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)