coredump masking: reimplementation of dumpable using two flags
This patch changes mm_struct.dumpable to a pair of bit flags.
set_dumpable() converts three-value dumpable to two flags and stores it into
lower two bits of mm_struct.flags instead of mm_struct.dumpable.
get_dumpable() behaves in the opposite way.
[akpm@linux-foundation.org: export set_dumpable]
Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/exec.c b/fs/exec.c
index 498f2b3..7bdea79 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1058,9 +1058,9 @@
current->sas_ss_sp = current->sas_ss_size = 0;
if (current->euid == current->uid && current->egid == current->gid)
- current->mm->dumpable = 1;
+ set_dumpable(current->mm, 1);
else
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
name = bprm->filename;
@@ -1088,7 +1088,7 @@
file_permission(bprm->file, MAY_READ) ||
(bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)) {
suid_keys(current);
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
}
/* An exec changes our domain. We are no longer part of the thread
@@ -1665,6 +1665,56 @@
return core_waiters;
}
+/*
+ * set_dumpable converts traditional three-value dumpable to two flags and
+ * stores them into mm->flags. It modifies lower two bits of mm->flags, but
+ * these bits are not changed atomically. So get_dumpable can observe the
+ * intermediate state. To avoid doing unexpected behavior, get get_dumpable
+ * return either old dumpable or new one by paying attention to the order of
+ * modifying the bits.
+ *
+ * dumpable | mm->flags (binary)
+ * old new | initial interim final
+ * ---------+-----------------------
+ * 0 1 | 00 01 01
+ * 0 2 | 00 10(*) 11
+ * 1 0 | 01 00 00
+ * 1 2 | 01 11 11
+ * 2 0 | 11 10(*) 00
+ * 2 1 | 11 11 01
+ *
+ * (*) get_dumpable regards interim value of 10 as 11.
+ */
+void set_dumpable(struct mm_struct *mm, int value)
+{
+ switch (value) {
+ case 0:
+ clear_bit(MMF_DUMPABLE, &mm->flags);
+ smp_wmb();
+ clear_bit(MMF_DUMP_SECURELY, &mm->flags);
+ break;
+ case 1:
+ set_bit(MMF_DUMPABLE, &mm->flags);
+ smp_wmb();
+ clear_bit(MMF_DUMP_SECURELY, &mm->flags);
+ break;
+ case 2:
+ set_bit(MMF_DUMP_SECURELY, &mm->flags);
+ smp_wmb();
+ set_bit(MMF_DUMPABLE, &mm->flags);
+ break;
+ }
+}
+EXPORT_SYMBOL_GPL(set_dumpable);
+
+int get_dumpable(struct mm_struct *mm)
+{
+ int ret;
+
+ ret = mm->flags & 0x3;
+ return (ret >= 2) ? 2 : ret;
+}
+
int do_coredump(long signr, int exit_code, struct pt_regs * regs)
{
char corename[CORENAME_MAX_SIZE + 1];
@@ -1683,7 +1733,7 @@
if (!binfmt || !binfmt->core_dump)
goto fail;
down_write(&mm->mmap_sem);
- if (!mm->dumpable) {
+ if (!get_dumpable(mm)) {
up_write(&mm->mmap_sem);
goto fail;
}
@@ -1693,11 +1743,11 @@
* 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 */
+ if (get_dumpable(mm) == 2) { /* Setuid core dump mode */
flag = O_EXCL; /* Stop rewrite attacks */
current->fsuid = 0; /* Dump root private */
}
- mm->dumpable = 0;
+ set_dumpable(mm, 0);
retval = coredump_wait(exit_code);
if (retval < 0)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 42cb4f5..49b3ab0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1014,7 +1014,7 @@
task_lock(task);
mm = task->mm;
if (mm)
- dumpable = mm->dumpable;
+ dumpable = get_dumpable(mm);
task_unlock(task);
if(dumpable == 1)
return 1;
diff --git a/include/asm-ia64/processor.h b/include/asm-ia64/processor.h
index db81ba4..6251c76 100644
--- a/include/asm-ia64/processor.h
+++ b/include/asm-ia64/processor.h
@@ -295,9 +295,9 @@
regs->ar_bspstore = current->thread.rbs_bot; \
regs->ar_fpsr = FPSR_DEFAULT; \
regs->loadrs = 0; \
- regs->r8 = current->mm->dumpable; /* set "don't zap registers" flag */ \
+ regs->r8 = get_dumpable(current->mm); /* set "don't zap registers" flag */ \
regs->r12 = new_sp - 16; /* allocate 16 byte scratch area */ \
- if (unlikely(!current->mm->dumpable)) { \
+ if (unlikely(!get_dumpable(current->mm))) { \
/* \
* Zap scratch regs to avoid leaking bits between processes with different \
