On Wed, Jan 04, 2017 at 11:06:09AM +0100, gregkh@xxxxxxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxx> 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@xxxxxxx> > Date: Wed, 21 Dec 2016 16:26:24 +1100 > Subject: fs: exec: apply CLOEXEC before changing dumpable task flags > > From: Aleksa Sarai <asarai@xxxxxxx> > > 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@xxxxxxxxxxxxxxxxxx > Reported-by: Michael Crosby <crosbymichael@xxxxxxxxx> > Signed-off-by: Aleksa Sarai <asarai@xxxxxxx> > Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > --- > 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@xxxxxxx are > > queue-4.4/fs-exec-apply-cloexec-before-changing-dumpable-task-flags.patch > -- > To unsubscribe from this list: send the line "unsubscribe stable" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html