futex: futex_wake_op, do not fail on invalid op
In commit 30d6e0a4190d ("futex: Remove duplicated code and fix undefined
behaviour"), I let FUTEX_WAKE_OP to fail on invalid op. Namely when op
should be considered as shift and the shift is out of range (< 0 or > 31).
But strace's test suite does this madness:
futex(0x7fabd78bcffc, 0x5, 0xfacefeed, 0xb, 0x7fabd78bcffc, 0xa0caffee);
futex(0x7fabd78bcffc, 0x5, 0xfacefeed, 0xb, 0x7fabd78bcffc, 0xbadfaced);
futex(0x7fabd78bcffc, 0x5, 0xfacefeed, 0xb, 0x7fabd78bcffc, 0xffffffff);
When I pick the first 0xa0caffee, it decodes as:
0x80000000 & 0xa0caffee: oparg is shift
0x70000000 & 0xa0caffee: op is FUTEX_OP_OR
0x0f000000 & 0xa0caffee: cmp is FUTEX_OP_CMP_EQ
0x00fff000 & 0xa0caffee: oparg is sign-extended 0xcaf = -849
0x00000fff & 0xa0caffee: cmparg is sign-extended 0xfee = -18
That means the op tries to do this:
(futex |= (1 << (-849))) == -18
which is completely bogus. The new check of op in the code is:
if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
if (oparg < 0 || oparg > 31)
return -EINVAL;
oparg = 1 << oparg;
}
which results obviously in the "Invalid argument" errno:
FAIL: futex
===========
futex(0x7fabd78bcffc, 0x5, 0xfacefeed, 0xb, 0x7fabd78bcffc, 0xa0caffee) = -1: Invalid argument
futex.test: failed test: ../futex failed with code 1
So let us soften the failure to print only a (ratelimited) message, crop
the value and continue as if it were right. When userspace keeps up, we
can switch this to return -EINVAL again.
[v2] Do not return 0 immediatelly, proceed with the cropped value.
Fixes: 30d6e0a4190d ("futex: Remove duplicated code and fix undefined behaviour")
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhart@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/futex.c b/kernel/futex.c
index 0518a0b..0d638f0 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1570,8 +1570,16 @@ static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
int oldval, ret;
if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
- if (oparg < 0 || oparg > 31)
- return -EINVAL;
+ if (oparg < 0 || oparg > 31) {
+ char comm[sizeof(current->comm)];
+ /*
+ * kill this print and return -EINVAL when userspace
+ * is sane again
+ */
+ pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
+ get_task_comm(comm, current), oparg);
+ oparg &= 31;
+ }
oparg = 1 << oparg;
}