* uid/privileges. \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 731edaca..8dbd083 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -345,6 +345,13 @@
(mm)->hiwater_vm = (mm)->total_vm; \
} while (0)
+extern void set_dumpable(struct mm_struct *mm, int value);
+extern int get_dumpable(struct mm_struct *mm);
+
+/* mm flags */
+#define MMF_DUMPABLE 0 /* core dump is permitted */
+#define MMF_DUMP_SECURELY 1 /* core file is readable only by root */
+
struct mm_struct {
struct vm_area_struct * mmap; /* list of VMAs */
struct rb_root mm_rb;
@@ -402,7 +409,7 @@
unsigned int token_priority;
unsigned int last_interval;
- unsigned char dumpable:2;
+ unsigned long flags; /* Must use atomic bitops to access the bits */
/* coredumping support */
int core_waiters;
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 4a1745f1..82a558b 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -142,7 +142,7 @@
return -EPERM;
smp_rmb();
if (task->mm)
- dumpable = task->mm->dumpable;
+ dumpable = get_dumpable(task->mm);
if (!dumpable && !capable(CAP_SYS_PTRACE))
return -EPERM;
diff --git a/kernel/sys.c b/kernel/sys.c
index d40e40a..08562f4 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1036,7 +1036,7 @@
return -EPERM;
}
if (new_egid != old_egid) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
if (rgid != (gid_t) -1 ||
@@ -1066,13 +1066,13 @@
if (capable(CAP_SETGID)) {
if (old_egid != gid) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
current->gid = current->egid = current->sgid = current->fsgid = gid;
} else if ((gid == current->gid) || (gid == current->sgid)) {
if (old_egid != gid) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
current->egid = current->fsgid = gid;
@@ -1103,7 +1103,7 @@
switch_uid(new_user);
if (dumpclear) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
current->uid = new_ruid;
@@ -1159,7 +1159,7 @@
return -EAGAIN;
if (new_euid != old_euid) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
current->fsuid = current->euid = new_euid;
@@ -1209,7 +1209,7 @@
return -EPERM;
if (old_euid != uid) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
current->fsuid = current->euid = uid;
@@ -1254,7 +1254,7 @@
}
if (euid != (uid_t) -1) {
if (euid != current->euid) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
current->euid = euid;
@@ -1304,7 +1304,7 @@
}
if (egid != (gid_t) -1) {
if (egid != current->egid) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
current->egid = egid;
@@ -1350,7 +1350,7 @@
uid == current->suid || uid == current->fsuid ||
capable(CAP_SETUID)) {
if (uid != old_fsuid) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
current->fsuid = uid;
@@ -1379,7 +1379,7 @@
gid == current->sgid || gid == current->fsgid ||
capable(CAP_SETGID)) {
if (gid != old_fsgid) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
smp_wmb();
}
current->fsgid = gid;
@@ -2176,14 +2176,14 @@
error = put_user(current->pdeath_signal, (int __user *)arg2);
break;
case PR_GET_DUMPABLE:
- error = current->mm->dumpable;
+ error = get_dumpable(current->mm);
break;
case PR_SET_DUMPABLE:
if (arg2 < 0 || arg2 > 1) {
error = -EINVAL;
break;
}
- current->mm->dumpable = arg2;
+ set_dumpable(current->mm, arg2);
break;
case PR_SET_UNALIGN:
diff --git a/security/commoncap.c b/security/commoncap.c
index 384379e..338606e 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -148,7 +148,7 @@
if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
!cap_issubset (new_permitted, current->cap_permitted)) {
- current->mm->dumpable = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
if (unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
if (!capable(CAP_SETUID)) {
diff --git a/security/dummy.c b/security/dummy.c
index d6a112c..19d813d 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 = suid_dumpable;
+ set_dumpable(current->mm, suid_dumpable);
if ((unsafe & ~LSM_UNSAFE_PTRACE_CAP) && !capable(CAP_SETUID)) {
bprm->e_uid = current->uid;