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authorBen Wolsieffer <ben.wolsieffer@hefring.com>2023-10-19 23:45:49 +0300
committerIngo Molnar <mingo@kernel.org>2023-10-27 12:53:42 +0300
commitc73801ae4f22b390228ebf471d55668e824198b6 (patch)
tree3ff2d2f1871b78a9f626c9457a421e3ea4343fe4
parent184fdf9fc7ae6ae7155768faa48fc609d1a24b7e (diff)
downloadlinux-c73801ae4f22b390228ebf471d55668e824198b6.tar.xz
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 <ben.wolsieffer@hefring.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Darren Hart <dvhart@infradead.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: André Almeida <andrealmeid@igalia.com> Link: https://lore.kernel.org/r/20231019204548.1236437-2-ben.wolsieffer@hefring.com
-rw-r--r--kernel/futex/core.c12
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index ade7c731972d..52695c59d041 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;
}