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ptrace: Check PTRACE_O_SUSPEND_SECCOMP permission on PTRACE_SEIZE

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Setting PTRACE_O_SUSPEND_SECCOMP is supposed to be a highly privileged
operation because it allows the tracee to completely bypass all seccomp
filters on kernels with CONFIG_CHECKPOINT_RESTORE=y. It is only supposed to
be settable by a process with global CAP_SYS_ADMIN, and only if that
process is not subject to any seccomp filters at all.

However, while these permission checks were done on the PTRACE_SETOPTIONS
path, they were missing on the PTRACE_SEIZE path, which also sets
user-specified ptrace flags.

Move the permissions checks out into a helper function and let both
ptrace_attach() and ptrace_setoptions() call it.

Cc: stable@kernel.org
Fixes: 13c4a90119 ("seccomp: add ptrace options for suspend/resume")
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lkml.kernel.org/r/20220319010838.1386861-1-jannh@google.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Jann Horn 2022-03-19 02:08:37 +01:00 committed by Eric W. Biederman
parent 6487d1dab8
commit ee1fee9005
1 changed files with 32 additions and 15 deletions
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47
kernel/ptrace.c
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@ -371,6 +371,26 @@ bool ptrace_may_access(struct task_struct *task, unsigned int mode)
return !err;
}
static int check_ptrace_options(unsigned long data)
{
if (data & ~(unsigned long)PTRACE_O_MASK)
return -EINVAL;
if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) {
if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) ||
!IS_ENABLED(CONFIG_SECCOMP))
return -EINVAL;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (seccomp_mode(&current->seccomp) != SECCOMP_MODE_DISABLED ||
current->ptrace & PT_SUSPEND_SECCOMP)
return -EPERM;
}
return 0;
}
static int ptrace_attach(struct task_struct *task, long request,
unsigned long addr,
unsigned long flags)
@ -382,8 +402,16 @@ static int ptrace_attach(struct task_struct *task, long request,
if (seize) {
if (addr != 0)
goto out;
/*
* This duplicates the check in check_ptrace_options() because
* ptrace_attach() and ptrace_setoptions() have historically
* used different error codes for unknown ptrace options.
*/
if (flags & ~(unsigned long)PTRACE_O_MASK)
goto out;
retval = check_ptrace_options(flags);
if (retval)
return retval;
flags = PT_PTRACED | PT_SEIZED | (flags << PT_OPT_FLAG_SHIFT);
} else {
flags = PT_PTRACED;
@ -654,22 +682,11 @@ int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long ds
static int ptrace_setoptions(struct task_struct *child, unsigned long data)
{
unsigned flags;
int ret;
if (data & ~(unsigned long)PTRACE_O_MASK)
return -EINVAL;
if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) {
if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) ||
!IS_ENABLED(CONFIG_SECCOMP))
return -EINVAL;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (seccomp_mode(&current->seccomp) != SECCOMP_MODE_DISABLED ||
current->ptrace & PT_SUSPEND_SECCOMP)
return -EPERM;
}
ret = check_ptrace_options(data);
if (ret)
return ret;
/* Avoid intermediate state when all opts are cleared */
flags = child->ptrace;