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| author | Ben Wolsieffer <ben.wolsieffer@hefring.com> | 2023-10-19 23:45:49 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2023-11-20 13:58:53 +0300 |
| commit | d7bbdc9bf41dcbeaefeb239647d9c5bd3995a1aa (patch) | |
| tree | 9a678048662af33202ed5bafa567b5697eaa81bf | |
| parent | 626ea25e6d1d416d4b85f583e2dbcd6ebc48f081 (diff) | |
| download | linux-d7bbdc9bf41dcbeaefeb239647d9c5bd3995a1aa.tar.xz | |
futex: Don't include process MM in futex key on no-MMU
[ Upstream commit c73801ae4f22b390228ebf471d55668e824198b6 ]
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
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | kernel/futex/core.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/futex/core.c b/kernel/futex/core.c index f10587d1d481..f30a93e50f65 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -248,7 +248,17 @@ int get_futex_key(u32 __user *uaddr, bool fshared, 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; } |