[PATCH bpf v1 09/10] bpf: Mark syscall helpers as sleepable

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

bpf_sys_bpf() executes the bpf(2) syscall body, which can take mutexes,
allocate with GFP_KERNEL, and wait for an RCU grace period.
bpf_sys_close() reaches close_fd() and filp_close(), which can sleep as
well.

Both helpers are limited to BPF_PROG_TYPE_SYSCALL, whose main program is
sleepable. That does not make every callback sleepable: a syscall program
can register a bpf_timer callback, and the verifier checks that callback
in a non-sleepable context while retaining the syscall helper set.

Without .might_sleep on the prototypes, such a callback can invoke
bpf_sys_bpf() from hrtimer softirq context and trigger a
scheduling-while-atomic failure. bpf_sys_close() is exposed through the
same missing context check.

Set .might_sleep on both prototypes so the existing helper-context check
rejects them from timer callbacks and other atomic regions. Calls from the
sleepable main body remain valid.

Fixes: 79a7f8bdb159 ("bpf: Introduce bpf_sys_bpf() helper and program type.")
Fixes: 3abea089246f ("bpf: Add bpf_sys_close() helper.")
Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/syscall.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6874ba1424af..c7bc9ba9b331 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -6568,6 +6568,7 @@ EXPORT_SYMBOL_NS(kern_sys_bpf, "BPF_INTERNAL");
 static const struct bpf_func_proto bpf_sys_bpf_proto = {
 	.func		= bpf_sys_bpf,
 	.gpl_only	= false,
+	.might_sleep	= true,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_ANYTHING,
 	.arg2_type	= ARG_PTR_TO_MEM | MEM_RDONLY,
@@ -6593,6 +6594,7 @@ BPF_CALL_1(bpf_sys_close, u32, fd)
 static const struct bpf_func_proto bpf_sys_close_proto = {
 	.func		= bpf_sys_close,
 	.gpl_only	= false,
+	.might_sleep	= true,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_ANYTHING,
 };
-- 
2.53.0