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core dump: remain dumpable 

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.

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 check the core_waiters count as the means of
synchronization, which is sufficient.  Now we leave the "dumpable" bits alone.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Roland McGrath 2007-11-11 19:13:43 -08:00 committed by Linus Torvalds
parent 6e800af233
commit 00ec99da43
1 changed files with 4 additions and 2 deletions
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6
fs/exec.c
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@ -1692,7 +1692,10 @@ 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 another thread got here first, or we are not dumpable, bail out.
*/
if (mm->core_waiters || !get_dumpable(mm)) {
up_write(&mm->mmap_sem);
goto fail;
}
@ -1706,7 +1709,6 @@ 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)