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author | Jann Horn <jann@thejh.net> | 2016-01-20 15:00:04 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-01-20 17:09:18 -0800 |
commit | caaee6234d05a58c5b4d05e7bf766131b810a657 (patch) | |
tree | 6227530109dd91ab5447fbd2211f09bc636845a7 /fs/proc/namespaces.c | |
parent | 3dfb7d8cdbc7ea0c2970450e60818bb3eefbad69 (diff) | |
download | linux-stable-caaee6234d05a58c5b4d05e7bf766131b810a657.tar.gz linux-stable-caaee6234d05a58c5b4d05e7bf766131b810a657.tar.bz2 linux-stable-caaee6234d05a58c5b4d05e7bf766131b810a657.zip |
ptrace: use fsuid, fsgid, effective creds for fs access checks
By checking the effective credentials instead of the real UID / permitted
capabilities, ensure that the calling process actually intended to use its
credentials.
To ensure that all ptrace checks use the correct caller credentials (e.g.
in case out-of-tree code or newly added code omits the PTRACE_MODE_*CREDS
flag), use two new flags and require one of them to be set.
The problem was that when a privileged task had temporarily dropped its
privileges, e.g. by calling setreuid(0, user_uid), with the intent to
perform following syscalls with the credentials of a user, it still passed
ptrace access checks that the user would not be able to pass.
While an attacker should not be able to convince the privileged task to
perform a ptrace() syscall, this is a problem because the ptrace access
check is reused for things in procfs.
In particular, the following somewhat interesting procfs entries only rely
on ptrace access checks:
/proc/$pid/stat - uses the check for determining whether pointers
should be visible, useful for bypassing ASLR
/proc/$pid/maps - also useful for bypassing ASLR
/proc/$pid/cwd - useful for gaining access to restricted
directories that contain files with lax permissions, e.g. in
this scenario:
lrwxrwxrwx root root /proc/13020/cwd -> /root/foobar
drwx------ root root /root
drwxr-xr-x root root /root/foobar
-rw-r--r-- root root /root/foobar/secret
Therefore, on a system where a root-owned mode 6755 binary changes its
effective credentials as described and then dumps a user-specified file,
this could be used by an attacker to reveal the memory layout of root's
processes or reveal the contents of files he is not allowed to access
(through /proc/$pid/cwd).
[akpm@linux-foundation.org: fix warning]
Signed-off-by: Jann Horn <jann@thejh.net>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Morris <james.l.morris@oracle.com>
Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/proc/namespaces.c')
-rw-r--r-- | fs/proc/namespaces.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c index 1dece8781f91..276f12431dbf 100644 --- a/fs/proc/namespaces.c +++ b/fs/proc/namespaces.c @@ -46,7 +46,7 @@ static const char *proc_ns_get_link(struct dentry *dentry, if (!task) return error; - if (ptrace_may_access(task, PTRACE_MODE_READ)) { + if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) { error = ns_get_path(&ns_path, task, ns_ops); if (!error) nd_jump_link(&ns_path); @@ -67,7 +67,7 @@ static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int bufl if (!task) return res; - if (ptrace_may_access(task, PTRACE_MODE_READ)) { + if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) { res = ns_get_name(name, sizeof(name), task, ns_ops); if (res >= 0) res = readlink_copy(buffer, buflen, name); |