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[PATCH] proc: Cleanup proc_fd_access_allowed

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In process of getting proc_fd_access_allowed to work it has developed a few
warts.  In particular the special case that always allows introspection and
the special case to allow inspection of kernel threads.

The special case for introspection is needed for /proc/self/mem.

The special case for kernel threads really should be overridable
by security modules.

So consolidate these checks into ptrace.c:may_attach().

The check to always allow introspection is trivial.

The check to allow access to kernel threads, and zombies is a little
trickier.  mem_read and mem_write already verify an mm exists so it isn't
needed twice.  proc_fd_access_allowed only doesn't want a check to verify
task->mm exits, s it prevents all access to kernel threads.  So just move
the task->mm check into ptrace_attach where it is needed for practical
reasons.

I did a quick audit and none of the security modules in the kernel seem to
care if they are passed a task without an mm into security_ptrace.  So the
above move should be safe and it allows security modules to come up with
more restrictive policy.

Signed-off-by: Eric W. Biederman <[email protected]>
Cc: Stephen Smalley <[email protected]>
Cc: Chris Wright <[email protected]>
Cc: James Morris <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Eric W. Biederman 2006-06-26 00:25:59 -07:00 • committed by Linus Torvalds
commit df26c40e56
2 changed files with 23 additions and 23 deletions
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20
kernel/ptrace.c
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@ -120,8 +120,18 @@ int ptrace_check_attach(struct task_struct *child, int kill)
static int may_attach(struct task_struct *task)
{
if (!task->mm)
return -EPERM;
/* May we inspect the given task?
* This check is used both for attaching with ptrace
* and for allowing access to sensitive information in /proc.
*
* ptrace_attach denies several cases that /proc allows
* because setting up the necessary parent/child relationship
* or halting the specified task is impossible.
*/
int dumpable = 0;
/* Don't let security modules deny introspection */
if (task == current)
return 0;
if (((current->uid != task->euid) ||
(current->uid != task->suid) ||
(current->uid != task->uid) ||
@ -130,7 +140,9 @@ static int may_attach(struct task_struct *task)
(current->gid != task->gid)) && !capable(CAP_SYS_PTRACE))
return -EPERM;
smp_rmb();
if (!task->mm->dumpable && !capable(CAP_SYS_PTRACE))
if (task->mm)
dumpable = task->mm->dumpable;
if (!dumpable && !capable(CAP_SYS_PTRACE))
return -EPERM;
return security_ptrace(current, task);
@ -176,6 +188,8 @@ repeat:
goto repeat;
}
if (!task->mm)
goto bad;
/* the same process cannot be attached many times */
if (task->ptrace & PT_PTRACED)
goto bad;