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author | Aleksa Sarai <asarai@suse.de> | 2016-12-21 08:26:24 +0300 |
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committer | Al Viro <viro@zeniv.linux.org.uk> | 2016-12-23 07:03:41 +0300 |
commit | 613cc2b6f272c1a8ad33aefa21cad77af23139f7 (patch) | |
tree | 145d05796d97e0d2f5919880fe32597cbf0d72e0 /fs/nilfs2/sysfs.c | |
parent | e522751d605d99a81508e58390a8f51ee96fb662 (diff) | |
download | linux-613cc2b6f272c1a8ad33aefa21cad77af23139f7.tar.xz |
fs: exec: apply CLOEXEC before changing dumpable task flags
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
Cc: <stable@vger.kernel.org> # v3.2+
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>
Diffstat (limited to 'fs/nilfs2/sysfs.c')
0 files changed, 0 insertions, 0 deletions