From: Ben Wolsieffer Date: Thu, 19 Oct 2023 20:45:49 +0000 (-0400) Subject: futex: Don't include process MM in futex key on no-MMU X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=c73801ae4f22b390228ebf471d55668e824198b6;p=linux.git futex: Don't include process MM in futex key on no-MMU On no-MMU, all futexes are treated as private because there is no need to map a virtual address to physical to match the futex across processes. This doesn't quite work though, because private futexes include the current process's mm_struct as part of their key. This makes it impossible for one process to wake up a shared futex being waited on in another process. Fix this bug by excluding the mm_struct from the key. With a single address space, the futex address is already a unique key. Fixes: 784bdf3bb694 ("futex: Assume all mappings are private on !MMU systems") Signed-off-by: Ben Wolsieffer Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Cc: Thomas Gleixner Cc: Darren Hart Cc: Davidlohr Bueso Cc: André Almeida Link: https://lore.kernel.org/r/20231019204548.1236437-2-ben.wolsieffer@hefring.com --- diff --git a/kernel/futex/core.c b/kernel/futex/core.c index ade7c731972dd..52695c59d0411 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -252,7 +252,17 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key, * but access_ok() should be faster than find_vma() */ if (!fshared) { - key->private.mm = mm; + /* + * On no-MMU, shared futexes are treated as private, therefore + * we must not include the current process in the key. Since + * there is only one address space, the address is a unique key + * on its own. + */ + if (IS_ENABLED(CONFIG_MMU)) + key->private.mm = mm; + else + key->private.mm = NULL; + key->private.address = address; return 0; }