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authorJiri Slaby <jslaby@suse.cz>2017-10-23 13:41:51 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-11-10 07:42:54 -0800
commitda92e8a2d986ac1c3a8c613b4760b6dccd359bb3 (patch)
treee10e1d3524295abecdd1c72d20249730b1b9d547 /kernel
parenta2b9a0def3e99bfa064364dc6c21b5eccb06db2e (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.c12
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;
}