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author | Ingo Molnar <mingo@kernel.org> | 2015-09-30 15:59:17 +0200 |
---|---|---|
committer | Luis Henriques <luis.henriques@canonical.com> | 2015-12-13 17:49:51 +0000 |
commit | a9ba345c1aecd2b912762ad9d5c2432e3fbf1968 (patch) | |
tree | 32e5b81dbf71dbd9fd59658524a711e5550a7d44 | |
parent | b83c9091f46af02ffc6b2fffdb641f5cf71b7ee8 (diff) | |
download | linux-stable-a9ba345c1aecd2b912762ad9d5c2432e3fbf1968.tar.gz linux-stable-a9ba345c1aecd2b912762ad9d5c2432e3fbf1968.tar.bz2 linux-stable-a9ba345c1aecd2b912762ad9d5c2432e3fbf1968.zip |
fs/proc, core/debug: Don't expose absolute kernel addresses via wchan
commit b2f73922d119686323f14fbbe46587f863852328 upstream.
So the /proc/PID/stat 'wchan' field (the 30th field, which contains
the absolute kernel address of the kernel function a task is blocked in)
leaks absolute kernel addresses to unprivileged user-space:
seq_put_decimal_ull(m, ' ', wchan);
The absolute address might also leak via /proc/PID/wchan as well, if
KALLSYMS is turned off or if the symbol lookup fails for some reason:
static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task)
{
unsigned long wchan;
char symname[KSYM_NAME_LEN];
wchan = get_wchan(task);
if (lookup_symbol_name(wchan, symname) < 0) {
if (!ptrace_may_access(task, PTRACE_MODE_READ))
return 0;
seq_printf(m, "%lu", wchan);
} else {
seq_printf(m, "%s", symname);
}
return 0;
}
This isn't ideal, because for example it trivially leaks the KASLR offset
to any local attacker:
fomalhaut:~> printf "%016lx\n" $(cat /proc/$$/stat | cut -d' ' -f35)
ffffffff8123b380
Most real-life uses of wchan are symbolic:
ps -eo pid:10,tid:10,wchan:30,comm
and procps uses /proc/PID/wchan, not the absolute address in /proc/PID/stat:
triton:~/tip> strace -f ps -eo pid:10,tid:10,wchan:30,comm 2>&1 | grep wchan | tail -1
open("/proc/30833/wchan", O_RDONLY) = 6
There's one compatibility quirk here: procps relies on whether the
absolute value is non-zero - and we can provide that functionality
by outputing "0" or "1" depending on whether the task is blocked
(whether there's a wchan address).
These days there appears to be very little legitimate reason
user-space would be interested in the absolute address. The
absolute address is mostly historic: from the days when we
didn't have kallsyms and user-space procps had to do the
decoding itself via the System.map.
So this patch sets all numeric output to "0" or "1" and keeps only
symbolic output, in /proc/PID/wchan.
( The absolute sleep address can generally still be profiled via
perf, by tasks with sufficient privileges. )
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: kasan-dev <kasan-dev@googlegroups.com>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20150930135917.GA3285@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[ kamal: backport to 3.16-stable: proc_pid_wchan context ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
-rw-r--r-- | Documentation/filesystems/proc.txt | 5 | ||||
-rw-r--r-- | fs/proc/array.c | 16 | ||||
-rw-r--r-- | fs/proc/base.c | 9 |
3 files changed, 20 insertions, 10 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index ddc531a74d04..225ae3ba74b3 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -139,7 +139,8 @@ Table 1-1: Process specific entries in /proc stat Process status statm Process memory status information status Process status in human readable form - wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan + wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function + symbol the task is blocked in - or "0" if not blocked. pagemap Page table stack Report full stack trace, enable via CONFIG_STACKTRACE smaps a extension based on maps, showing the memory consumption of @@ -301,7 +302,7 @@ Table 1-4: Contents of the stat files (as of 2.6.30-rc7) blocked bitmap of blocked signals sigign bitmap of ignored signals sigcatch bitmap of caught signals - wchan address where process went to sleep + 0 (place holder, used to be the wchan address, use /proc/PID/wchan instead) 0 (place holder) 0 (place holder) exit_signal signal to send to parent thread on exit diff --git a/fs/proc/array.c b/fs/proc/array.c index 3e1290b0492e..98f368b7c857 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -371,7 +371,7 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns, static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, struct pid *pid, struct task_struct *task, int whole) { - unsigned long vsize, eip, esp, wchan = ~0UL; + unsigned long vsize, eip, esp, wchan = 0; int priority, nice; int tty_pgrp = -1, tty_nr = 0; sigset_t sigign, sigcatch; @@ -508,7 +508,19 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, seq_put_decimal_ull(m, ' ', task->blocked.sig[0] & 0x7fffffffUL); seq_put_decimal_ull(m, ' ', sigign.sig[0] & 0x7fffffffUL); seq_put_decimal_ull(m, ' ', sigcatch.sig[0] & 0x7fffffffUL); - seq_put_decimal_ull(m, ' ', wchan); + + /* + * We used to output the absolute kernel address, but that's an + * information leak - so instead we show a 0/1 flag here, to signal + * to user-space whether there's a wchan field in /proc/PID/wchan. + * + * This works with older implementations of procps as well. + */ + if (wchan) + seq_puts(m, " 1"); + else + seq_puts(m, " 0"); + seq_put_decimal_ull(m, ' ', 0); seq_put_decimal_ull(m, ' ', 0); seq_put_decimal_ll(m, ' ', task->exit_signal); diff --git a/fs/proc/base.c b/fs/proc/base.c index 71d855747fe8..2d038a7e16a1 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -236,13 +236,10 @@ static int proc_pid_wchan(struct task_struct *task, char *buffer) wchan = get_wchan(task); - if (lookup_symbol_name(wchan, symname) < 0) - if (!ptrace_may_access(task, PTRACE_MODE_READ)) - return 0; - else - return sprintf(buffer, "%lu", wchan); - else + if (wchan && ptrace_may_access(task, PTRACE_MODE_READ) && !lookup_symbol_name(wchan, symname)) return sprintf(buffer, "%s", symname); + else + return sprintf(buffer, "0"); } #endif /* CONFIG_KALLSYMS */ |