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| author | Jiri Slaby <jslaby@suse.cz> | 2017-10-23 13:41:51 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-11-10 07:42:54 -0800 |
| commit | da92e8a2d986ac1c3a8c613b4760b6dccd359bb3 (patch) | |
| tree | e10e1d3524295abecdd1c72d20249730b1b9d547 /kernel | |
| parent | a2b9a0def3e99bfa064364dc6c21b5eccb06db2e (diff) | |
futex: futex_wake_op, do not fail on invalid op
[ Upstream commit e78c38f6bdd900b2ad9ac9df8eff58b745dc5b3c ]
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/futex.c | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index c3ea6f2a6997..053d7be08be5 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1467,8 +1467,16 @@ 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; } |