* Patch "fs: exec: apply CLOEXEC before changing dumpable task flags" has been added to the 4.4-stable tree
@ 2017-01-04 10:06 gregkh
2017-01-04 10:15 ` Greg KH
0 siblings, 1 reply; 3+ messages in thread
From: gregkh @ 2017-01-04 10:06 UTC (permalink / raw)
To: asarai, crosbymichael, gregkh, viro; +Cc: stable, stable-commits
This is a note to let you know that I've just added the patch titled
fs: exec: apply CLOEXEC before changing dumpable task flags
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fs-exec-apply-cloexec-before-changing-dumpable-task-flags.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.
>From 613cc2b6f272c1a8ad33aefa21cad77af23139f7 Mon Sep 17 00:00:00 2001
From: Aleksa Sarai <asarai@suse.de>
Date: Wed, 21 Dec 2016 16:26:24 +1100
Subject: fs: exec: apply CLOEXEC before changing dumpable task flags
From: Aleksa Sarai <asarai@suse.de>
commit 613cc2b6f272c1a8ad33aefa21cad77af23139f7 upstream.
If you have a process that has set itself to be non-dumpable, and it
then undergoes exec(2), any CLOEXEC file descriptors it has open are
"exposed" during a race window between the dumpable flags of the process
being reset for exec(2) and CLOEXEC being applied to the file
descriptors. This can be exploited by a process by attempting to access
/proc/<pid>/fd/... during this window, without requiring CAP_SYS_PTRACE.
The race in question is after set_dumpable has been (for get_link,
though the trace is basically the same for readlink):
[vfs]
-> proc_pid_link_inode_operations.get_link
-> proc_pid_get_link
-> proc_fd_access_allowed
-> ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
Which will return 0, during the race window and CLOEXEC file descriptors
will still be open during this window because do_close_on_exec has not
been called yet. As a result, the ordering of these calls should be
reversed to avoid this race window.
This is of particular concern to container runtimes, where joining a
PID namespace with file descriptors referring to the host filesystem
can result in security issues (since PRCTL_SET_DUMPABLE doesn't protect
against access of CLOEXEC file descriptors -- file descriptors which may
reference filesystem objects the container shouldn't have access to).
Cc: dev@opencontainers.org
Reported-by: Michael Crosby <crosbymichael@gmail.com>
Signed-off-by: Aleksa Sarai <asarai@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/exec.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -19,7 +19,7 @@
* current->executable is only used by the procfs. This allows a dispatch
* table to check for several different types of binary formats. We keep
* trying until we recognize the file or we run out of supported binary
- * formats.
+ * formats.
*/
#include <linux/slab.h>
@@ -1114,6 +1114,13 @@ int flush_old_exec(struct linux_binprm *
flush_thread();
current->personality &= ~bprm->per_clear;
+ /*
+ * We have to apply CLOEXEC before we change whether the process is
+ * dumpable (in setup_new_exec) to avoid a race with a process in userspace
+ * trying to access the should-be-closed file descriptors of a process
+ * undergoing exec(2).
+ */
+ do_close_on_exec(current->files);
return 0;
out:
@@ -1176,7 +1183,6 @@ void setup_new_exec(struct linux_binprm
group */
current->self_exec_id++;
flush_signal_handlers(current, 0);
- do_close_on_exec(current->files);
}
EXPORT_SYMBOL(setup_new_exec);
Patches currently in stable-queue which might be from asarai@suse.de are
queue-4.4/fs-exec-apply-cloexec-before-changing-dumpable-task-flags.patch
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Patch "fs: exec: apply CLOEXEC before changing dumpable task flags" has been added to the 4.4-stable tree
2017-01-04 10:06 Patch "fs: exec: apply CLOEXEC before changing dumpable task flags" has been added to the 4.4-stable tree gregkh
@ 2017-01-04 10:15 ` Greg KH
2017-01-04 10:34 ` Greg KH
0 siblings, 1 reply; 3+ messages in thread
From: Greg KH @ 2017-01-04 10:15 UTC (permalink / raw)
To: asarai, crosbymichael, viro; +Cc: stable, stable-commits
On Wed, Jan 04, 2017 at 11:06:09AM +0100, gregkh@linuxfoundation.org wrote:
>
> This is a note to let you know that I've just added the patch titled
>
> fs: exec: apply CLOEXEC before changing dumpable task flags
>
> to the 4.4-stable tree which can be found at:
> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>
> The filename of the patch is:
> fs-exec-apply-cloexec-before-changing-dumpable-task-flags.patch
> and it can be found in the queue-4.4 subdirectory.
>
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.
