Messages in this thread Patch in this message | | | From | Roland McGrath <> | Subject | [PATCH] core dump: remain dumpable | Date | Wed, 10 Oct 2007 23:27:30 -0700 (PDT) |
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The coredump code always calls set_dumpable(0) when it starts (even if RLIMIT_CORE prevents any core from being dumped). The effect of this (via task_dumpable) is to make /proc/pid/* files owned by root instead of the user, so the user can no longer examine his own process--in a case where there was never any privileged data to protect. This affects e.g. auxv, environ, fd; in Fedora (execshield) kernels, also maps. In practice, you can only notice this when a debugger has requested PTRACE_EVENT_EXIT tracing.
As far as I know, set_dumpable was only used in do_coredump for synchronization and not intended for any security purpose. (It doesn't secure anything that wasn't already unsecured when a process dies by SIGTERM instead of SIGQUIT.)
This changes do_coredump to use a separate bit for its synchronization, so the "dumpable" bits remain the same.
Signed-off-by: Roland McGrath <roland@redhat.com> --- fs/exec.c | 4 ++-- include/linux/sched.h | 2 ++ 2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c index 073b0b8..7f1e355 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1727,7 +1727,8 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs) if (!binfmt || !binfmt->core_dump) goto fail; down_write(&mm->mmap_sem); - if (!get_dumpable(mm)) { + if (!get_dumpable(mm) || + test_and_set_bit(MMF_DUMP_STARTED, &mm->flags)) { up_write(&mm->mmap_sem); goto fail; } @@ -1741,7 +1742,6 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs) flag = O_EXCL; /* Stop rewrite attacks */ current->fsuid = 0; /* Dump root private */ } - set_dumpable(mm, 0); retval = coredump_wait(exit_code); if (retval < 0) diff --git a/include/linux/sched.h b/include/linux/sched.h index 1f274c2..33676ad 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -367,6 +367,8 @@ extern int get_dumpable(struct mm_struct *mm); #define MMF_DUMP_FILTER_DEFAULT \ ((1 << MMF_DUMP_ANON_PRIVATE) | (1 << MMF_DUMP_ANON_SHARED)) +#define MMF_DUMP_STARTED 16 /* some thread entered do_coredump already */ + struct mm_struct { struct vm_area_struct * mmap; /* list of VMAs */ struct rb_root mm_rb; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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