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author | Aleksa Sarai <asarai@suse.de> | 2016-12-21 16:26:24 +1100 |
---|---|---|
committer | Ben Hutchings <ben@decadent.org.uk> | 2017-03-16 02:26:38 +0000 |
commit | 8f7ceb94581c9bc3f91f5ef29e3efc3a67de0b57 (patch) | |
tree | b62fb4186325cfe2b222a404727796969dde7ad1 /fs | |
parent | 12d4dffb0d8b11d946e4077c672c544a7e1673c0 (diff) | |
download | linux-stable-8f7ceb94581c9bc3f91f5ef29e3efc3a67de0b57.tar.gz linux-stable-8f7ceb94581c9bc3f91f5ef29e3efc3a67de0b57.tar.bz2 linux-stable-8f7ceb94581c9bc3f91f5ef29e3efc3a67de0b57.zip |
fs: exec: apply CLOEXEC before changing dumpable task flags
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: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/exec.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/fs/exec.c b/fs/exec.c index 993ed0aba99a..5b653a126b20 100644 --- 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> @@ -1087,6 +1087,13 @@ int flush_old_exec(struct linux_binprm * bprm) 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: @@ -1136,7 +1143,6 @@ void setup_new_exec(struct linux_binprm * bprm) group */ current->self_exec_id++; flush_signal_handlers(current, 0); - do_close_on_exec(current->files); } EXPORT_SYMBOL(setup_new_exec); |