Oops, no, this version breaks the build, I had to drop it...
greg k-h
>
>
> >From 613cc2b6f272c1a8ad33aefa21cad77af23139f7 Mon Sep 17 00:00:00 2001
> From: Aleksa Sarai <asarai@suse.de>
> Date: Wed, 21 Dec 2016 16:26:24 +1100
> Subject: fs: exec: apply CLOEXEC before changing dumpable task flags
>
> From: Aleksa Sarai <asarai@suse.de>
>
> commit 613cc2b6f272c1a8ad33aefa21cad77af23139f7 upstream.
>
> If you have a process that has set itself to be non-dumpable, and it
> then undergoes exec(2), any CLOEXEC file descriptors it has open are
> "exposed" during a race window between the dumpable flags of the process
> being reset for exec(2) and CLOEXEC being applied to the file
> descriptors. This can be exploited by a process by attempting to access
> /proc/<pid>/fd/... during this window, without requiring CAP_SYS_PTRACE.
>
> The race in question is after set_dumpable has been (for get_link,
> though the trace is basically the same for readlink):
>
> [vfs]
> -> proc_pid_link_inode_operations.get_link
> -> proc_pid_get_link
> -> proc_fd_access_allowed
> -> ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
>
> Which will return 0, during the race window and CLOEXEC file descriptors
> will still be open during this window because do_close_on_exec has not
> been called yet. As a result, the ordering of these calls should be
> reversed to avoid this race window.
>
> This is of particular concern to container runtimes, where joining a
> PID namespace with file descriptors referring to the host filesystem
> can result in security issues (since PRCTL_SET_DUMPABLE doesn't protect
> against access of CLOEXEC file descriptors -- file descriptors which may
> reference filesystem objects the container shouldn't have access to).
>
> Cc: dev@opencontainers.org
> Reported-by: Michael Crosby <crosbymichael@gmail.com>
> Signed-off-by: Aleksa Sarai <asarai@suse.de>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
> fs/exec.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -19,7 +19,7 @@
> * current->executable is only used by the procfs. This allows a dispatch
> * table to check for several different types of binary formats. We keep
> * trying until we recognize the file or we run out of supported binary
> - * formats.
> + * formats.
> */
>
> #include <linux/slab.h>
> @@ -1114,6 +1114,13 @@ int flush_old_exec(struct linux_binprm *
> flush_thread();
> current->personality &= ~bprm->per_clear;
>
> + /*
> + * We have to apply CLOEXEC before we change whether the process is
> + * dumpable (in setup_new_exec) to avoid a race with a process in userspace
> + * trying to access the should-be-closed file descriptors of a process
> + * undergoing exec(2).
> + */
> + do_close_on_exec(current->files);
> return 0;
>
> out:
> @@ -1176,7 +1183,6 @@ void setup_new_exec(struct linux_binprm
> group */
> current->self_exec_id++;
> flush_signal_handlers(current, 0);
> - do_close_on_exec(current->files);
> }
> EXPORT_SYMBOL(setup_new_exec);
>
>
>
> Patches currently in stable-queue which might be from asarai@suse.de are
>
> queue-4.4/fs-exec-apply-cloexec-before-changing-dumpable-task-flags.patch
> --
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Patch "fs: exec: apply CLOEXEC before changing dumpable task flags" has been added to the 4.4-stable tree
2017-01-04 10:15 ` Greg KH
@ 2017-01-04 10:34 ` Greg KH
0 siblings, 0 replies; 3+ messages in thread
From: Greg KH @ 2017-01-04 10:34 UTC (permalink / raw)
To: asarai, crosbymichael, viro; +Cc: stable, stable-commits
On Wed, Jan 04, 2017 at 11:15:04AM +0100, Greg KH wrote:
> On Wed, Jan 04, 2017 at 11:06:09AM +0100, gregkh@linuxfoundation.org wrote:
> >
> > This is a note to let you know that I've just added the patch titled
> >
> > fs: exec: apply CLOEXEC before changing dumpable task flags
> >
> > to the 4.4-stable tree which can be found at:
> > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> >
> > The filename of the patch is:
> > fs-exec-apply-cloexec-before-changing-dumpable-task-flags.patch
> > and it can be found in the queue-4.4 subdirectory.
> >
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@vger.kernel.org> know about it.
>
> Oops, no, this version breaks the build, I had to drop it...
Sorry for the false alarm, this patch is fine, I brought it back, it was
a different patch breaking the 4.4 build.
greg k-h
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-01-04 10:06 Patch "fs: exec: apply CLOEXEC before changing dumpable task flags" has been added to the 4.4-stable tree gregkh
2017-01-04 10:15 ` Greg KH
2017-01-04 10:34 ` Greg KH
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