[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>

1 files changed, 21 insertions, 2 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 3a4b35a14c0d..48871917d363 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 @@ int flush_old_exec(struct linux_binprm * bprm)
 
         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 @@ int flush_old_exec(struct linux_binprm * bprm)
             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 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
         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 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
                 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(&current->sighand->siglock);
@@ -1466,7 +1484,7 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
         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 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
 close_fail:
         filp_close(file, NULL);
 fail_unlock:
+        current->fsuid = fsuid;
         complete_all(&mm->core_done);
 fail:
         return retval;