .procname = "suid_dumpable",
+ .data = &suid_dumpable,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
{ .ctl_name = 0 }
};
diff --git a/security/commoncap.c b/security/commoncap.c
index 849b8c3..04c12f5 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -149,7 +149,7 @@
if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
!cap_issubset (new_permitted, current->cap_permitted)) {
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
if (unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
if (!capable(CAP_SETUID)) {
diff --git a/security/dummy.c b/security/dummy.c
index b32eff1..6ff8875 100644
--- a/security/dummy.c
+++ b/security/dummy.c
@@ -130,7 +130,7 @@
static void dummy_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
{
if (bprm->e_uid != current->uid || bprm->e_gid != current->gid) {
- current->mm->dumpable = 0;
+ current->mm->dumpable = suid_dumpable;
if ((unsafe & ~LSM_UNSAFE_PTRACE_CAP) && !capable(CAP_SETUID)) {
bprm->e_uid = current->uid;
