From e78c38f6bdd900b2ad9ac9df8eff58b745dc5b3c Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Mon, 23 Oct 2017 13:41:51 +0200 Subject: [PATCH] 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 Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Darren Hart Signed-off-by: Linus Torvalds --- kernel/futex.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 0518a0bfc746..0d638f008bb1 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; } -- GitLab