From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Stephane Eranian <eranian@google.com>
Subject: perfmon trouble
Date: Mon, 11 Jun 2018 03:10:29 +0100 [thread overview]
Message-ID: <20180611021028.GT30522@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20180609155107.GH30522@ZenIV.linux.org.uk>
On Sat, Jun 09, 2018 at 04:51:08PM +0100, Al Viro wrote:
> Stephane, could you comment on the situation in there? I realize that you
> hadn't touched that thing in more than a decade, but I've no idea who else
> might be familiar with that thing and it's very inconveniently special...
Having looked through that code... ouch. It tries to have munmap-on-close,
of all things. Which has interesting consequences; consider, for example,
fd = perfctl(-1, PFM_CREATE_CONTEXT, &blah, 1); // create a context
....
pid = fork();
if (!pid) {
execve("/usr/bin/something_suid", ...);
...
}
with something_suid(8) doing an explicit "close each descriptor past stdout"
loop.
PFM_CREATE_CONTEXT has created a context, mmapped its buffer (and stored
the address of that mapping in ctx->ctx_smpl_vaddr) and, having opened
an associated file, sticks it into descriptor table and returns the descriptor.
On fork/exec we have
* descriptor table copied to child
* all mappings copied to child and then destroyed by execve
* execve ends up with the new binary (and libraries, etc.) mmapped
(in child)
Now, our careful suid-root binary does close(2) on its copy of descriptor.
pfm_flush() is called. ctx->task != current, so we proceed to
/*
* remove virtual mapping, if any, for the calling task.
* cannot reset ctx field until last user is calling close().
*
* ctx_smpl_vaddr must never be cleared because it is needed
* by every task with access to the context
*
* When called from do_exit(), the mm context is gone already, therefore
* mm is NULL, i.e., the VMA is already gone and we do not have to
* do anything here
*/
if (ctx->ctx_smpl_vaddr && current->mm) {
smpl_buf_vaddr = ctx->ctx_smpl_vaddr;
smpl_buf_size = ctx->ctx_smpl_size;
}
UNPROTECT_CTX(ctx, flags);
/*
* if there was a mapping, then we systematically remove it
* at this point. Cannot be done inside critical section
* because some VM function reenables interrupts.
*
*/
if (smpl_buf_vaddr) pfm_remove_smpl_mapping(smpl_buf_vaddr, smpl_buf_size);
... with the last call doing vm_munmap() on the area in question. In the
address space of that suid-root binary, taking out whatever *it* had mapped
at that address range...
I wouldn't be surprised if that turned out to be realistically exploitable ;-/
Is there any documentation of that thing's semantics? perfmonctl(2) doesn't
mention the mapping at all and link to HP site in the arch/ia64/kernel/perfmon.c
is 404-compliant. Playing with archive.org brings a sourceforget reference,
but I hadn't been able to find anything ia64-related docs in there...
next prev parent reply other threads:[~2018-06-11 2:10 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-08 18:48 [RFC][PATCHES] getting rid of int *open in ->atomic_open() and friends Al Viro
2018-06-08 18:50 ` [PATCH 01/13] drm_mode_create_lease_ioctl(): switch to filp_clone_open() Al Viro
2018-06-08 18:50 ` [PATCH 02/13] rename filp_clone_open() to file_clone_open() Al Viro
2018-06-08 18:50 ` [PATCH 03/13] introduce FMODE_OPENED Al Viro
2018-06-08 18:50 ` [PATCH 04/13] get rid of 'opened' argument of finish_open() Al Viro
2018-06-08 18:50 ` [PATCH 05/13] pull fput() on late failures into path_openat() Al Viro
2018-06-08 18:50 ` [PATCH 06/13] switch all remaining checks for FILE_OPENED to FMODE_OPENED Al Viro
2018-06-08 18:50 ` [PATCH 07/13] now we can fold open_check_o_direct() into do_dentry_open() Al Viro
2018-06-08 18:50 ` [PATCH 08/13] __gfs2_lookup(), nfs_finish_open() and fuse_create_open() don't need 'opened' Al Viro
2018-06-08 18:50 ` [PATCH 09/13] introduce FMODE_CREATED and switch to it Al Viro
2018-06-08 18:50 ` [PATCH 10/13] IMA: don't propagate opened through the entire thing Al Viro
2018-06-08 18:50 ` [PATCH 11/13] gfs2_create_inode() doesn't need 'opened' anymore Al Viro
2018-06-08 18:50 ` [PATCH 12/13] get rid of 'opened' argument of ->atomic_open() Al Viro
2018-06-08 18:50 ` [PATCH 13/13] get rid of 'opened' in path_openat() and the helpers downstream Al Viro
2018-06-08 18:57 ` [RFC][PATCHES] getting rid of int *open in ->atomic_open() and friends Linus Torvalds
2018-06-09 5:10 ` Al Viro
2018-06-09 15:51 ` Al Viro
2018-06-11 2:10 ` Al Viro [this message]
2018-06-11 16:23 ` perfmon trouble Christoph Hellwig
2018-06-11 16:48 ` Matthew Wilcox
2018-06-11 17:04 ` Linus Torvalds
2018-06-11 17:18 ` Matthew Wilcox
2018-06-11 18:51 ` Stephane Eranian
2018-06-11 18:59 ` Linus Torvalds
2018-06-11 20:06 ` Al Viro
2018-06-17 18:22 ` [RFC][PATCHES] getting rid of int *open in ->atomic_open() and friends Al Viro
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